On 11-MAY-1996 03:28:33.7 vanderzande.frank said to JKAHRS
> Trinidad and Tobago - North America or South America ??????
The ARRL DXCC Countries List has 9Y in SA ITU 11 CQ9
>From email@example.com (Brian Short) Sun May 12 15:49:02 1996
From: firstname.lastname@example.org (Brian Short) (Brian Short)
Subject: Mother of All Amp Summaries
OK Jim et. al. here is the whole enchilada! 73 de Brian
(email@example.com aka DORK)
From: Jim Reisert AD1C[SMTP:AD1C@tiac.net]
Sent: Sunday, May 12, 1996 3:52 AM
To: Brian Short
Subject: Re: Mother of All Amp Summaries
On Sat, 11 May 1996 15:03:28 +-100, Brian Short wrote:
>Read the attached file. I'll summarize the rough neighborhood stuff later.
Whatever was in that ZIP file, it was corrupt when it arrived here, even
Jim Reisert <AD1C@tiac.net> http://www.tiac.net/users/ad1c/
From: Brian K. Short[SMTP:firstname.lastname@example.org]
Sent: Wednesday, April 10, 1996 16:40
To: 'email@example.com'; 'wf1b-rtty'
Subject: Choosing an RTTY Amplifier (VERY LONG)
Perhaps a talented, technically oriented individual can "summarize"
this mass of information. It is logically inconsistent, somewhat
esoteric, and self-contradictory! I included it all, so YOU judge
Many suggestions recommending the "Yellow Sheets" for used amps were
received. A good URL is http://www.westes.com/Ads/ and for those who
enjoy USENET, try news:rec.radio.swap. I found little of interest
at these locations, but your mileage may vary and I don't want to buy
10-20 year old equipment sight unseen, untested (by me).
Appologies to one individual for nearly consumating a deal on an older
Alpha amp which is no doubt a good amp for someone living in MN who can
inspect it. Comments on internet and by telephone recommended AGAINST
buying an amp without seeing it and testing it.
Next, my decision. I decided to purchase an Ameritron AL-1200 with
the 3CX1200 tube for $1849 + $12.00 s/h & insurance = $1866 shipped
today (AES has about 10 in stock and charges flat $12 shipping based
on PRICE not WEIGHT. I dealt with WB8WEN (Bob) in Ohio who was very
helpful (ask for him). My amp will ship from Las Vegas (to AZ), but
their stock is scattered. Waiting for a production run can require
patience. That was my decision, here's why:
1) positive comments below regarding durability and value
2) very good value (bang for buck) with 1 yr "NO MATTER WHAT WARRANTY"
3) I already have an automatic tune (solid state) QSK amp when needed
these features would be redundant
4) availability: Alpha quoting 3 mos on 91B with price increase likely
and delays will only become greater post-Dayton, Command quoting 3
or 4 weeks (not bad) again with price increases likely and Dayton
5) this a NEW peice of gear with a NEW tube and Hypersil transformer
6) I don't demand 1.5kw+ continuous, I can get by running with a bit
less drive and it won't show on anyone's S-meter (I'm no BIG GUN)
7) shipping expenses: this was a GREAT deal on shipping
If/when a mint used amp that I can inspect and test comes my way, I
may purchase it too, but I feel much less pressure at this time.
Comments, tell me I'm crazy etc, all welcome. Many asked for the
amplifier information, so here it is. Some asked for the "scraps
off my plate" and there are many depending on your city, but NO
recommendations from me, see the HTTP URL.
Below are comments received about various HF linear amplifiers:
(Included are HENRY, ALPHA (emphasizing the 91B), AMERITRON (AL-1200
and AL-1500 models only), TEN TEC, COMMAND (HF-2500), QRO, HEATHKIT
(SB-220), and HOMEBREW (emphasizing the 4-1000) in this random order.
I have been using a Henry 3k Premier here for about 6 years now with no
trouble at all. I run 1500 watts key down in just about every RTTY contest
there is. I have run multi op efforts with close to 48 hours of operation
without a problem
The 3k premier uses one 1200A7 tube and is one rugged amplifier, and I would
highly recommend it for anyone wanting key down power at the full legal limit.
Mine is the consule model that sits on the floor and weighs 210 pounds, I
paid 2900 for it in 1990, so not sure what they go for now.
Incidently this amp can take lots of abuse. I've run it into open loads ran
it on 40 meters on the 20 meter beam and a variety of other stupid mistakes
that often happen alot late at night (dont tell anyone else this!) and it
jsut keeps pumping out the power without a hitch.
Another thing is if you order a Henry be sure to ask for the export model
which includes a heavy duty transformer, the domestic models cannot produce
the same power output as the export models. Mine has 4400 Plate voltage
while the domestic one only has 3900 Volts on the plate.
More power to Ya!
Ok Brian, it will cost you a little more but NOTHING is better than
an Alpha-87A.. 45 wts drive, gives you, 1500 wts out....
It does cost a little more to go first class.. But it is the BEST,
Hi Brian: Your scores are consistently too high. You should run QRP
in contests so my wires have a chance!!
On a more serious note...I run the Alpha 87A with auxiliary fan,
wired on all the time. I run full 1500 watts and run RTTY contests
regularly. Antennas are all 1.5:1 or less and everything runs fine.
Also keeps the shack warm in the cold MN winters. I've heard of some
who put a switch on the second fan and only run it on RTTY as it is
REAL noisy, but I just put on the earphones when on SSB and press on.
I've tore up a lot of KW amplifiers running the RTTY
contests over the years. Two amplifiers have stood up
to the test... the Alpha 87A and the Ameritron AL-1500.
I just purchased a second Alpha 87A so I am selling my
Ameritron. It uses the 8877/3CX1500A7 tube and has no
trouble generating 1500 watts of RF. You need less than
100 watts of RF to drive the amplifier to full output.
During the RTTY contests I run my amplifiers between
1000 and 1200 watts output. No one can tell the difference
in my signal and it allows my transceiver to run cooler,
My Ameritron AL-1500 had the QSK kit but I had so much
trouble with it, I rewired the amplifier back to the stock
factory condition. I'll toss the QSK board/documentation
in with the amplifier package for anyone that has a lot of
extra time on their hands and wants to replace RF "fuses"
whenever they mistune the amplifier for more than a ms.
That was the only problem I experienced with the unit. I
am the second owner, low hours, looks and runs like new, has
sat under the bench as a spare, only driven when the Alpha
was in the shop being serviced, your mileage may vary, etc...
Call Ray Heaton at ETO in Co. (719)260-1191. The ETO 91B is rated at 1500+
any band(160-10), any mode - no time limit!! 2495US$. Mine ships next
monday. About 8 week
IMHO, the 91b is junk. It blew up on me after 30 minutes or so, running
1300 watts at YK0A. It also failed last year at Conway Reef and
Scarborough. I suggest--again--if you are serious about running 1.5kw on
rtty in contest conditions that you get something like the Henry 5k or
even the 8K . They are cheap for what they do and will run cool at legal
power just like smaller amps run well at 500 watts but not at 1500. No
amateur amp that I know will run 1.5 KW on rtty in contest conditions for
a full weekend, and I think I have tried all of them, including 3-hole
3cx800 models (ARD). The latest failure I experienced was the power
supply in my IC-4KL when I was contesting at about 1200 watts.
Brian - I just placed my order for an ETO 91B about 2 weeks ago.
According to ETO's Ray Heaton it should do fine on RTTY 1.5kw
output providing you add the optional $40. external cooling
fan. I had already intended to add it anyway.
There were some comments from folks I spoke with that had
some reservations about the old-style HV diodes used in the
plate power supply. But ETO assured me that if the diodes
(which are from Eastern Europe) could not be obtained for
replacement that the HV diode blocks as used in the 89/87A
could be used.
The plate transformer is also manufacured in Eastern Europe
and the quality of the "hysil" type steel used in the core
was unsure. But I found out the steel is from the U.K. and
is imported into whereever in E. Europe the xfmr is made.
Also, Peter Dahl Co. (El Paso, TX) can supply a replacement
transformer if they can obtain the mechanical and electrical
specs in case the factory transformer ever becomes unavailable.
As for the Russion (Svetlana) 4CX800 tubes, the ARRL Lab
has told me that the Russian tubes are of good quality,
certainly much better than the Chinese tubes that are
being imported. RF Parts is a Svetlana distributor
and has told me that they have experienced no more
problems or returns with the Russian tubes than
The only problem with the 91B is delivery. I was told
mine would be available "last week of June/first week of
July". They are becoming popular.
I have had my 91B for about 4 months.....Pro's first.
1. Easy to install and set up.
2. Easy to tune and good self protection.
3. Signal sounds clean.
4. Price was right.
1. One tube arrived dented, and I was told to live with it.
2. Incomplete documentation....no schematic supplied.
3. average and peak output metering do not match.
4. Attitude of ETO's service person needs a dramatic improvement.
5. Cheap price means cheap components (switches and the like)
Overall....I like it. But for hard core contesting...I'll get an 87A
I have had one about 6 weeks now. I find it easy to operate and it
appears to operate as expected. It has plenty of reserve capacity and is
well designed from the standpoint of interlocks and protective circuity.
You don't find that in most of the other models. Product review in NCJ
last Summer sometime.
The exciter (an 850 in my case) is happy because it always sees a
resistive load (you are driving across a 50 ohm resistor). Tuneup is fast
once you establish the tuning and loading settings for your antennas.
On SSB, it is very easy to exceed the legal limit. I had to back way down
to almost nothing on mike gain. On CW, it requires maybe 65 watts out for
a full 1.5KW out.
Lots of blinking LEDs while operating, but once you get used to all that,
no problem. You can run the thing at 1.5 KW out all day long if you want.
The only thing that happens is the shack gets warm because of all the
extra heat generated. At legal limits, you are never going to hurt this
Hi Brian,We run a pair of these Alpha 91b's.We bought them back in sept
of 95.These amps are have proven to be a excellent asset to our contest
efforts.We ran them full bore in a few contests with not a glitch.The
amps does more power (if it matters) than the 87 + 89's,The tuning is
very smooth and the amp is the quietest thing I've ever seen.We'll be
adding 2 more of these amps as well finish constructing a m/m station.
I beleive for what they ask for the amp,It absolutly delievers the most
bang for the dollar.GL Regards
It will do it but there is provisions for an extra blower and it
is recommended for RTTY contesting. About $60 extra.
I'm using the Alpha 87A at 1500W ouput with no problem but I
don't know if you want to spend that kind of money for rtty contesting.
I use it for all modes with the ETO digital antenna switch for instant band
and antenna switching but you really don't need that kind of band
switching speed for rtty contests as the pace is not that fast. :-)
I think you can run an AL-1200 at about 1 kw output. That should
do the job. I had an AL-1200 and that is a good amp. Got rid of it when
I bought the 87A but stll have an Alpha 374A for the 2nd station. I ran
that at about 700w output. I like that amp because it is a no-tune amp.
Make sure you have a good powerline. We used a 3 kW generator that should be
ok to drive it
but to about 1 KW out but the voltage in the cables fluctuated a bit too
much for the amp
forcing the amp into STBY mode all the time on Conway. This happened even
down at 500W. We masured the voltage at the Generator and there it was OK
all the time.
Mine works great electrically. Mechanically the fan is not up to ETO
standards. I have had it back twice. It was SUPPOSED to be returned to me
2 day UPS with a NEW fan by today. Its WPX Friday night and I dont have it.
Ray Heaton is going to get an ear full as he promised it to me earlier this
week. What happened to the fan? Bearings went out. It sounded like a
screaming banshee. The firt time back was for a seized fan...they could not
duplicate the problem.
Gives new meaning to ...a screaming amp!
For the key down stuff...RTTY, you need the optional transformer fan.
Cost approx $40.
When the beast is a workin'...it smokes. Sure doesnt do me much good on
ETO's bench tho!
I hope someone else besides Ray reads this at ETO because I'm p****d !
I've had mine, a beta unit, since last year's ARRL DX CW contest. It has
been back once. One of the Svetlana tubes went bad. The turn around was
less than ten days. Since then, I had a problem with the vacuum relay for
QSK. It got stuck in the transmit position. I called Ray and he asked if I
wanted to send it back. I told him I thought I could replace the defective
part. Ray said he'd put a new relay in the mail. That was six weeks ago,
and I'm still waiting for the replacement relay. I tapped the ill-behaved
unit with a screwdriver and have been back in business ever since.
As far as power goes, 1500 watts out easy. With the exception of the
problems noted above, the amp has performed flawlessly.
It has been back to the shop twice for repairs. First was the power
transformer and now the fan. I don't think he has had it on rtty yet,
but two times back for a new amp is not a good sign. If you want to
talk to him direct, his e-mail is "firstname.lastname@example.org". Good luck and
hope to cu in the EA-RTTY with my new TS-850.
I believe I recently sent you e-mail regarding a 4-1000 amp question and
may have mentioned that I have on order an ETO Alpha 91B amp.
The 91B is going to replace my current amp, a Henry 2K-4. This is
an amp that covers 80-10M and runs a pair of 3-500Z's. I have run
this amp at 1kw out on RTTY in several RTTY contests and numerous
SSB contests over the years without a problem. It does run quite
warm after several hours of calling "CQ CONTEST" on RTTY but has
never failed. I usually run it around 600-1kw output. It just
plays and plays. This amp is a floor console model and weighs
135 lbs. - no light-weight. The power-transformer was replaced
several years ago with a Peter Dahl Co. (El Paso, TX) hipersil
transformer. The power-supply choke is also a P. Dahl Co.
replacement choke. I have two pairs of Eimac 3-500Z tubes, both
pairs used but good and both pairs put out 1kw.
Price is $1,050. plus crating and shipping expense. I have been
told shipping crates are available from Henry Radio.
Hi Brian - I am using an ALpha 78, and am pleased with it. For short
stints will run full power (1500). If contesting and CQing, usually run
1000 or so.
I found mine on our Packet Cluster. Lot of gear advertised there. Another
source is the Yellow Sheets, so I hear, but have never used it.
I waited about 2 years for the right amp and price to come along, so
The Alpha 374 is a 3 tuber, 374A is 2 tuber. I think that price
is high. I don't think they've made the 374 or 374A for quite a few years
so mint or not, it is old. I'm not familiar with the going used prices
but that sure sounds high to me. I would buy a NEW AL-1200 (for $1700)
before I would spend $1700 for a used 374. You will get 1500w out of a
374 but I don't think I would run it on rtty at 1500w output (that would
be pushing it). 8874's are expensive tubes. You might ask someone who
has an AL-1200 what they run it at on rtty. I think I was afraid to run
it over a kw output but that doesn't mean you can't do it. I would be
curious to know what others safely run them at.
Brian, have you looked in the Amateur Radio Trader or the "Yellow
Sheets"? These two would probably be your best bet for used
amplifiers. One of your better "bang for the buck" amps you might find
is the Ameritron AL-1200. 1 kw with 50 watts drive, or 1.5 kw with 90
or so watts. And I have seen them used in the above mentioned papers
for around $1600-1800. Uses a 3CX1200A7. If you need info or addresses
for the above, drop me an E-mail message and I'll be happy to dig them
out for you. You can find the address's in the back of CQ or QST I
believe. 73 and happy RTTY'ing!
I have an AL1200 that I purchased in 1989. It replaced two homebrew amps
which used 2x3-500Zs and a single 4CX1500B.
Generally, I find the 3CX1200A7 quite rugged. I run it at 1500W near
continuously during DX contests. On RTTY I also run 1500W, but have never
used it during a contest. It does get very hot on RTTY, but with the fan
on the highest (read loudest) of the four settings, it stays at a steady
1500W. This is unlike my 4CX1500, which tended to drop off the longer I
kept transmitting. But that was an old commercial pull that just kept
Overall, I find the single 3CX1200 has been many times more rugged than the
3-500s which only lasted me one to two years before deteriorating to less
than 1500W. I am still using my first tube after 7 years, although, I now
have a spare just in case of a failure. Hi Hi.
The AL1200 can be modified to use a pair of 3CX1200s by adding a filament
transformer, tube socket, chimney, and a few miscellaneous parts. When I
was interested in trying RTTY contesting, I talked with the guys at
Ameritron about it (before the MFJ merger), and they indicated that it
could be easily done. They said it would take a bit more drive to get
1500W output since it would not be quite as efficient. My AL-1200 takes
right at 90W drive for 1500W output.
That is about all I can think of to say today.
Bottom line on AL1200:
Had one for a year - solid LEGAL output amp (will do about 1700 watts if you
drive it with 125 watts, but that's about it) . I agree with you on power - I
don't want to own a bigger amp. Even if you don't run it illegally, people
will always wonder about it, and there is that temptation to push it in the
heat of battle. Reputation is all you have in the contesting world - why ruin
it by running a big amp?
The fan is a bit noisy - operates WARC bands also (12 and 17m). I use it on
RTTY at about 600-800 watts out with no problems. It may do more, but I
didn't want to push it or my 100w (FT990) exciter under 100% duty cycle
keydown for a measly 2.5 dB.
IMHO - It's THE amp to buy - the best amp for the money out there.
I'd be glad to answer any other questions you may have on the AL1200.
I have had an Ameritron AL-1500 for several years now and had a lot of
problems at first: kept popping the clamp diode between ground and B- and
once it arced over in the PS and took out an IC as well as the diode. In
looking at the schematic I saw that there was no cathode return when the
T/R switch was in the RX position - I placed a resistor across the relay
contacts and haven't had a problem since then. I think it was 10K or 15K,
I'm not sure, and it was a 10W ww. Since then it has been trouble-free; we
have used it heavily during M/M operations and it is even my day-to-day amp.
I have added QSK with vacuum relay and electronic bias switch and now it is
a pretty good amp. It run fines at 1500w out, but I wouldn't push it any
harder; I don't think the PS or the cooling is designed for more than 1500w.
AL7CQ had an AL-1500 and he even popped an 8877 or two along with those
clamp diodes. I suspect the same problem as mine. OTOH, they have an
AL-1500 at the Kwajalein Radio Club (V7X, etc.) and I don't think they have
ever had any problems. These amps tune real sweet, set the load in the
middle and the tune to the desired band and you're close enough to start
tweaking. I also own a Titan and I never know where to start out on that.
As for the Alphas, I own a 76CA and have a lot of time on 78's and 77's. A
77 is probably a better amp (huskier power transformer, better T/R
switching, for example) than the AL-1500, but it also costs a lot more.
Still, AL-1500's can do the job at the 1500 watt level.
been using an AL-1200 for year+ on rtty and other digital modes. no
problems. had to get the QSK switch tho. it just beat the mech. T/R to
death. not fast enough either. amps r clean, uses a 3CX-1200.
Here is my input / recommendations concerning the Ameritron AL-1200 and
I used a brand new AL-1200 with 3CX1200A7 tube during the CQWW SSB contest at
the end of last October and for about 2 months afterwards (a friend of mine
bought it for the contest). I ran the amp at 1500 watts out on all bands
for the entire contest and it was solid as a rock! Tunes very nice on all
bands - the vernier loading contols are nice. The AL-1200 uses the Eimac
3CX1200A7 ceramic / metal power triode out of the Varian power grid and x-ray
The tube is very rugged and has a Grid disdipation of 50 Watts! This tube is
just about an "instant on tube". One would really have to try hard to kill
this tube. A friend of mine has a Henry amp with a 5 volt filament verion of
this tube. Henry runs around 4kv on the plate - Ameritron runs 3300 key
down--- I also used the AL-1200 during the ARRL 160M CW contest in December.
The antenna tuner arced couple of times - never bothered the amp at all!!
I placed an order for the AL-1200 for me in November. In January I changed
my mind and decided to buy the AL-1500 - this is why ---
1. The 3CX1200A7 takes a full 100 watts drive to get 1500 watts out. That
means running my Omni-6 at full power out all of the time --- The AL-1500
3CX1500A7 takes about 50W max to get 1500 Watts out on all bands! My Omni-6
loafs along at 30 - 50 watts output!!
2. The Filament on the 3CX1200A7 draws 21.3A at 7.5V = 160 Watts -
The Filament on the 3CX1500A7 draws 10.5A at 5.0V = 52.5 Watts --
(The AL-1200 is a real heat generator)
3. The 3CX1500A7 is a ceramic and metal, power triode out of the Varian Eimac
Power Grid Tube Division. The maximum grid dissipation is 20 Watts -- So you
need to watch this a bit closer. The AL-1500 does have a grid current
sensor/shutdown circuit that protects the tube. The tube is not instant on!
It takes a full 3 minutes for the filaments to reach the proper temp and then
the power relays pull in via the 3 min timer.
If I was using a rig with over 100 Watts out I may have stuck with the
AL-1200. It would not be good to hit the AL-1500 3CX1500A7 with 150 watts
drive!!, although the grid current protection circuit would take the amp back
to "stand-by". An inexperenced operator may be better off with the AL-1200
because it would be difficult to kill that amp.
Another thing of interest is the 3rd and 5th order Intermodulation Distortion
Products ratings of the tubes--
3CX1200A7 3rd is -30 db at 3500 EP, 5th is -43 at 3500 EP
3CX1500A7 3rd is -38 db at 3500 EP, 5th is -41 at 3500 EP
Other observations common to both amps:
1. The blower is very very noisey!! A vacuum cleaner is louder though!!
2. The antenna relay is loud - but built solid
3. All coils are air wound - no torids in output -- Better?? I think so ---
You can change the blower motor speed by moving a tap (soldering
4. Modification to go above 15M is very easy!! (could do with eyes closed)
I thought about buying the amp with the internal QSK installed --- I decided
not to do so because if anything happended to the QSK pin diodes it would
mean returning the amp to the factory -- that would be a real pain!! The
factory "rep" actually recommended that I buy the external QSK box -- as the
cost was the same and it could be used on any amp I have! I have had my
AL-1500 for over a month and really like it -- Very rarely does the grid
current ever exceed 25Ma and I only triped the grid current once - Ran amp
into an open!! Not the best thing to do --- but the grid protection does work
fine!!. The amp runs fairly cool at 1500 out -- The case next to the tube
warmed up a bit after a 1 hour SSB QSO where I did alot of talking. I ran it
during the 160M CQWW CW contest this January - It remained cooooool ---- I
have not received the QSK box yet -- It has been on back order for over a
month -- (Got tired of waiting and cancelled order for QSK box)
Last May I had a deposit on an Alpha 89 - 3CX800A7 (2) Amplifier - for
considerable more money -- I cancelled the order when household expenses
became primary importance - hi hi --- I had the unit on order for 2 months
prior to cancelling the order --- thats one of the problems with having to
wait so long - one can change his or her mind!!! Oh well --- The Alpha 87
and 89 are rock solid amps and they are QUIET!! Not like being next to a jet
plane taking off!! But the cost is $1000 more!! ETO had a Alpha 89 running
at 1500 Watts out for ever at Dayton last May!! Getting back to the
Ameritron - I like meters!!! Don't know if I would have liked the Alpha
"Light Show" -
Here's a quick and dirty way to quiet an AL-1200, all based
on the principle that "sound doesn't like to turn corners."
Take one end off a shoe box bottom and tape it over the
intake grill so that air is sucked into the box from the
back. Take another shoe box bottom and tape it over the
"air out" grill on top of the amplifier, again pointing to
the rear, forcing air out to go away from you.
Go to an office supply store and buy the largest typewriter
pad you can find. Go quickly. They may no longer know what
a typewriter is. This pad goes under the amplifier to
Now you've got a dampened box and air movement away from
your ears. Make sure that the air is aimed at a non-
reflective surface. Cloth or a piece of rug to absorb
In my case, I found the old typewriter pad, so the cost of
these external mods was ZERO. They make a BIG difference.
Make those sounds of blower noise turn corners, without
creating too much eddying of air currents.
I am running the Ten-Tec Titan on RTTY with full 1 kw output with no
problems. This is an early version I have, serial number 526. No problems
to date. You can find these amps used for about $2,000 to $2,500.
Brian, I am not aware of any amp on the market that will handle 1500
watts out put on rtty for a weekend. I am using a Ten Tec Titan and
I cut back to 750 watts for contest. It is fine to run 1500 out when
chasing dx as this does not take long to make the qso and you are
spending much more time listening to the dx station working others.
Alpha claims theirs (87 series) will run key down for the week end
but I do not believe it. The problem is with cooling. My Titan
would be fine if I were to up grade the cooling fan to something that
sounded like a jet coming in to land. Hi
a friend of mine says its great but doesn't recommend with Ten Tec HF rigs.
It ramps up so quick with the Ten Tec it creates a big time spike. He
checked with Ten Tec and they said theres no fix.
As a member of Team Antigua, V26B, we used Command Tech Amps down Island for
the entire CQWW SSB Contest 1995 without any troubles whatsoever!
Sam can answer any questions you may have about the Amps we used.
But I was very happy with the way the ones we used operated. Very easy to
and very easy to assemble and disassemble!
We had them shipped down special for the weekend, so we wouldn't have to
Like I said Please drop a note to Sam, he would be glad to answer any
question you may have. I'm just a tower monkee and 40m Op for the crew!
A friend of mine had and HF-2500 amp and liked it but the one
thing he did not like about it is the tuning is very sensitive. He did
you don't have to qsy much and you have to retune the amp.
I liked mine, very solid amp. but the fan noise drove me out of the shack.
You can call the factory direct, they hear of folks selling amps, and put an
ad out on
Hi Brian....other than being a little noisy....(the Fan) it is a good
AMP......have Alpha 87a on regular station.....and HF-2500 on the 2nd
station.....during contests we use the HF-2500 on the Run Station and
the 87a on the Mult Station.....works well....
I own a HF2500, and I think it is a really nice amp. It tunes pretty
cleanly, has power to spare and puts out a clean signal. Only bitch most
people have is that you need an outboard power meeter to tune it as it
doesn't have one.
Mine produces a strange smell on 40 meters when I use it in RTTY contests,
but I think RTTY is the biggest test for any amp.
We used it at ON4UN's in the CQWW RTTY test last fall for the mult station.
It really can easily handle 1500 watts out RTTY all weekend. John was
amazed. He took it to his bench and was able to put out 200 watts with 100
Its pretty small, and relatively light. For the money its a fie amp!
I've been using a Command Tech 2500 for over a year. Having had a 35 year
background with amps ranging from 4-400's to PL-172 I am very impressed with
this amp. The support is excellent and unlike many commercial amps the parts
are heavy duty. Pat Stein who owns and builds them is great to work with
before and especially after purchase.
I'll sum it up in two words "BUY IT".
use one of these @ our local M/M operation.
Pro: easy tune and low amount of drive for full power out (~50w). Also,
fairly quite running... been very reliable
Con: easy to overdrive (see above)
I have known him for 10 years, when he started out with QRO 2 meter amps...
He makes good equipment and he is a "straight up dude"... Give him a call and
chat.. Maybe he has a trade in?...
Thanks for all the good information on the the amplifiers that I posted
yesterday. I would like to know if anyone out there is using
an HF2000 fom QRO Technologies or a Command Technologies Amp. I
talked with Ray Connin, who owns the QRO business, and he says that
the amp business is a sideline and he has three other business going
in his location other than ham radio. He assured me that his primary source
of funds did not come from his QRO business. He says he wants to be around
IN the below $2000 range, there are not a lot of choices for amps. I have
counted the Ameritron line, Ten Tec, and QRO. They are all 3-500z amps, but
some have different features than others. I am
just curious how all the guys on the net feel about these amps.
I like to contest in CW contest, but enjoy SSB for the rate! Lets discuss
the issue here. Just interested in the discussion. Remember, below 2000
I saw your questions in the net mail and would like to pass on some of
my limited experience. I am retired mechanical engineer - 66 yrs. I have only
been an amateur since 1991 and have been almost exclusively on RTTY or Pactor
modes since that time. When I first started, the bands were very nice to work
and an amplifier wasn't really needed. As the propagation, fell it became
more desireable and now seems like it is almost required for serious DX.
For what it is worth:
1. For watts out/dollar the SB-220 is the bargain - providing you find a
"good" one. You can find excellent ones for 400 to 600 dollars. (New Eimacs
cost about $150.00 ea) - Fantastic value.
2. Take the covers off for an eyeball. Check for modifications and
workmanship. These Heath amps have been around a while and some have been
3. Check 3-550-Z's condition for clear glass all around - no "smoke" on
the inside.Take tubes out and tap lightly to check for anthing loose. I would
recommend Eimac brand over any other based on the experience of myself and my
friends with Chinese manufactured tubes. I would insist on a reduction in
price for Chinese tubes (unless price is really low) or offer to buy without
4. Insist on a live demo and check performance on all the band settings
- 10, 15, 20, 40, and 80. Check power out vs. power in for all bands. SWR
between the tranceiver and amplifier is pretty important for the newer
tranceivers because they will cut down on the output power if the SWR is too
high. A good check can be made looking at the Rig power level out with and
without the amplifier in line. If it goes way down with amp in line, you can
be sure the amplifier input circuit SWR is too high. The input SWR can be
adjusted, but it is difficult if you do it yourself or expensive if someone
else does! If not too bad, you can use an antenna tuner between them to fine
tune. I use a MFJ-941e for this purpose when operating (typical engineer) and
it works good. If using a tuner for a very high SWR, it may mismatch your
incoming signal when the antenna relay opens and you are "direct".
5. Check the filament operating voltage if you are interested in 3-500-Z
tube life. The Eimac recommendations are 4.75 to 5.25 volts. Tube life can be
doubled for every 3% reduction in filament voltage without affecting PEP
power. Heath recommends 4.85 volts for the SB-220.
6. The life of the tubes will also be a function of the power level you
operate at. The higher the output, lower the life of the tubes. Makes sense
eh? Most of the RTTY guys I have talked with say if you keep it under 500
watts the 3-500-Z tubes will last longer than you will !
7. For parts, modifications, and good information contact Allen b.
Harbach - WA4DRU 2318 S. Country Club Rd., Melbourn, FL., 32901. Tel. (407)
723 - 7145
or Richard L. Measures - AG6K, 6455 La Cumbre Road, Somis, CA, 93066
tel. (805) 386 - 3734
or RTTY buddy John P. Ardelan - KF9SF, 928 Millview Drive, Batavia, IL
60510, internet -email@example.com
For serious DXing RTTY, I would also recommend putting money in the best
antenna you can afford and/or use. It can be easier sometimes to get the
extra dB's out and extra sensitivity in with a good antenna! Takes two to
tango and you have to be able to process the DX incomming as well as sending
to him. Also, recommend use of the new DSP filters for working Pileups. I am
using the DSP-59+ and it is great. I have heard equally good words about
others too. Lastly, the use of an oscilloscope for tuning is a virtual
necessity. It is much like zero beat matching a CW tone to get on frequency.
I have found the bar graph indicators to be useless for weak signals. In
digital signal processing, being on frequency is essential for working weak
The technique of adding a parasitic suppressor in the cathode/filament
lead (in cathode driven amps) can help stabilize the amplifier if the
source of the oscillation is a true output to input oscillation
(and at VHF, of course). The advantage of the input side suppressor
is that it is on the driver (100W) side of the loop rather than on the output
(1500W) side of the loop.
>The main problems are parasitic oscillation/arcing when I tune up, unless I
>remember to start with the loading cap half-meshed. It is most pronounced
>on 80 and 15 meters...I was shocked the first time it 'spit' at me on 80
Everyone now tends to connect arcing with parasitics. Although under rare
conditions that can occur, it's a very rare case. The reason you still have
this problem after installing the parasitic mod is the problem is almost
NEVER caused by parasitics.
When an amplifier operating in class AB through C is lightly loaded, the peak
anode and tank voltage can be * several times * the anode supply voltage.
This is caused by the loaded Q of the tank circuit increasing, and the tube
being driven into and out of saturation, by high drive power and light anode
loading. The effect is actually caused by the tube "ringing" the tank at the
operating frequency, not at VHF.
Let's look at it from the standpoint of an unwanted VHF signal. If the cause
was a "VHF parasitic", the tank capacitor would present a VERY low impedance
path. If the tank capacitor was adjusted to have 300 ohms of reactance at 14
MHz, it would have ~40 ohms of reactance at mid-VHF. You can calculate the
VHF current needed to drive the capacitor to ~4000 volts at that value of
reactance. It's getting close to a short circuit for VHF (after all, that's
why the amplifier tank has VHF harmonic supression).
You'll find the tubes totally incapable of supplying enough current into that
load impedance to cause an 4000 volt arc! In rare cases I've seen arcs from
HF, or near HF oscillations. But I've *never* seen tank arcing from VHF
oscillations in an HF amp.
Here's another thing to consider. When a circuit oscillates, it's from the
overall circuit loss being less than the overall gain, and correct phase
shift. Circuits just don't "wildly oscillate" for a split second and then
quit. They either make good strong oscillators, or they don't
If circuits are at the edge of oscillating, they won't build up into an
uncontrolled high power oscillation.
HF amps arc when mistuned because it's almost impossible, and certainly not
economical, to size tank components to handle extremely high voltages caused
by underloading the tank.
>I had sort-of gotten used to the 15m instability. It will also randomly
>I first key-down -- is the circuit not loaded heavily enough??
Absolutely. The loading is too light. Not only that, MANY exciters put out a
sharp rising edge transcient before the ALC reduces the drive. I've measured
Kenwoods that slap 150 or 200 watts into a PA for several RF cycles at the
moment of transmission. Imagine the peak voltages generated at the output
when this happens. Keep in mind the SB-220 was designed to be "tuned up" in
the CW position, and operated at 600 watts output on CW (PEP) and 1200 watts
on SSB (PEP). They weren't designed to be tuned in the SSB position.
>OK, so if I slap the grids directly to ground, what kind of parasitic choke
>you recommend? I had previously used a 3 turn copper strip (abt. 1/4 inch
>wide) with a pair of 100 ohm resistors (before I installed Rich Measure's
>that includes the nichrome wire/resistors/coils in the anode).
The stock one is fine, actually it is a bit of "overkill" when the grids are
grounded. Just be sure the resistors are true carbon comps, and not
constructed with a spiral carbon or metal film inside. The reason you have
arcing, and still have it after all the mods, is the problem wasn't
parasitics in the first place. Tuning the amp incorrectly, especially tuning
it in the SSB position, and having an exciter that pulses the amp with high
drive levels, is what really causes tank arcing.
A secondary cause is relay sequencing, if the relay's output closes late
(after the input closes), the amp will operate at full drive with NO load for
I just got done homebrewing a 4cx1500 amp. Tetrodes are the way to
1. a 1500w out amp only takes 30 watts of drive, therfor the driving
rig can loaf.
2. Using what they call a passive grid system, where the grid has a
swamping resistor to RF ground and the bias supply, the following
A. The amp is exceptionally stable without neutralization
B. there is no need to bandswitch an input tuned circuit.
C. the driving rig sees a 50 ohm load throughout the full
360 degrees of the sine wave.
3. 4CX1000 and 4CX1500 tubes will last 30 years, as opposed to
the "consumable" zero bias triodes.
On the downside, it is necessary to provide some extra protection
circuitry - See QST Mark Mandelkern, KN5S, Protecting Power Tetrodes
On any amp- especially the expensive modern so-called best available
amps: Make damn sure they incorporate the parasitic suppression
ttechniques described by AG6K in QST - he also has a WWW page with
tons of info on this subject. Believe me, just because an amp is
expensive, new, and rated at full output key down, that does not mean
it will not self destruct from parasitics. If you buy an amp that does
not have the AG6K style suppressors, I urge you to put AG6K suppressors
in it before you power it up. Five bucks worth of suppressors are cheap
compared to $500 or more for a set of tubes.
Hope this info helps. Please let me know what you end up with.
The real question is where's the beef, the tube will do everything you
want it to do and more. If the rf deck and power supply you have to be
concerned with. People have run the tube between 6000 & 7200 volts
with up to an amp.
If you run it at low voltage say 4000v you will need a ton of drive
to get the tube moving, 100 watts just won't do it.
Also used tubes are common, and expect to pay around $150. It is said
a kw from a 4-1000 is louder than kw from any other tube. It appears
all dB's are not created equal!
I think you will find that the 4-1000 will require quite a bit
of drive power from your transceiver vs. the 3cx800/4cx800 class
of amps. Maybe 100+ watts. for 1-1.5kw output. Ask the owner
how much drive it takes. No sense having an amp with a big tube
if you have to run your transceiver wide-open (this means in RTTY
service it will get really hot).
It depends on how hard you want to push the tube. Thoriated tungsen filament
tubes can take a fair amount of abuse, and in amateur service you'll likely
never notice the shortening of life unless the temperature of a critical
areas (like seals) go beyond a certain limit. A 4-1000A could provide 2000
watts or more of CW or SSB PEP output without damage even during contest
I've know people to run a single tube at 3kW+ PEP out on SSB.
The biggest problem is drive power and stability. The 4-1000 is "hard to
drive". In grounded grid, the 4-1000 needs a lot of plate voltage (over 5000
volts) to get decent gain. At 5000 volts, expect to drive the tube with
120-140 watts to get 1500 watts out! Expect a "hard to drive" amp unless
there is a a lot of high voltage.
With anode voltages above 4000 volts, the tube gets pretty unstable. The grid
leads are very long, so the PA can develop parasitic oscillations below 90
MHz. The closer the oscillation to the operating frequency, the harder
parasitics are to cure. The 4-1000A is one of the most unstable tubes I can
think of, besides 811A's and 572B's. .
>What about replacement costs?
That's where a 4-1000 shines. Cost is cheap, even if finding a good tube is
Even though IMD products won't be as good as with tubes designed to be used
in grounded grid, but they'll be very livable if you tune the amp correctly.
>(I don't wish to violate Part 97, just run RTTY conservatively)
A GG 4-1000A won't violate part 97 unless the HV is *real* high or you have a
FT-1000 driver! It also won't run RTTY conservatively at 1500 watts because
the plate dissipation is only 1000 watts. At 60 percent anode efficiency (if
the PA can manage that) the tube will be right at it's limit on RTTY and
glowing a pretty orange color!
We have here at our club station a dual 4-1000A amp and has
worked well over a long period of time. It is not a cheap
amp to run - 300/400 watts of filament power alone. We run
about 5000 volts on the anodes.
We had problems with the shadow region(14-54mhz) and thus
converted the pi-network to a series pi. The amp is used
on 160 most of the time. We have many other amps for other
The drive we use is about 100 watts or so. They take a lot
of drive. Gain around 10.
We have another amp that runs 2 3-1000Zs in parallel and
takes about 45 watts drive. Same on the pi - series.
The amps here are very large, takes gobs of air to keep them
The 4-1000As are NOT cheap if new. Check with Eimac and/or
Richardson(distrib) in Chicago - they are not cheap. Our ex
with used tubes has been very bad. Buy one at a hamfest? No
way! How would u know the condx? Hams today are far less
honest about this stuff and you will regret it unless the guy
agrees to take it back.
Operating conditions determine the tube capabilities.
In CW class C, grid driven, with screen voltage applied
the 4-1000 will put out legal power with 3000 volts on
the plate or as much as 3400 watts with 6000 volts. It
will do this with 15 watts of drive. With 20 cfm airflow
and an Eimacv socket/chimney you can run it key down all
day with the above condx.
In AB2 (SSB) it takes 4 KV to get legal power out, grid
When operated grounded grid,, it needs 4KV or more to
get legal power out and the drive level is quite high.
Around 150 watts as I recall.
In the mid 60's I built my own 4-1000A amplifier using
scrounged parts. I tested it on 80 meters and found out
I could pin the Drake W4 wattmeter ( > 2000 Watts ) into
a dummy load. The efficiency would drop down on the higher
bands, but it could generate over 1500 Watts on 10 meters.
My design used a 5KVA pole transformer (pole-peg) and
full wave diode bridge rectifier. If I remember correct,
it ran about 4800 V DC full-load on the plate. The filament
of this tube runs over 100 watts and in the grounded grid
configuration required lots of drive ( > 100 Watts ). I
was using a Drake TR-4C which could easily deliver over
200 watts of output power to the amplifier.
My amplifier had a band-switched tuned input to match
the transceiver to the amplifier. This helped lower the
RF drive requirements. It also used a hefty squirrel cage
blower to pump the air through the socket/chimney/tube.
Here's the area's I would pay attention to when looking
for any amplifier you want to use in RTTY contest service:
1) Low RF drive requirement in order to run your
transceiver on low power. Look for the RTTY
specs in your owners manual, most transceivers
are not rated for 100% RTTY duty cycle at full power.
2) A tube or tubes with 1000 watt plate dissipation and
the appropriate socket & chimney air flow system.
Many tubes die because the glass seal fails when the
pins become overheated. The RCA/Eimac tube specification
sheets list airflow requirements and maximum seal
3) Properly engineered tank circuit and band-switch assembly.
If it is not properly designed, the RF circulating tank
currents can destroy the coils and band-switch. This
happened to me on my first attempt (I actually melted
the coil-form into a puddle in the bottom of the RF deck!).
4) HV bleeder AND safety interlocks on the cabinetry. You
do not get a second chance with these voltages! I also
had a bleeder resistor failure in one of my amps. The
interlock safely discharged the HV in this case!
5) Documentation. There were many good amplifier designs
in the ARRL Handbook using the 4-400, 3-500, 3-1000, and
4-1000 tubes back in the 60's and 70's. As long as the
fellow building these units didn't compromise on the parts,
the amplifier would operate just fine.
To answer your capability question, a 4-1000 amplifier can
easily output 1.5 kW on RTTY/SB/CW if you deliver the required
RF drive. The amount of drive needed depends upon the amplifier
design, so you will have to ask the owner about this.
I am not sure of current replacement costs for a 4-1000A tube.
An indication of a "soft" tube is excessive RF drive required to
drive it and less than full power output. A good tube in a good
amplifier design will run more than 50% efficiency.
Here's a guideline for you:
Multiply the keydown DCV times PA current and divide by 2.
(4400 VDC X 600 mA = 2640 Watts input)
(2640 Watts input / 2 = 1320 Watts ouput)
You should expect 1300 watts minimum output if the tube and
amplifier are "up to snuff". If you can view the 4-1000 tube
when it is run at full output, the plate element inside will
glow a bright red/orange in color. You should not see any, or
very little, blue glow around the inside surface of the glass
If there is excessive blue color or the plate runs yellow or
white, it's time to turn this 4-1000 into a lamp!
I hope this information helps you. I see Tom, W8JIT confirms
much of my experience too.
I am replying privately because I will make some comments at the end
about operations I have seen but do not condone. Given both the humorous
and not so humorous discussion of power that has been going on ad
nauseum, I don't want to fan the flames.
I used to have a 4-1000A amp in the '60s. Real rugged but at 4 kv
limited in output.
The tube is easily capable of 1500 watts RTTY/continuous output under the
proper conditions. Most of what W8JIT and K0RC say is right on the mark.
I would make a few comments -
Plate dissapation is rated at 1 kw with only 50 cfm of air going by the
seals. The real limiting factor is the glass to metal seal in the base.
If you run substantially more air - a big squirrel cage blower - that
limitation is reduced substantially. I estimate (tho Eimac would never
admit it) that the plate structure must be good for in excess of 5 kw.
Using the glass chimney designed for that tube/socket, the cooling is
somewhat more efficient as well. Bottom line - for RTTY try at least 200
The tube is low perveance - it needs lots of plate voltage to allow it to
be driven to power effectively. 5 kv is the minimum I would recommend -
you can use more if you have it. You did not say but I assume this is a
grounded grid circuit. Plan on a good 100 watts at >= 5kv on the
plates. Note that the cathode impedance in grounded grid is around 100
ohms so your transceiver is not going to like the load unless you use a
tuner OR a tuned circuit in the cathode (like the SB220 or Collins
30L1). Before you commit to the amp you are looking at, you should see
what a standard 100 w output rice box will do. It might work and it
might come up a little short.
How to know if the tube is any good? Look at the idling current (so long
as the tube is not cut off by Zener or other bias when not being
driven). Idling current should be 20 ma per kv so long the plate voltage
is 4kv or more. Don't worry about the color. They run orange at 1.5 kw
output. The best 4-1000A I ever had had a little blue tinge (indicative of
either gas - not so in this tube - or a little extra emission) around the
envelope. Of course if it's real blue, the tube is probably shot.
As for what the tube will really do? The modern bottles like the 8877
are big time wimps by comparison. They cannot be pushed at all or you're
out big bucks. As an example, I have seen at least 2 amps with 2
4PR1000As, the pulse versions. They both ran about 10-11 kv on the
plates, about 500 cfm of air past the seals, 1 kw of DRIVE, and leaded
x-ray glass in front of the tube [you have to see the tubes when you run
them like this or they're history] to protect the op from x-rays. Both
could run between 24 and 25 kw output. The tubes ran white in the plates.
But the absolute best was a single 4-1000A I saw in California. 12 kv on
the plates. 2 kw of drive. TWO furnace blowers at about 500 cfm each - one
blowing past the seals and the other sucking hot air up the flue and through an
enormous hole in the side of the house. Asbestos sheeting around the
outside of the hole. When it ran, a sheet of flame like an iron Bessemer
furnace shot out the side of the house. Output power? 15 kw - one
tube. And the guy was real active and claimed that he got about a year's
use out of one tube.
So go for it. It's a fine tube - a little squirrely - but at the prices
you can get them for (probably under $100) - it sure beats an Alpha.
Your RTTY service may beat up your driver but not that final.
The 1981 ARRL Handbook lists the 4-1000A/8166 as follows:
Maximum plate dissipation 1000 watts
Maximum plate voltage 6000 volts
Maximum screen dissipation 75 watts
Maximum screen voltage 1000 volts
Cathode 7.5 volts 21 amperes
Typical operation in *grounded grid* configuration:
plate voltage 3000 volts
plate current 700 mA single tone
screen current 105 mA single tone
grid current 170 mA single tone
approx. driving power 130 watts single tone
approx. output power 1475 watts
Typical operation in *class AB2*:
plate voltage 4000 volts
screen voltage 500 volts
grid voltage -60 volts
plate current 1200 mA
screen current 95 mA
approx. driving power 11 watts
approx. power output 3000 watts
A friend of mine, AA6GK, has had a 4-1000 homebrew amp for 25+ years.
Based on my experience with his amp, I would concur with the other
replies to you that appeared on the reflector, i.e., can be unstable,
plenty of power output available, and takes >100 W driving power in
grounded grid. The driving power was not as much of a problem back
when the transmitters were a pair of 6146B's or better.
Hi Brian ...haven't tried RTTY but i use a single 4-1000 in single-band amps
on 160m and 10m and have found them to be very rugged....full-bore
contesting (lots of cq'ing!), and frequently with high SWR antennas (like
when running at 1.9 mhz or 28.8 mhz)...
have had these amps 10 years with same tubes...and the amps were probably
built in the '50s...likely using the original tubes!...
The grid driven amp was abandoned in amateur service due to drive power,
stability, complexity and cost reasons, in spite of what manufacturers and
salesmen of tetrodes would have us believe!
Amplifiers using grid driven tetrodes cost more to build, are harder to
build, and are more critical to tune and operate than a GG triode PA. The
ONLY thing you save is tube cost. In my mind, saving a few hundred bucks on
the tube isn't worth the risk of not getting a replacement if anything goes
wrong with the sole manufacturing plant in Russia. If it was a pin for pin US
equivalent, that'd be one thing. But a unique tube with a unique socket and
all those complicated voltages to re-design? No way. Not for me.
>I always thought that screen grid was added for
>additional stability and therefore tetrodes can be grid driven with light
>neutralisation if neccessary.
Actually the grounded grid amp has the same advantage. Tetrode's like the
Svetlana are a good stable design, but large glass tubes like the 4-1000 are
terrible! The leads are just too long.
>That's the way we do it here with up to 4 (four) QB5/1750 and 100W drive
required. >Svetlana also proposes such a design with
>4CX1600B or 2x4CX800's and it works for ETO 91B...
I have used the same system with tubes like the 4CX5000 and 10,000, but only
when many kilowatts are needed with low drive. If the power gain requirements
are moderate (perhaps under 50 times), grounded grid tubes are a much better
Why add complicated screen and bias systems with protection circuits, and
make the amp more sensitive to tuning, just to save a few bucks in tube
cost? If I had a five watt exciter I'd used grid driven, but not with a 100
watts or more. If I was hell-bent on a low gain tetrode I'd at least use the
Collins 30S1 circuit, it offers far better performance than a resistor
Dave, one minor point on the old W0SYK designs (there were two:
The Bib Bomb 73 Magazine May 1965 and The Mini-Bomb
73 Magazine May 1969) which were popular in the St. Louis
area in the 60s and 70s. Both designs DID use bifilar chokes in
the cathodes, which is required for the isolation of RF from the
filament transformer. What was eliminated was the matching
network normally required to match the desired 50 ohm input
to the cathode, which is in the neighborhood of 105 ohms for
a single 4-1000. By paralleling two tubes this was reduced to
approximately 52 ohms which made a nice match for the
exciter. But there is a penalty for eliminating this matching
network. The RF ground for the tubes is now returned through
the exciter, making cable length and tuning of the exciter an issue.
The results are an increase in IMD and, sometimes, in unstable
tuning. It is a much better design to include a return path for
the cathode within the amplifier. Doesn't take much of
a network, either L or pi will do and the Q can be as low as
2, so there should not be an issue of tuning the input. Lower
IMD will result, making for happier neighbors on the crowded
bands during contests and it will be somewhat easier to drive
----additional notes on grounded grid operation----
The 4-1000 is a good tube in grounded grid but just doesn't
have the gain of a tube designed for gg service. But stability
can be an issue on the higher HF bands due to the normal
resonant frequency of the screen grid and its phase shift
that results in a tendency for positive feedback near the
bottom end of the FM broadcast band. This can be reduced
by adding a little inductance in the ground lead of the screen,
thereby reducing its frequency a bit and producing a phase
shift that tends to reduce the tendency for oscillation.
Just grounding both the grid and screen in the 4-400, 4-1000
series tubes resulted in the grid hogging the current and limiting
the tubes capabilities. A technique to provide better division
of current between the grid and screen in grounded grid is to
tap the grid connection down on the filament choke. This results
in some RF being applied to the grid as well as the cathode and
the tube will have a better balance between grid and screen
currents. The penalty is that the tube takes about 30% more
drive for the same output. Grounded grid operation of the 4-400
and 4-1000 was so popular that Eimac designed the 3-400 (later
the 3-500) and the 3-1000 (and now the 3CX1200) specifically
for use in grounded grid. These tubes are better suited for gg
operation, but it is hard to beat cheap, surplus 4-1000s for
performance and cost, even if a much higher plate voltage
is required to got reasonable gain from the 4-1000. Anything
less than 4-4.5 KV will provide poor gain and run the risk of
damage to the tube from excessive grid and screen currents
I designed and built a single 4-1000 Amp running in class C for exclusive CW
use on 20M back in the 60's. Running at 1KW input, it put out about 700
watts and the plate never glowed more than a dull cherry red.
The tube should put out 1KW on RTTY (If you have the power to drive it) all
day long and last forever with the tube being adequately cooled. Adequately
means using the Eimac air system socket and chimney with lots of forced air.
(not a fan blowing on the tube)
My guess, is the limiting factor would be the power supply. My power supply
was a monster that weighed a couple hundred pounds. It used 866 mecury vapor
rectifiers in a full bridge, hefty plate transformer, swinging and smoothing
chokes and huge oil filled capacitors. (All of that for 1KW input!) The
4-1000 was designed to run at a very high plate voltage - think around 5kV
I "gave" my amp away with a spare new 4-1000 tube for $100 in 1977 --- The
thing was simply just to big to be dragging around the country, made to much
noise and generated to much heat.
If you intend to run RTTY during contests and other high duty transmitting
the 4-1000 amp may be worth grabbing. And if heat and space is not a
consideration - buy it anyway if it is under $300 -- It would is probably
worth $500 if it has the Eimac air system socket, B&W Pi-Network output, and
a spare tube.
We have several 4-1000 amps at VE7ZZZ. Assuming the amp is designed
well and has adequate cooling you should be able to run the legal
limit for RTTY for days on end. (That's how we run them.)
I believe that the technique of tapping the grid up on the cathode RF
choke provides some negative feedback which is why the stage
requires more drive when operated this way. The stability issue is
pretty much taken care of by the well grounded screen. Negative
feedback typically improves IMD but the IMD varies enough over
the entire operating range of the tube that making generalizations
based on making measurements near a cusp on the IMD curve
may lead to the wrong conclusions about how great the improvement
Operating a tube such as the 3CX300A in super-cathode-driven
service compared to grid driven service can improve the 3rd order
IMD from -27 dB to -46 dB and the 5th order from -36 dB to -49 dB.
Quite an improvment. I don't have data at hand to show the
improvement for tubes such as the 4-400 and 4-1000 but it
should be comparable. Of course the improvement of super-cathode-
driven service over regular cathode driven service won't be as great.
Adding grid and screen supplies increases the complexity and
will move the operating conditions from the Class B region to the
Class AB1 region. Power gain is essentially established by the screen
voltage and static (resting) plate current is set by the grid bias.
So a simple variable screen supply can be added if a variable
gain amplifier stage is desired.
The super-cathode-driven technique is probably a more important
option for the 4-400 with its more fragile grid and screen than for
the more rugged 4-1000. Tapping down about 1/5 of the way from
cathode end of the cathode RF choke should be about right. For
a tetrode there should be no stability problems but I don't think I
would try this with a triode.
Info on Semi- and Super-Catode-Driven Amplifiers is available from
QST p 34 July 1967
Ham Radio p 73 Nov 86
Ham Radio p 43 Feb 87 with a minor correction in HR p 50 Apr 87
I mentioned that Tom and I had taken the 4-1000
super cathode topic off-line and I received a number
of letters wanting to know what the conclusions are.
(Or they wanted to be added to the QRO-reflector if
there was ever such a thing!) So, rather than writing to
everyone that inquired, I thought the following summary
would be adequate.
1) Eimac and Eimac emplyees have referred to the
technique of driving the cathode with some additional
drive to the grid in a limited amount of literature. Claims
were made about improvements in IMD. It was never
a popular idea at Eimac.
2) Tom has tried it and was not impressed. To the
extent that he wished the references would just
3) I have never tried it, I only mentioned the literature
for informational purposes. After the discussion I
continued to look at the problem and I think the
following summarizes the technical issues.
Implementing the technique with the grid tapped
up on a voltage divider from the plate to ground
(ie 30S1) will work for tetrodes in Class AB1 only.
The technique needs a tetrode for the internal shielding
of the second grid and requires AB1 for maintaining a
constant amount of feedback .
If the tube starts pulling any current the VOLTAGE
dividing ratio is upset by the current and the feedback
is no longer based on the ratio of the two capacitors.
Using the technique with the grid tapped down on the
filament choke will not work over the full HF spectrum
due to the varying ratio of the amount of feedback
caused by the variability of the ferrite over frequency.
In an idealized inductor a tap on the choke should
be just like a tap on an autotransformer and the
voltage should be a simple turns ratio problem.
But ferrite rod filament chokes show similar
effects to antenna current baluns consisting of
stacked ferrite cores. The first core does more
work than the remaining ones making for
an unequal voltage distribution across the
choke. And this variation is frequency dependent,
making it impossible to find one tap that is right for
all of the HF bands.
The technique WILL work for a single band amp.
If a ferrite based filament choke is used some
experimentation with the tap to obtain the right
voltage will be necessary.
Eimac published a design based on a parallel
resonant circuit in the cathode (filament) for isolation
and in this case of an air wound inductor a tap based
on the simple turns ratio worked well. But one would
need to switch in different tuned circuits for each band--
something that isn't really very practical.
Simple Summary = NEVER MIND!
>From firstname.lastname@example.org (Matt Trott) Sun May 12 16:15:34 1996
From: email@example.com (Matt Trott) (Matt Trott)
Subject: 10/40 Close spaced stacking
Okay, the glaciers have begun to recede enuff that two weeks ago I finally
got the concrete poured for the 80' 45G. I've been tossing in my sleep all
winter as far as what antennas to put on it. I have a K5RC VERY stout 20'
mast (108,000 psi).
My latest plans (all of these ants are on hand): 205 at top; 402CD 10 feet
above 205; 105 @ 5 or 6 feet above 402CD. (15
meters? sidemount later).
Question: (1) Any experiences out there with close spacing of 402 and 105?
(2) What's the general consensus on pinning the booms to the mast?
What does this do to the integrity of the boom? mast?
AA7BG firstname.lastname@example.org Matt Trott
>From email@example.com (Bill Turner) Sun May 12 17:11:47 1996
From: firstname.lastname@example.org (Bill Turner) (Bill Turner)
Subject: Mother of All Amp Summaries
At 02:49 PM 5/12/96 +-100, Brian Short wrote:
>Whatever was in that ZIP file, it was corrupt when it arrived here, even
FWIW, the file arrived and decoded fine here. Thanks Brian - good info!
73, Bill W7LZP