Date: Thu, 03 May 2012 02:34:46 +0000
From: Manfred Mornhinweg <manfred@ludens.cl>
Subject: Re: [Amps] Tubes vs. Solid State
- Hams are obviously willing to pay 5000 bucks for an amp, so why
destroy the market by making amps that sell for 700 bucks? The
intermediate option, making amps that are cheap to make, and then sell
them at 4000 bucks, probably won't live long with hams. They want to see
where the cost is.
## I can hb a pretty big tube amp for $5000.00 I can do a really
big one for $7000.00
And another technical problem is that my amplifier probably won't end up
particularly rugged. If you set your mind on it, you can probably blow
it up just by slowly tuning an antenna tuner through its whole range,
until you find a setting with sky-high SWR that just happens to create
high enough drain voltage peaks to fry the FETs. Protection circuits can
keep FETs alive, as long as the high SWR comes up slowly (milliseconds),
but if you have a loose connection in the antenna system, that provides
1:1 SWR most of the time, but suddenly goes up to a condition that
causes those high voltage peaks, this amplifier can be blown up more
easily than one that uses just a few, rugged FETs. The reason is that
I'm using many small FETs, directly in parallel. That's simple to do,
and inexpensive, but any overvoltage will make a single FET enter
breakdown, and that single FET cannot survive the big discharge. When
using just a few large FETs, which is much more expensive, the big FET
that breaks down has a much larger chance to survive.
### Aside from all the typ problems of SS amps, there is even more
problems. None of em will run full bore rtty, etc into a 3:1 swr !
So now you require the mating automatic 2 kw CCS rated tuner.You
don’t need the auto tuner with the tube amp, not mine anyway.
5 kw CCS rtty into a 3:1 swr....no sweat. Lets do lunch.
## With these SS amps, you also require a monoband 2kw CCS
rated LP filter for each band ! At least a min of 5-6 required
to cover 160-10m + warc. Plus you have to be able to switch
them in and out.
> As to home brew, there are very few of us who actually do that be it SS
> or tubes.
I can't help it, I worry that this is spelling the end of ham radio. To
me, ham radio is about being interested in radio technology. I can
perfectly well accept the fact that not all hams are professionals in
electronics, but I would expect that all hams, without exception, should
at least be interested in electronics, and try to learn, at their own
rate. I just can't understand those people who say they love ham radio,
but whose love for radio ends precisely at the front panels of their
rigs! To me, they DON'T really love radio. Instead, they are after the
utilitarian side of ham radio, such as keeping in touch with friends and
family, or having emergency communications. In my surroundings, at least
90% of hams, and probably much more than that, belong to this group that
doesn't have any interest whatsoever in electronics. Hear them talk on
the bands: The weather, the brand and model of their rig and antenna,
and that's about it. I call them "empty QSOs".
### ham radio is in its dying years. They hand out ham tickets
like popcorn, and they still cant give then away. Empty QSO’s,
that’s at least one step better than 10,000 brain dead contesters
on every 2nd weekend.
Of course, anything like that is too complex for the "typical ham", the
one at whom the ARRL is addressing QST. But even the simplest tube type
amp is neither for the typical ham, because that typical ham would never
dare to build anything having 3000 volt in it. Or rather, he would never
attempt to build anything at all, period!
### You may be right. No such thing as a slight electrical shock
with HV. Take all precautions, and its not an issue. My hb RF decks
are separate from the HV supplies. Each box that has HV or B+ inside
it, gets it’s own dedicated HV meter...wired directly between B+
and B-. If the B+ HV fuse blows open in the rf deck, the HV meter
in the rf deck reads zero. Mean while the hv meter in the HV supply
still reads full B+. The whole issue when dealing with hv is rather simple.
You have a better chance of getting mashed in your car by a soccer mom,
trying to do some texting while driving vs HV accidents.
> I still maintain SS is not ready for prime time, but for those with the
> knowledge and desire to experiment it's a great field.
Well, I think differently: I think solid state is the way to go,
definitely, at the power levels hams are allowed to use.
#### How am I supposed to get 750 watts AM CXR, and 3750 watts
pep out.... and measured at the feed-point of the antenna..with
SS. Almost forgot.... that’s into a high swr. Repeat for all bands
160-10m, including warc.
Only at much
higher power levels do tubes make real sense. Simply because tubes are
available for several tens of kilowatts in a single device, while
transistors are not, and would need to be stacked up in too large
quantities. But at 1.5kW, and even 10kW and some more, solid state is
more practical than dealing with tubes and their inevitable
narrow-banded tuned circuits, their lifetime of a few thousand hours,
and sockets costing a thousand dollars!
### say what. A typ 3CX-3000A7 will last 4 years at full CCS
output. That’s 35,000 hrs...not a few thousand hrs. I use a regulated
AC Sola constant V xfmr.. that feeds the input of a variac... that then
feeds the input of the fil xfmr. The new Tube is run at rated fil V,measured
at the socket for the 1st 200 hrs. After 200 hrs, fil v is reduced to the pint
where the Po just barely drops off a few watts, then the fil v is increased
by .1 or .2 volt. As the emmision wears down, the fil v is raised up by
.1 v. When I end up with the fil V at +5%..then send it in to be rebuilt,
for half the price of a new tube. The socket for a 3CX-3000A7 is cheap.
The YC-243 has no socket. GG triodes dont need sockets anyway, nor
does the YC-156. Just bolt the grid flange to the chassis..done. The
F7 version of the 3CX-3000A7 also does not require a socket. Heck,
they even make a water cooled version of a 3CX-3000A7.
One could argue that a lifespan of a few thousand hours for a tube will
last a ham's lifetime of normal operation. But practical experience
shows that tubes are less reliable: Among the local hams I know and who
own power amps, the spread is about 2/3 tube amps, and 1/3 solid state,
changing fast to increase the proportion of SS. Most of these hams turn
to me when something fails. Over the last several years I had to replace
several 3-500Z, and a few other tubes, but not a single high power
transistor.
## I know folks with SB-221’s who are still getting full PO
from the original tubes. I have replaced one pair of tubes
in my drake L4B linear since I bought it new, back in 1977.
The only time I got a solid state amp for repair, a Quadra
that had seen extensive contest and DXpedition use, the problem was a
broken solder joint that took five minutes to find, and one second to
repair.
In several tube amps I had to replace electrolytic caps, and I had to
rewind two power transformers. In SS amps, so far I have seen no power
supply trouble. Of course, the number of amps that could possibly fall
in my hands when broken is small, but I believe that it's enough to do
at least a broad statistic about their reliability.
### What is the TX IMD on these SS amps you have built.
That Elecraft K3 xcvr is crap at -29db IMD-3. I don’t think
their KPA-500 is much better.
Years ago I looked into the possibility of making broadband tube
amplifiers, because I just hate having to retune an amp after changing
bands or even changing frequency a lot within a band. But I quickly
found that the tubes' combination of high internal capacitance and
required high operating voltage makes this totally impossible. Tubes
force the use of tuned circuits, while transistors give the designer the
choice between tuned and broadband impedance matching.
### Using 3-4 x drake L4B amps, all wired nose to tail in series,
(since they will handle 2 kw on bypass mode), I just tune each
one up on a different band ! One rotary switch ensures only
one key line is active at any one time. Simple.
## the hb 3CX-3000A7 amp and also the YC-243 amp uses
vac tune and load caps.. + a pair of broadcast variables for the
tuned input. Separate bandswitch for the tuned input and high
power Pi net. Each vac cap gets its own turns counter..which reads down
to .01 of a turn. The pair of broadcast variables get a 4 inch diam, jackson
bros
ball drive, which is calibrated 0-100 over a 180 deg arc = 6 inchs.
## it takes exactly 45 secs to qsy from 15m to 160m. Just dial up
using pre-sets. 1 pre-set for cw and 1 for ssb on 20-10m. On the
lower bands its 1 pre-set for cw..and 2 x pre-sets for ssb. The secret is
to lower the loaded Q a tiny bit. Even with the drake amps, I tune it
at 14.200 and its good from 14.100 to 14.325 with a flat ant swr.
I cant squeeze any more out of it by retuning at 14.100 or 14.325
so just tune it once at 14.200.
Tube dissipation ratings instead are true, real, directly usable, as
long as you assure enough airflow. This difference comes from the simple
fact that tubes usually have their heatsinks built-in, while transistors
do not, so transistor ratings have to be given in a way that allows
equipment designers to calculate the true allowable dissipation, after
fitting a certain heatsink.
## large metal tubes are easy to cool. Plus they are usually
specified with an IN-take air temp of 40-50 deg C. Now
I put mine in the un heated workshop next door to the shack.
If Im working in the shop, then the shop gets heated. In take
air temp is more like 15-20 deg C. Anode diss goes way up.
Crank up the air pressure, combined with colder air..and it goes
WAY up. I can easily get another 50% CCS anode diss with that
technique. For cw-ssb use, the pressure can be turned way down
of course.
## whether it’s a tube amp or a SS amp... and it makes noise,
just put em into another room. Then zero noise in the radio
room..and no heat either. In winter, heat from the amps
stays in the basement shop. In summer, its routed to the outside.
## My other problem with SS is eff. Your typ SS amp operates at a
lousy 50% max eff..and that’s when run at max output ! Reduce
the PO by half....and eff will drop down to 35%. At that point,
you have to reduce the vdc a bit to get the eff back up. The
problem with reduced vdc is.... the TX imd drops off !
## a 1.5 to 2kw output CCS SS amp, that covers all 9 x bands, and will
handle
a 3:1 swr and LOW IMD, is no simple task. Hats off to anybody who can
pull it off at any price. BTW,,, these 1-52 kw SS FM broadcast amps you
see typ
consist of 1-52 x 1 kw SS modules, with mating switching supplies.
Then a myriad of combiners. They operate at up to 92 % eff..and are
NOT linear amplifiers. They operate on a single freq..with a 1:1 swr.
So don’t use them as some kind of reference or standard as to what could
or should be done with 9 band ham type SS linear amps.
## ONE instant on GG triode, no socket, simple un regulated B+ supply with
a
tuned pi input and a pi output is about as simple as it gets. You will go
broke
trying to get YC-156 power levels from SS. Why not back up one notch..and
start
with a LOW imd xcvr that puts out 200 w pep, without going into melt down.
The K3, with its lousy –29 db IMD-3 and 100w pep out simply does not cut it.
later.... Jim VE7RF
Note that some solid state devices, such as many diodes and also some
switching MOSFETs, nowadays are rated for dissipation and/or current at
a more real-world temperature, such as 75 or even 100 degrees Celsius.
> Depending on frequency we set the internal limit at 100C and max
> internal operating temp at somewhere between 70 and 90C.
> dopant migration was starting to become noticeable at 100C so when I was
> in the industry.
That's a bit lower than I had known. Anyway one has to keep in mind that
these phenomena are time-related. A ham amplifier can probably get away
with pushing the silicon to 150 degrees when delivering full output,
because this will only be short-term. If the transistors live for 10,000
hours at that temperature, that should be enough. A broadcaster instead,
running 24/7 at full power, will want to get much more than 10,000 hours
of life from his transistors, and so they need to run cooler.
That said, and having done calculations on the thermal aspects of
widespread ham equipment, I can't avoid the suspicion that many ham
transceivers run their finals well in excess of 150 degrees internally!
The typical max ratings are often 175 degrees or even 200 degrees for
transistors that are NOT encased in plastic. Particularly brave
manufacturers even specify 225 degrees. I don't know how much of that is
due to processing techniques that reduce dopant migration. The rest is
probably based on decisions to accept shorter lifespans as "typical". In
any case, silicon by itself survives much higher temperatures. It's the
migration problem that sets a limit, and the attachment of the chip to
the case (usually by some solder) sets another limit.
> You can also use *cold* or chilled water. Just draw the water out of an
> open PVC tank and return to the same tank. 20 gallons will run a KW amp
> for quite a while. Throw in a few chunks of ice and have at it. We use
> the water in plastic bags for our picnic coolers , so you just grab a
> couple and drop in the tank
But one needs to be always careful about avoiding condensation inside
the amp. At my former job, we had tons of actively cooled electronic
equipment. There were big coolers to chill the water/glycol mixture just
enough to keep the outside of the electronic racks precisely at ambient
temperature, to prevent thermal turbulence. The controllers monitored
ambient moisture, to keep the water always above the dew point.
Sometimes something went wrong, and then we got dripping wet
electronics, with all the obvious consequences.
The coolers were mostly of the plain common compressor heat pump type,
but in some vibration-sensitive locations we decided to try Peltier
coolers. They turned out to be a disaster. The place was at 2600 meter
altitude, the Peltiers overheated due to the low air density, and died
faster than we could throw them in the trash.
> You can take it down as far as you like as long as you don't get
> condensation on the circuit board,
Exactly. And with a typical comfortable ambient humidity of 60 to 70%,
condensation happens at just about 6 degrees below room temperature!
It's not worth doing, for such little temperature difference.
> or ice up the pump.
At any normal room temperature and humidity, condensation will occur far
sooner than any ice can form. The dewpoint at comfortable room
conditions is always above 10 degrees Celsius. You would need an
extremely dry or very cold environment, to get the dewpoint below freezing!
> BTW there is a fungicide used in swimming pools that will do a good job
> of keeping *stuff* from growing in your cooling system. I'm not
> referring to Chlorine.
I will have a look in the swimming pool section of the home improvement
store! Thanks for the hint!
Manfred
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