Hello again,
First off, I want to thank everyone who responded with offers on my
request for the k9lka 4-1000 amplifier article mentioned in the recent
posts.
I received a fax from Alan with the article. If one of you who offered a
scanned image would be so kind, my alter ego Email address of
skipp@pilot.ucdavis.edu will take your attachments just fine. Let me
thank you ahead of time for your help and kind offer.
I have a quad mono band set of 4-1000 amplifiers I built in the early
80's using surplus aircraft style metering. Sure looks wacky to the
untrained eye, but you can't deny the end product. Maybe a digital photo
on my sonic server web page is in order.
I keep flashing back to my old Piper and want to land the thing "short
field".
There are some significant differences with the article vs "my" final
design. I will admit much of my circuit was "lifted" from the various
diagrams I have, taking in all the best upgrades.
After the initial project/hardware was completed, I added circuit
improvements, a number of them provided by Rich in conversations on 40
meters in the "war zone."
1) Grounding the grid with large straps direct to ground and metering the
grid and plate current in the filament transformer lead. I was never able
to get the grid metering to stay stable when the grids were anything but
strapped to ground. Might have been my network, but various combinations
never boar stable fruit.
2) Reducing RF hash in the receiver with a higher value cutoff resistor.
The original 10K 10 watt resistor didn't completely cut off the tube. I
ended up using a 47K 5 watt resistor. Even low values of Ip were the
source of receiver noise problems with my higher plate voltage (vs the
article).
3) These amplifier always seemed to have large amounts of grid current
and somewhat erratic plate current. The 7.250 Mhz stage would hose not
only my HF receiver, but take the local six meter Icom 551D for a ride
with large bursts of "noise" swishing around 54MHz. I used to attribute
the 551d.
The increased value cutoff resistor took care of the 7.250 hash.
About that time, I installed my own design of suppressor using the same
type wire Rich includes in his kits. I think I even used one of the SB
200 Kits he sold me for the wire, just my own larger resistors.
The results of the 40 meters deck retrofit were immediate. The grid
current reduced to more realistic values, the Icom 551D became silent
during legal limit 40 meter operation.
I share one heater transformer per pair of tubes and switch HV.
Designed that way, more by fate than intentions.
The quad mono band amps are still here, idle for the time.
Onward...
[snip]
:Hey, I noticed a new descriptor here. The freshness of the Eimac Red
paint.
:Next thing you know, people will be spraying new paint on their tubes,
and
:applying like new Eimac decals.
I didn't see the Eimac label, but RCA, GE and many others were there. At
a local flea market in Sacramento, a "Vender" was selling new tubes in
white box's. Most were of the audio type (6L6, 6550 and EL34), but there
were some smaller glass rf types.
The paint was barely dry on some... After mentioning my projects in
process, the seller mentioned all the tubes were from China or Eastern
block countries and he put the labels on himself (easy to tell). He
offered a distribution price for large quantities.
He would supply bulk quantities with any label requested... the best bet
was the lifetime quality control warranty he gave.
After one flea market, he's never been back to the many in this area. A
lot of people were around for the next meet, carrying white tube box's.
Audiophile friends of mine have had nothing but serious problems with the
asian produced tubes. Often mechanical failures occur. One a month ago
took out a mint Dyna ST 70.
:What about the smell of a new tube, is that important? Personally I love
:that odor of baking in a new air cooled tube. Water cooled tubes don't
cut
:it for this aroma.
No, the reverse... If I just paid big bucks for a tube with handles, I
just want it to sit pretty and make RF. If somethings cooking too much,
I'm throwing the switch to standby. Water cooled tubes could be used to
make hot tea...
:Then there's that smell of a new Heathkit being fired up the first time.
:Remember that?
Electrolytic flying across the room.... sure I do. (just kidding)
:John
:K5PRO
cheers
skip may
wv6f
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