Well, I've finally got this amplifier working back to spec. The parasitic
oscillations are gone, output is 500+ on 80 through 15, and just about 500
on 10. All levels are with 70 to 80 watts in. There were a whole bunch of
things wrong with it:
- Parasitic suppressors were around 85 ohms
- 33 ohm grid resistors were fried
- 10 meter input coil ferrite slug was broken (overheated?)
- 1 tube socket was oriented 90 degrees, which left the filament in a
horizontal position (I thought these tubes could be oriented in any
position?).
- Grid caps were out of range
- I had ZERO knowledge when I started this
... I may be missing something else, I've done so much! I believe most of my
problems to be the choice of resistors. I couldn't find 2 watt 47 ohm and 2
watt 33 ohm resistors at the popular distributors, so I chose metal film
instead - WRONG!!! I don't have sophisticated test gear here to see what was
happening, but there must be some inductance in the resistors I tried to use
which threw off the whole amp. I even tried "newly designed" suppressors for
the amp, but they wouldn't work. If there's a carbon comp resistor you want
to replace, use the same thing to keep the amp happy.
I've learned that if you are having problems with your amp, replace
components with EXACT replacements unless you can adjust component values
for anything that may change. This amp was designed by intelligent people -
no need to change anything since it's a proven design (unless you're making
a conversion).
I want to thank all of you who responded to the questions I had - this
has been quite a learning experience for me, and I'm glad I'm through with
it! Now it's time to just use it! It was almost too much for a beginner like
myself. I wish everyone here a pleasant & safe holiday season. 73's... Larry
N1MIW
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