Congrats to Jon, KE9NA, on the 4-1000 amp. Hey, if it works like you said,
don't ask questions, just knock on wood, good job! I am surprised that the
series L in the plate connection didn't just move that 80 Mhz resonance
that you've seen in the past, down by 10-20 MHz. You said there is no
noticeable dip from 50 to 150 MHz.... What about just below 50? I am amazed
that there isn't a big resonance due to the L and the first tank C, or the
tube output C and the L and first tank C to ground.
In my TH555A grid driven 100 Kw amplifier last summer, I had a huge
resonance at 41 MHz, and was running at up to 6 MHz. I fretted over it, and
even built this super suppressor, with globars and a chunk of ferrite, but
it wasn't needed. The amplifier would not take off at 41 MHz. I believe
that the screen bypassing was adequate, and the feedthu component from
output to input inside the tetrode was not of the right phase to support
positive feedback and oscillation. Plus that the input was well tamed and
shunted with 100 Ohms, and the cathode bypassing was good up to many MHz.
Yet, on a GDO or network analyzer, whammo, big high Z at 41 MHz. It was
found to be the tube output C, the copper strap, and the Comet vacuum cap
to gnd, (the tuning cap for the Pi). This cap was acting inductive at this
freq I believe. With it shorted, the freq of the potential parasite-causing
parallel resonance would shift in freq.
> IMHO, my theory on the "L" coil adding to the stability
>was correct. It completely looks like a very large reactance to any VHF
>energy. And when checking the anode circuit with a dip meter, I could
>not find ANY noticeable dip from 50 to 150 MHz. With all my previous
>anode/tank circuit designs, I had a nice dip about 80 MHz. The resonant
>capability of the circuit at VHF is gone.
So when I read your observation, I think that it is still somewhere, just
that you moved it. And your jug just doesn't want to oscillate there! I
forget if you are running grounded cathode or grounded grid? Whatever
you've done, consider yourself blessed, and go on to bigger and better
things. Maybe will hear you on HF.
John
K5PRO
New Mexico
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