[AMPS] KE9NA's successful PA

[Jon Ogden]

>
>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.

When measuring the anode with the dip meter here is what I saw 
(approximately, it's been about a week since I measured it):

Resonance at 28 MHz - tank circuit was tuned to 10M
Resonance in the high 30 MHz range - plate choke
Resonance around 50 MHz - yes this could be the anode, but I think it is 
the resonance in the "L" coil.

Circuit is completely clean and clear of resonances from 50 MHz until 150 
MHz.  In the past a rather good resonance could be seen around 80 MHz.  

So perhaps I did move it lower.  Whatever the case, the amp is stable.  
And I tried the stability test of keying the amp with no load and moving 
Ctune thru its entire range.  

AG6K's cathode suppressors did work very well.  W/O those, the amp was 
not stable but oscillated easily.

Someone pointed out to me that an oscillation can occur in an amp when 
there is a low reactance from the anode to ground.  With the "L" coil in 
place, it has such a high reactance at VHF, that the anode won't see a 
low reactance to ground.

>
>> 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!

Well, correct.  I am not sure where it moved, but who cares!
> 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.

Grounded grid.

Yes, maybe you will!  I've been getting good reports on it.

Thanks for the note.

73,

Jon
KE9NA



--------------------------------------------------------------------------
Jon Ogden

jono@enteract.com
www.qsl.net/ke9na

"A life lived in fear is a life half lived."


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