[Boatanchors] HARVEY WELLS TBS 50

[Flowertime01 at wmconnect.com]

Jack,

Yes, you could have a parasitic in the final.

It would be best if you could hang a scope, spectrum analyzer, or a VHF 
receiver on the dummy load to determine the frequency. With test equipment it could 
be easy to find and fix.

Some extra caps in the RF finals often help.
If the output is a screen grid tube the screen grid circuit can have some 
extra caps added to move the resonance off the want to be frequency and thus 
quench the parasitic oscillations.

You can try to wind some lead wire into 1/4" dia coils of many 10 - 20 turns 
and insert theses between the bypass caps and the RF leads. The idea is to 
change the resonate frequency of the RF leads and the parts that form the tank 
circuit that is providing the resonance for the oscillation.

Neutralization works if you only have one or two resonate frequencies that 
need to be quenched. If the circuit has several frequencies then you need to add 
parts to deal with some of the frequencies, and then neutralize the rest of 
the frequencies.

Most transmitter problems are from these circuits that have several problem 
frequencies.

100, 47, 27 Ohm resisters over wrapped with copper wire to form a VHF 
suppressor on the plate of the tubes works well. You may need to experiment with the 
coils more than the resistor value.

Some times some 100PF 1000 volt or silver mica caps from grid leads and 
cathode leads can help quench some of the parasitic.

I hope you get some more mail and idea on how to deal with these problems.

Roger AI4NI   </HTML>