[Amps] Amps Digest, Vol 32, Issue 36

[k7fm]

Rich said:

1. In order to reduce VHF gain, parasitic suppressors need to have a low-Q. 
In your opinion, do Ag and Cu contribute to a low-Q?

2. Even a medium-Q parasitic suppressor is better than no suppressor 
whatsoever.

3. Can you name a commercial HF 8877 amplifier besides the AL-1500 that does 
not use a VHF suppressor?

4.  So Dick Ehrhorn made a mistake in the Alpha 77 by using a VHF 
suppressor?

Response:

1. If an output circuit does not have stray reactances that act as a high 
impedance for vhf signals, and the tube does not have internal stray 
reactances, there will be no vhf instability and no parasitics.  In that 
case, it does not matter if the parasitic suppressor is made of silver, gold 
or pork bellies - except that pork bellies would attenuate the rf rather 
substantially.

2.  The point was that the Al-1500 appears to be proof that any VHF 
suppressor is not necessary.  If it was necessary, then every AL-1500 would 
fail every time it was used, since it does not have what you say it 
requires.

3.  My statement was "Many high power amplifiers used in commercial services 
do not use parasitic suppressors."  I did not mention the 8877, nor did I 
mention amateur amplifiers.  The point is that the 8877 is similar to many 
larger tubes in construction.

4.  I did not say Dick Ehrhorn made a mistake in his Alpha 77 - you tried to 
imply that my statement lead to that conclusion.  Dick Ehrhorn was a 
respected amplifier builder that knew a lot more than I do about amplifier 
construction.  He also put a high power amplifier and power supply in a 
relatively compact desk unit and perhaps the circuit layout had sufficient 
lead length to require parasitic suppressors.  Perhaps he put one in because 
he did not wish to spend a lot of development time trying to do without.

Let me twist the words like you do.  Are you saying that the designer of the 
AL-1500 is stupid because he did not use a suppressor, or in other words, 
that you are smarter than he is?

Seems a bit like all of the scientists that published papers proving that 
man could not fly while the Wright Brothers were doing just that.

Colin  K7FM