> I have been around a lot of amps ..... Every amp that had a parasitic
>blowup episode used a 3-500Z . I'm talking TL -922 , SB-220 , AL 80 , AL
>80a ,AL82, SB-1000 , Drakes, Viewstars & more ... If it has a 3-500z
>....it WILL someday hand grenade, I had two go off next to me , my friends
>SB220 & AL80.... blowing parts everywhere & dreaded grid to filament
>shorts.......I have no confidence in that tube. Every time I use an amp with
>a 3-500z in it , I am waiting for the big bang .....
I too have had stentorian parasites at 110 - 120 MHz with the 3-500Z.
However. there is a method to reduce the VHF gain of the tube --
providing one can tolerate a 2% power reduction at 29MHz: That is:
Reduce the Q of the hidden VHF tuned-circuit between the tube/tubes and
the Tune-C. This can be accomplished with lower VHF-Q suppressors.
- The 3-500Z has a reputation for parasitic oscillation and it has
0.15pF of feedback-C. However, 2, 8877s have 0.2pF of feedback-C and
they have roughly twice as much VHF-gain. Thus, 8877s are hardly
fool-proof. . . . Murphy was right.
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,