>
>In the absence of obvious failures like tubes don't glow, tubes glow too
>brightly and make loud noises, foul odors or trips breakers, what
>indications would lead you to retube a 3-500Z amplifier?
>
Won't make 400mA per anode when fully driven =s weak emission. The good
news is that weak emission means less ability to oscillate. // A
fil.-grid withstanding potential of under 5kV indicates a bent filament
that is on the verge of shorting to the grid.
>In my case, it is an 18-year old Henry 3K-A with the original finals.
>
I know of one case in Santa Monica, and one case in Huntington Beach,
where 3K-A amplifiers grid/fil. shorted two pairs of new tubes in under
1 hour. [sic] High anode potential with frisky new bottles delivers
maximal VHF gain. Reducing VHF gain before installation of new tubes in
a 3K-A is probably not a bad idea. / Other problems: There is no
glitch resistor in the B+ circuitry. / There is a c. 95MHz resonance in
the HV-RFC. A ferrite VHF-attn. bead is needed at the top of the choke.
/ The meters need glitch diodes. / There is an enclosure resonance
that is close to the oscillation frequency.
cheers, Hank
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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