On Thu, 11 Sep 1997 10:05:20 -1000 STAN <KB8JLV@worldnet.att.net> writes:
>I have an ameritron AL-80B that I am replacing the tube in. I have an
>Amperex 3-500 (NIB) I would like to use. Is this tube a suitable
>replacement or is there some modifying that needs to be done to use
>it.
>Stan/KB8JLV
Amperex tubes have a bit higher mu which could make a marginally stable
amp unstable. You will get no more output power but you may reach that
point with lower drive.
The first thing to do would be to set the idling current by Amperex's
spec sheet...not the amp info. This may require changing the bias circuit
a bit. Once that is done the Amperex should perform well.
An almost painless way to modify the bias circuit is to replace the zener
with a series string of 7 to 8 1N5408 diodes (actually anything in that
series is OK). They must be reverse connected but you can tailor your
idle current by shorting out one diode at a time. This is not a perfect
solution but sure beats buying a bunch of expensive zeners to experiment
with. There is loads of room in that amp to install a hunk of perf board
with the diodes.
73....Carl KM1H
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