Tom wrote:
"the opposite is true. Example -- With higher Mu Amperex tubes in a
SB-220, the 5V bias zener needs to be shorted (0V) to increase the ZSAC."
The published data sheets as per the Richardson , state that the
amplification factor for current Amperex tubes is identical to late
production Eimacs, as per the earlier post here.
The amplification factor (represented as µ) of a tube is equal to the ratio
of a change in plate voltage to the change in grid voltage required to cause
the same change in plate current. These tubes are identical in this respect,
and if you need to short the zener, could there not be another reason?. Are
you suggesting that
the Richardson sheets are incorrect?
The earlier Eimacs, 1968 vintage, were actually higher mu than the last
production, or so the data sheets say.
Most people report that the Amperex tube is an excellent drop in replacement
for the Eimac. I have never used them myself because of the very high cost.
In any event
I like to replace the bias zener diode with a string of silicon diodes, and
adjust the bias voltage for about 160 to 170 mils of indicated idle current
for the pair of triodes.
73 and Happy DXing,
Mike
W2AJI
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