[Hallicrafters] HT-32A finals resting current

[Karin Johnson]

Hi Jeff:

Saw your post on the Hallicrafters list.

It is somewhat subjective given that the datasheet

for the 6293 doesn't give much information about this

tube's use in amplifier service.  If you make some assumptions

that this tube is somewhat comparable to the 6146B then 

that datasheet gives a resting current of 25 ma with 750 volts

on the plate and 200 volts on the screen.  In the HT-32A and B

the finals are not really completely cutoff when not in transmit

mode, so the resting current is there all the time.  I have a simulation

program I helped write that can be used to design linear RF amplifiers

based on the EIMAC tube calculator.  I did some experimenting with

different values of bias voltages with this program and it doesn't really

make too much difference from Idle currents ranging from 20 ma for both

tubes, up to as much as 80 ma for both tubes.  There are some other

esoteric side effects too, like change in tube output impedance which could

affect the efficiency of the finals.  I don't believe it is something to
really

worry about though.    Of course the down side to higher idle current is

more heat generated if you're not in transmit mode.   50 ma sounds about

right given the value from the 6146B and 6146A datasheets.  Using the -49
volt

setting described in the instruction manual would only be really usable if
the line

voltage was within limits given the original instruction manual, and the
original 

tube set (ie: 5R4GY HV rectifier) were in place. 

 

Karin Anne Johnson   K3UU

Palm Harbor, FL