Curt -
I still like the transformer! :-) 240 ohms is the correct DC
resistance of the primary, but a shorted turn or other _AC_ anomaly is
what I suspect.
Couple more things to try. First, measure the actual resistance of
R43. Then, measure the voltage drop across R43. Calculated current
should be about 35 mA, which would correspond to the current indicated
by 3.5V across the 100 ohm cathode resistor. There is approximately
0.4W left in R43, which doesn't leave much room for excess current.
If you have a small 6.3V filament transformer, you could sub it for the
output transformer.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>
Curt Nixon wrote:
I am stumped by an issue with my old trusty R4A. The audio amp, 6EH5
tube is running with a red-hot plate.
All of the DC voltages look good and there is no input signal except
the real one when the gain is advanced. There is a very large (5V
P-P) on the output side. It is low freq (120 hz.
The radio has new electrolytics on main and bias supplies and I tried
replacing the polarized tubular decoupling caps in this stage to no
avail.
I saw the note about anti-vox oscillation in the R4B tech notes and
tried that but no change.
About the only thing I havent tried is the audio transformer. the
primary reads about 240 ohms.
The audio out from the speaker is about half what it should be.
Any suggestions?
Thanks,
Curt
KU8L
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