[Hallicrafters] HT-37 Bias Adjustments

[Bill]

Hi guys,
 
Pulled the top cover of the HT-37 and here are the voltage measurements
for grid bias.
In standby mode, - 49 volts.  Measuring this same voltage in transmit, -
46 volts.  
 
Following advice posted here, I put the rig in MOX and while
transmitting, I attempted
to adjusted the bias to - 49 volts.  Couldn’t get there but I was able
to get to – 47.5 volts.
In standby, the bias voltage is now – 51 volts dc.  This minor voltage
changed has resulted
in a cooler running rig (maybe).  I don’t have actual temperature
measurements, but it
does feel cooler.  I will run temp checks to confirm.
 
Possible reasons for this problem (?).  When restoring the rig, I found
SR1 bad.
SR1 was replaced with a standard silicon diode of appropriate ratings.
Both capacitors
C98 & C99 were also replaced.  When energized, the bias voltage soared
and I could not
get the – 49 volts dc.  At this point, I changed R64 (4.7k) to (15k).
This change
allowed me to obtain the requisite - 49 volts dc at TP2 in standby mode.
It is possible that
I may have to change the 15k to a lower value to be able to get back to
– 49 but I do not
think this will be necessary.
 
Those are the voltage measurements, I will get back later with
temperature changes (if any).
 
Bill (K2WH)