[Heathkit] problem wit a HW-32a going into oscillation.

[Glen Zook via Heathkit]

I don't think the ground problem is the cause of the squealing in the audio.

In the Collins 75S- series receivers, there is a 100 mfd electrolytic capacitor from the cathode of the audio amplifier (not the audio output tube) to ground.  When that goes bad, there will definitely be oscillation as the volume is increased.

In the SB-101, there is a similar capacitor from the screen of the audio output tube to ground.  This is a 20 mfd, C-304, connected to pin 3.  I haven't run into this particular problem in SB-Line.  However, based on my experiences with the Collins 75S- series, I believe that there is a very good chance this capacitor is the source of the problem.
 
Glen, K9STH 

Website:  http://k9sth.net


On Thursday, October 9, 2014 9:57 PM, Chuck Penson <wa7zze at gmail.com> wrote:
 


Make sure you have the HP-23 power supply set to 250 volts, not 300. These things do not like to run at the higher voltage setting. 

Chuck / WA7ZZE

> On Oct 9, 2014, at 5:34 PM, wt4t at reagan.com wrote:
> 
>        Picked up a 32a today, cleaned all the contacts,pots ,tube pins etc. powered up the the rig,seemed to work for about 1/2 minute then broke into oscillation and has stayed there since. The manual suggests replacing the c-121 ,so I did that ,same problem. the bias will set correctly and the rig shows output when keyed. the oscillation continues with the two finals removed and the driver. anybody point me in the right direction, before I start readings of the system voltages ,point by point,per the manual. 
> 73
> dale wt4t
> 
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