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[CQ-Contest] Need Help Fixin' Collins Amp

Subject: [CQ-Contest] Need Help Fixin' Collins Amp
From: W5ASP@aol.com (W5ASP@aol.com)
Date: Tue Jun 24 17:30:15 1997
We  are trying to fix an old Collins 30L-1 linear amplifier that had been 
on the shelf at a friend's QTH in the Caribbean, having failed several years 
We have replaced filter capacitors, diodes, tubes, etc., and finally managed to 
it working... sorta...

It works great for about 20-30 minutes, but then the quiescent plate current
goes away.  This suggests a thermal problem.  When in RCV, the grid voltage
is -170v, and when in XMT the grid voltage is -2.5v.  When the quiescent
plate current disappears in XMT, the grid voltage is still at -2.5v
indicating that the resistive divider circuit and choke are OK.  We suspect
a problem with the center tap of the filament windings of the transformer.
The transformer is a relatively new replacement from Peter Dahl.  

Has anyone ever run across this problem?  What was the cause?  What was the fix?
If ANYONE can offer any suggestions please let us know at w5asp@aol.com.


73, Joe, W5ASP

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