[Milsurplus] SRR-11/12/13 etc...running hot...

[Kenneth G. Gordon]

One of the reasons I asked about these is that about 30 years ago, 
I worked for a strange psychologist who was doing VLF propagation 
research (!). He bought a number of the SRR series receivers and I 
did a lot of work on them.

I shortly discovered that the RCA engineers had all of the tubes 
running with the screens tied directly to the plate voltage source so 
that the screen voltage was only a volt or two, if that much, below 
the plate voltage. This (obviously) made the tubes run very hot.

I "adjusted" most of those receivers he used by installing 56K 
resistors in the feed to the screens, dropping the screen voltage to 
a more reasonable level in those stages I could.

Max temperature dropped WAY down, receiver noise was lowered 
and reliability of the tubes went up. Although over-all receiver gain 
and audio output level suffered a bit, for his purposes it didn't make 
any difference.

He used them to monitor VLF stations 24/7/365 and recorded their 
output levels on Rustrak recorders. Had to disable the AVC for this 
to work. I don't remember if the SRR-11, etc, had an AVC off 
switch.

Before I made the mod, I had at least two receivers ALWAYS on 
the bench. After I made this mod, I had to work on them very 
seldomly, and they were very reliable.

Ken Gordon W7EKB