[Collins] R-388 service hint

[Craig Roberts]

As you may recall, I was having some difficulty with my R-388's AGC a 
couple of weeks ago -- loss of action on strong signals, audio 
distortion and low S-meter readings.  I was convinced it was related to 
the use of JAN tubes -- in particular a 6BE6/5750 at V106 (2nd mixer).  
Civilian 6BE6 tubes seemed to work fine but military tubes appeared to 
fail after a few hours. 

Well, a few days ago my civilian 6BE6 at V106 failed, too.  Apparently, 
the fault was not in the tube(s).

Further inquiries were made on another forum and a veteran Collins tech 
wrote to reveal that he'd seen this precise problem before in certain 
R-388 production runs (mine -- Phila. 53-56 -- included).

The REAL culprit, according to this gentleman's valuable old shop 
notebook, was C136. It's a 100 uf mica -- just like the notorious C204, 
which I'd been warned about (and replaced) early on. The story goes that 
Collins acquired a bad batch of these 100 uf micas which may have had 
compromised cases and used them in two R-388 production runs.  Many of 
them failed with resulting troubles identical to mine.. So, I replaced 
C136 and my AGC has performed flawlessly since. The radio's been on 
continously for well over 48 hours now with a JAN tube installed.

So, I've learned another lesson and thought I'd pass along the hint.  
I'll be replacing the rest of the 100 uf micas in my set, too.

73,

Craig
W3CRR