[Milsurplus] SRR-11/12/13.

[Kenneth G. Gordon]

David Stinson wrote:

> The SRR series receivers have a big, glaring design and
> material flaw.

Well, yes, if we consider that they are well over 50 years old now.

> That would be OK, except that they cheaped-out on the
> materials for the levers.  They're made of some cheap
> pot metal and one end of the split section fractures,
> leaving that shaft stationary while the others rotate.

Yes. This is the most common problem with them. However, Josh 
Rovero has an article with diagrams and photos of a fairly easy home-
made replacement for those pot-metal cranks. I don't have the URL 
handy though.

> Next problem was the soldered-in tubes in the modular
> sections.  I guess you're supposed to replace
> the entire dud section with a spare, but that would make
> for a pretty expensive spares set.

Actually, the tubes were meant to be un-soldered and replaced if 
necessary. The tubular capacitors in the RCA/SRR receivers, however, 
are very high quality metal-ceramic types. So far, in all the SRR 
receivers I have rebuilt, I have NEVER yet found a bad one.

Lastly, the big problem with over-heating the submini tubes is caused 
by a particularly stupid (IMHO) design flaw: the screen voltages on 
nearly all of the tubes is equal to the plate voltage! I have forgotten the 
details at the moment, but it seems to me that in most of the modules, 
the screens are connected directly to the plate voltage source.

Now, I am not a receiver design engineer by any means, but I always 
thought that was really, really stupid. So, I add 56K resistors between 
the normal plate voltage connection and the screen connection of each 
tube, with bypass caps where necessary.

Overall heat drops drastically, yet receiver performance seems not be 
to effected at all, although I have NOT taken the time to do a "before" 
and "after" series of measurements to prove this.

As W.Donzelli says, when the submini tubes are treated properly, they 
are MUCH more reliable than most other tubes.

After all, they were used very successfully in proximity fuses for AA 
shells.

Ken Gordon W7EKB