[Milsurplus] thoughts on the SRR family of radios - kinda long.

Mon May 9 23:17:02 EDT 2016

Ken said:I then experimented with one receiver, an SRR-11, by modifying every module to include a 
properly bypassed 56K ohm dropping resistor in the screen voltage feed. The result was 
that the heat produced dropped dramatically, and we no longer had heat-related failures.

I don't know what to make of this.  If I understand the theory correctly, plate current is independent of plate voltage in a pentode.  That is why the plate curves have such a flat top.  Changing the G2 resistor to a higher value will lower the Screen Grid voltage and as a result will reduce the plate current for that tube.  Yes, doing so will reduce plate dissipation but it should also adversely affect stage gain and noise as well.  Perhaps not all that noticeable by ear but I am pretty sure things will start going down hill from there as other stages are so modified.
These radios were, for the most part, built before all of the component reliability specs were re-written in the mid to late 1950's.  Those specs were changed in part because of the poor reliability of the avionics used in the B-47, the first jet bomber, among other complex weapons systems.  It made little sense to send a squadron of B-47's to the USSR if the critical systems like the Bombing and Navigation System had an 8 hour MTTF; much shorter then the flight time of the mission!  So any electronics built before the late 1950's is suspect of using capacitors prone to failure a few years after manufacture.  
I personally would suspect a leaky coupling capacitor was at fault before changing the bias on a pentode stage.  Even the highly regarded R-390A's have those pesky black beauty of death capacitors!  Then there is that hidden Tantalum capacitor in the R-390A audio amplifier module that is leaking, corroding and looking nasty.
Two other comments:The SRR-13A contains two mechanical filters, making it possible the third military receiver to use these filters.  AFAIK, the ARC-21 (circa 1952) is first, follower by the R-390A (circa 1955), third SRR-13A (circa 1957).
The photo of the front of the SRR-13 receiver in that ER article from 1991 is reversed.  I knew it looked funny!Jim

      From: Kenneth G. Gordon <kgordon2006 at frontier.com>
 To: Nick England <navy.radio at gmail.com>; Military Surplus Mail List <milsurplus at mailman.qth.net> 
 Sent: Monday, May 9, 2016 11:53 AM
 Subject: Re: [Milsurplus] thoughts on the SRR family of radios - kinda long.

On 9 May 2016 at 11:24, Nick England wrote:

> I like them fine too Ray, but your timing is off. These receivers were primarily replacements for 
> the pre-war RBA/RBB/RBC and RAL/RAK receivers, and pre-dated the R-390A. They were 
> replaced shipboard by R-390A + CV-591 for FSK/SSB (and later by R-1051).
> They were part of the Navy's big change in maintenance philosophy from component 
> replacement to modular replacement that happened post-war.
> 
> The series included the following -
> AN/SRR-11, -12, -13 shipboard LF, MF (rare), HF
> AN/FRR-21, -22, -23 shore station LF, MF (rare), HF
> AN/MRR-1, -2, -3 mobile in a waterproof case and 24v p/s option LF, MF, HF, (all very rare)
> AN/FRR-32 dual diversity HF with two R-618/FRR-32 receivers (modified FRR-23 I think)
> AN/FRR-18, -19 shore station 4 channel xtal control (or tunable) LF, HF (very rare)
> 
> Nick England K4NYW
> www.navy-radio.com

Thank you for the accurate historical and type information, Nick.

Some time ago, I was "gifted" with about 5 tons (yes, tons) of radio equipment by an old 
employer (1970s), all military surpus, mostly receivers and some test equipment. I had to 
sell off all the better stuff since at that time our growing family needed the money.

Amongst the pile were quite a number of the SRR family of receivers. I sold the NIB 
FRR-23, and an almost new SRR-13, but have had to keep all the rest since all of those 
needed some maintenance to put them back in decent operation.

I have one SRR-12, a few SRR-13/13A, and a larger number of SRR-11 models since the 
fellow I was working with was doing experimentation at VLF, recording the signal levels of 
all the Navy and some foreign VLF transmitters at his location in Missoula, Montana, 
correlating those signal levels with sunspots.

There is a phenomenon called SES for Sudden Enhancement of Signals at VLF in which the 
appearance of a "new" sunspot or CME will, shortly, be followed by a very sudden rise in the 
received signal levels of a VLF station, followed by an exponential fall off to normal levels.

Anyway, he first began using RAK receivers for this purpose, since those exhibited this very 
noticable signal rise directly at the audio output far easier than receivers which had AGC. 
After some time, he then began using more modern receivers, including the SRR series, 
and had to modify his recording methods to use the AGC voltage as an indicator instead of 
audio output levels.

At the time, I was his electronics support (he was a psychologist), and when he tried to use 
the SRR-11s running 24/7/365, he began to suffer repeated failures of one component or 
another due to the extreme build-up of heat in the enclosed cabinets.

After studying the schematics for a while, I soon discovered that the screen voltages of all 
the tetrodes and pentodes in the receiver were exactly the same as the plate voltages. 

Although according to the tube manuals, this was a normal way of using the tubes, I felt that 
this factor was allowing the tubes to be run, constantly, at their maximum rated plate 
dissipation rating. 

I then experimented with one receiver, an SRR-11, by modifying every module to include a 
properly bypassed 56K ohm dropping resistor in the screen voltage feed. The result was 
that the heat produced dropped dramatically, and we no longer had heat-related failures.

Furthermore, I was not able to detect any reduction in the performance of the receiver.

My employer then insisted that I do the same thing to all his other SRR-series receivers, 
which I did.

I have used an SRR-13A here for some time a few years ago, and was actually fairly 
impressed with the way it worked. It was quiet, sensitive, and the dial accuracy was quite 
good.

I was also very impressed with the subminiature tubes used in them. If those tubes are 
operated conservatively, they will, literally, last forever. 

However, they are what I would term being "abused" in many pieces of equipment which 
used them, especially some of the military equipment. I have heard from ex-military folks 
that with some of the military gear which used certain of those tubes that the tubes were 
extremely unreliable in that service, yet the subminis were originally designed for use in 
proximity fuses, and some were rated for 10,000 hours of life in normal use.

As soon as I get my shop back in condition, I want to restore a good SRR-11, the single 
SRR-12 I own, and an SRR-13A and put them in operation.

Ken W7EKB
______________________________________________________________
Milsurplus mailing list
Home: http://mailman.qth.net/mailman/listinfo/milsurplus
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Milsurplus at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/milsurplus/attachments/20160510/d9d94bc0/attachment-0001.html>