[Milsurplus] [RCA] SRR-13 Article, more

[Kenneth G. Gordon]

On 2 Aug 2016 at 1:32, antqradio at sbcglobal.net wrote:

> Hi Ken

Hi, Jim.

> What serious design issues are you referring to?

I probably should have not used the word "serious": more like "annoying", but remember, I 
am working from an almost 46 year old memory. Due to too many "family" issues, I have not 
been able to work on my receivers at all for some time now.

>  I know from previous 
> exchanges you feel that the receiver gets quite hot.

No, "feel" about it: when we used them in 24/7 service, mounted one above another in racks, 
the cabinets got hot enough so you wouldn't want to keep your hand on them very long. And 
they failed regularly, so much so that I got exasperated at having to repeatedly fix them.

I cannot now remember the exact failure mechanisms, but I do know that after I reduced the 
plate dissipations of as many of the tubes as possible to what I considered to be more 
reasonable levels, both the heat, and the failures dropped dramatically.

>  I wish I could verify this but 
> even without solid-stating the rectifiers, the SRR-13 only consumes 100 VA and 
> with replacing the 6X4's with silicon, the input power drops to 60 VA.

Yes, but even 60 VA in a completely enclosed space will, IMHO, result in heat build-up.

BTW, I hadn't thought of your idea of reducing the voltage by a choice of a lower tap on the 
power transformer. Thank you for that. Back in the 1970s, I set the taps as close to the 
measured line-voltage instead.

Also, from work I did on another rig, painting the insides of the cabinets with flat-black paint 
can also reduce the interior heat by a substantial amount. In the first case I investigated using 
this method, heat was reduced by 17%, which is substantial. Some of my cases were already 
flat black from the factory, but not all were.

As I say, I do not remember the failure mechanisms, but they most certainly did exist. I also 
know, from talking with Navy ROs who used the receivers, they complained to me of 
constant failures with them, although, as I remember it, those ROs never detailed the 
failures.

I do remember complaints about "those damned sub-mini tubes", which following my own 
research on them, I came to the conclusion that the sub-minis SHOULD have been far 
MORE reliable than the 7 and 9 pin equivalients. After all, the subminis were first designed to 
be shot out of guns, and according to Sylvania's data on them, should have a 10,000 hour 
MBTF, minimum. Some were even rated at 50,000 hour MTBF.

My conclusion at the time was that the tubes must have been operated above their ratings in 
some way.

>  I have 
> measured the internal temperature after about six hours of operation and it was 
> holding steady at just under 110 degrees F in a room with a temperature of 
> about 86 degrees.  Not really hot enough to cook eggs!

Yes. I accept that, gladly, but I still insist that in OUR operation, they got too hot.

> The FRR-23 did have an open transformer in the RF module.  I was able to 
> replace it with a similar transformer from an SRR-13 module.  The replacement 
> transformer required a little filing to allow it to have the needed terminal 
> orientation.  Other then this, the FRR-23 was operational and responded well to 
> the tuning procedure in the manual.

Good. I had one FRR-23, essentially, NIB, still having the original tools mounted in it, which I 
sold on eBay some time ago. It was an excellent receiver, and the buyer is still using it as far 
as I know. He was quite happy with it.

> Perhaps you are on to something saying that the coils and transformers in the 
> SRR-13 were harmed by the salt in the air.  I have several SRR-13 front end 
> modules that have dead coils.  I cannot see how you are able to open them up 
> and then rewind them.

Those coils are all encased in what I think is a tube of some ferrite material, which must be 
broken in order to reach the coils. I have no idea how to re-encase them. I do remember 
reading from somewhere on the net, that others have had the same issues, but that although 
the ferrite "cover" cannot be replaced, the effect of leaving it is off is minimal. I also know 
from my reading that failure of those coils was a common occurrence.

>  If you want, I can send a sample of dead coil modules for 
> you to experiment with.  All I ask is for you to refund the postage.

I have loads of spare modules, Jim. Several of the receivers I got in the estate had already 
been used as a parts-source to repair others, but thank you very much for the kind offer.

BTW, I REALLY like working on these receivers: they are so well laid-out and accessible, and 
the modules are very easy to work on. I have not found the manuals to be all that bad either. I 
also find the receivers to be mechanically interesting and unique.

> If you need crank arms and such, let me know as I have a few spare to my 
> needs from the receivers I have already scrapped.

The crank-arms ARE a problem, but I also have two engineering drawings from Josh 
Rovero's site which shows how to make much more robust ones from common materials. 
Those can be made by hand fairly easily, although it is a bit tedious. The result is far better 
than the originals.

If you want copies of those drawings, let me know. I'll be most happy to share them with you, 
or with anyone else who might need them.

Later,

Ken W7EKB