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

Tue Aug 2 12:58:02 EDT 2016

KenMy test was only for 6 hours with a modified power supply using the FRR-23 as a test bed.  With 60 VA ac power input, the temperature reached and stabilized at 107 degrees internally and the top of the case was just barely warm.  I can imagine that a rack of stacked receivers with unmodified power supplies with about 100 VA ac power input would be a bit different.
I have made two sets of brackets so that the FRR-23 and the working SRR-13A can be rack mounted.  This makes working on rhe receivers much easier than struggling with a receiver that is table mounted.  One interesting problem that popped up with the SRR-13A is that when in the case and rack mounted, it started tripping the shop GFCI.  
My work area is in the basement with a thin interlocking vinyl floor covering over a concrete floor so I had installed one GFCI to protect all plugs in the shop area.  So the last time I had this popping of the GFCI issue when working on the FRR-23, the power cord was not wired correctly and both fuses in the power supply blew.  This time fuses were still good.  
Since the GFCI only trips when the SRR-13A power switch is turned ON, perhaps there is an issue with leakage in the power supply?  But the receiver operates correctly on the bench with a direct connection for ac power to the rear connector.  Anyway, using a constant voltage ferroresonant isolation transformer cured the problem.  Now I have to investigate why there is a difference between the SRR-13A and the  FRR-23 which does not have this particular issue.  Always something to look into!
I did notice that the back apron of the SRR-13A has one less BNC connector then the FRR-23.  This extra BNC connector allows the FRR-23 to have a remote First Oscillator.  I guess this is for the diversity setup that allows the LO of one of the FRR-23 receivers to be slaved to the other.  While the SRR-13A is also capable of diversity reception, each must evidently use independent local oscillators.
More to come after I do some housekeeping in the shop!Jim

      From: Kenneth G. Gordon <kgordon2006 at frontier.com>
 To: antqradio at sbcglobal.net 
Cc: Milsurplus at mailman.qth.net
 Sent: Tuesday, August 2, 2016 10:20 AM
 Subject: Re: [Milsurplus] [RCA] SRR-13 Article, more

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

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