[Premium-Rx] Watkins Johnson 8711A Repairs after 10 Years

Tue Jul 30 18:10:23 EDT 2013

Dear Bob and the others,

You can go back an awful long way and find plenty of ancient radio still 
working and likely to do so for the foreseeable future - vastly longer than 
any design life thay may have had.  This is because most of it was very 
solidly made, there is a solid core of enthusiasts prepared to keep their 
treasures working and also because there seems to be a huge stock of valves 
("tubes" to most of you!!) available and the small components are reasonably 
plentiful.  My RA17s and AR88D march on as well as my Racal RA3701 and not 
so new RA1772.

I cannot imagine many owners of tubed Collins or Racal gear are looking for 
the garbage collection man!!

Here in the UK Yahoo groups such the WS19 group have international user and 
technical support and on-line access to an impressive library of old 
military technical manuals and user instructions.   The recent release by 
our MOD of their holdings of Clansman tactical HF and VHF gear (early 1980 
vintage) at pretty reasonable prices has increased the interest since this 
kit is compact, portable and extremely well built to MILSPEC standards.

Of course no one would pretend that their stuff can compare with the latest 
direct sampling offerings from DRM or R&S, but (and I hope no one will take 
this badly) some people feel that ancient radio is more fun to operate than 
a faceless black box.   The problem, however, is not the radios but the 
fewer and fewer AM stations to listen to as more commercials migrate to 
satellite and / or on-line distribution.  To that I fear there is no answer.

73s
Michael
G8MOB

----- Original Message ----- 
From: "Bob Betts" <rwbetts at sbcglobal.net>
To: <premium-rx at mailman.qth.net>
Sent: Tuesday, July 30, 2013 7:25 PM
Subject: Re: [Premium-Rx] Watkins Johnson 8711A Repairs after 10 Years

Gary, Steve and All:
I read with great interest (and full agreement) Steve's synopsis of the 
8711/HF1000 series receivers. This comes at a time when, by coincidence, I 
have just had a client revise a PO from a pair of refurb 8711 radios to a 
pair of new Tentec 340 units. There were several reasons for that, but 
Steve's descriptions correspond with my opinions and now the customer's 
beliefs as well. Repair parts availability, repair costs and reliability due 
to end-of-term MTBF are all serious concerns. I am by no means a very 
qualified 8711/1000 service guy. We have turned away several repairs for our 
lack of knowledge of them. However, I have kept many 8716/8718 and 86xx 
receivers in operation, but the firmware/DSP types exceed our confidence 
capabilities.

As we know, a lot of the older pre-8711 gear is still in daily use and 
apparently quite healthy. I say 'healthy' because I personally know of many 
users who have few complaints...so the averages are still with us on that 
score, but who knows for how long.

Most of our repair work has been with Racal, some Harris, Collins and 
ITT-McKay gear and some with the pre-DSP W-J stuff. My personal stash of W-J 
gear does require what I call 'occasional routine maintenance' of cleaning 
and re-springing mother board connectors, cable interconnects, tantalum 
failures and other minor issues. We never were a player in the repair 
business of this kind of equipment, but have ventured in on occasion. Our 
business has mostly been customer specific modifications, usually of a very 
minor degree. And our consulting business was mostly based on system design, 
installation and training - we'd leave most repairs to qualified guys. I 
confess that we didn't know about PCS until a year or so ago, but should 
become good pals in the near future. Much of our work was done by Geoff 
Greer ... a great guy that I will always miss.

So, I've really drifted off-topic, but I guess my point is to suggest that 
this isn't a dark day for those of us who love our older generation 8718 and 
8615 receivers. Heck, I still have (and love) my DMS-105A demodulators, 
which I'm sure are way past their expected service life. But I do concur 
with Steve on the newer generation of stuff that obviously was designed to 
meet some contractual bid-spec and not the usual agency "iron" gear like my 
390A. I still find it strange that many of the Collins 390(A) radios that I 
trained on in the Signal Corps back in 1965 are still in daily use by some 
of my associates. Let's hope that our 1980's W-J gear shares some of those 
good genes.

Gud sigs to all,

Bob, N1KPR
AmComm

http://www.bobsamerica.com
http://www.youtube.com/n1kpr

________________________________
From: Gary Geissinger <ggeissinger at digitalglobe.com>
To: "premium-rx at mailman.qth.net" <premium-rx at mailman.qth.net>
Sent: Tuesday, July 30, 2013 11:16 AM
Subject: Re: [Premium-Rx] Watkins Johnson 8711A Repairs after 10 Years

Gentlemen,

I own an 8615D, HF-1000 and other WJ gear. After this discussion I have my 
fingers, toes, and eyes are crossed hoping none need serious repair. I love 
my WJ gear. It has incredible capability.

And, since I work in aerospace and design electronics for spacecraft, I 
certainly understand design life, component derating, MTBF, and MTTR.

But all this starts to unravel for me when I think about this. I have a 
collection of electronic countermeasures gear from WW2, Korean, and the 
early cold war. It all functions. And keeps functioning. I can buy 
replacement electrical parts. I have full schematics, wiring diagrams, and 
alignment procedures. All this gear was designed and built to support a 
lifetime of about 5 years. Yet it works and keeps on working. Even my old 
beat up R-390A receivers, ART-13, and T-368 transmitters still function as 
designed in spite of multiple owners and rather rough treatment.

So while I understand the issues with the operation of units well past their 
design life, I am not convinced that it had to be like this. I just got off 
the phone with an applications engineer for a major capacitor firm. His 
"hi-rel" aluminum can electrolytic smoothing capacitors, when derated 
according to their specifications, have an 8,000 hour operational life. 
Well, in the piece of GSE I am designing, I am applying MIL-HDBK-217 style 
derating on top of their specifications ... and then some. Published data 
indicate this will give at least a factor of two increase in life. Then of 
course inrush current limiting and fault protection will help stretch the 
capacitor life as well. All this is adding about $10 to the design. Using 
stacked mono-ceramic capacitors would have added $100 or so but would have 
almost eliminated smoothing capacitor life issues. Adding conformal coat to 
the boards will improve the life as well for almost no cost.

Although it may have added a bucks to the cost, and made the units weight 
1/2 pound more, I wish WJ had been a little more conservative in production 
and mechanical design. But you certainly can't fault the electrical 
performance for their day.

Gary WA0SPM, also member US Army MARS

Gary A. Geissinger
Chief Electrical Engineer, Sr. Director, Technical Fellow
DigitalGlobe Incorporated

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