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

[Bob Betts]

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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