[Boatanchors] Failing Mica Caps.

[Carl]

----- Original Message ----- 
From: "BLIMPY" <blimpboy at sonic.net>
To: <boatanchors at mailman.qth.net>
Sent: Tuesday, October 14, 2008 5:33 PM
Subject: [Boatanchors] Failing Mica Caps.


>
> Ok fellas ! I surrender !!
> Several of you have written to say that " Yes Virginia Mica Caps Do 
> Fail ".
>
> All of you citing Collins Recievers incidentally.
>
> Ok,  you'll get no arguement from me.
> Voltage, moisture, poor manufacture, poorly spec'd devices, dirt, time 
> take thier toll on everything under the sun.
>
> Yes mica's do fail.
> No, I dont get any Collins rigs through here to work on, so I yield to 
> your specific experiences there.
>
> I do however overhaul a LOT of recievers including many Zeniths and 
> similar dating back to the mid 30's and etc.
> It is exceedingly rare to encounter a bad mica in  these radios.


A lot may be due to the enviroment that the particular Zenith lived in 
as they do fail.
Out this way all brands are suspect, I do a lot of Zeniths also in 
addition to Philco, RCA, GE, Scott, and all the rest. I specialize on 
the higher tube count radios including consoles and dont get involved 
with AA-5's and similar where lower quality components are often used.

Between recapping, resistors, rotten rubber wiring, crazy motor drive 
and selector mechanisms, silver migration in IF cans, etc  full 
restorations are not a one day affair or for the beginner.

Since I use a quality Tek scope to monitor the signal path along with 
various pieces of HP gear, I may find a few more problems than the 
average repairman using 50-60's TV shop test equipment.



  The radios
> I do commerically are guaranteed for 3 years..
> the longest such guarantee in the USA.  I have been waiting over 23 
> years for the first radio to come back.
> Your milage may vary.


I still receive letters from people who have a 30's-40's radio I rebuilt 
in the 60's and 70's as I include a small label with my name, call and 
date under the cover. There is no reason that when done right a restored 
radio lasts for decades with minimal attention. Its often very 
interesting to read the stories of the radios subsequent owners over the 
past 40 or so years.


>
> Same deal with  the 50's-60's and later vintage transmitters and most 
> recievers mere mortals can afford.
> In these, about the dumbest thing you can do is start messing around 
> in the VFO futsing with micas, npo's and etc.


Post WW2 electronics are starting to show more and more mica problems. 
Hammarlunds as already mentioned, from Super Pros and into the 70's.

Hallicrafters and Nationals are not immune either.

Anyone who has R-390A experience has been the mica route in the IF 
module and its far from just a Collins problem.

Ive read reports of many mica problems in WW2 radios from the basic 
ARC-5 and up.

Excessive drift or alignment problems in 50-60's oscillators can be 
traced to mica or TC dogbone ceramic caps. Sometimes it takes a lot of 
time and effort to fix since many of the TC ratings are no longer 
available or were custom when new.

The problem is going to get worse as all these items age and repair 
people arent prepared for a "never goes bad" mica cap.

Carl
KM1H
National Radio 1963-69