[ARC5] Brian's deaf set

[hwhall at compuserve.com]

>Those audio output transformers are failing at an increasingly rapid rate lately
 

 Has anyone pulled one apart to see how difficult it might be to rewind the originals?

Wayne
WB4OGM

 

-----Original Message-----
From: Kenneth G. Gordon <kgordon2006 at frontier.com>
To: Leslie Smith <vk2bcu at operamail.com>
Cc: ARC-5 <arc5 at mailman.qth.net>
Sent: Thu, Sep 29, 2016 6:51 pm
Subject: Re: [ARC5] Brian's deaf set

On 30 Sep 2016 at 7:23, Leslie Smith wrote:

> He's had time to think about the problem - there are a few details he
> didn't mention.
> 
> He now suspects the AF output transformer - or just as likely the SM
> capacitor across the AF o-p xfmr primary.

Those audio output transformers are failing at an increasingly rapid rate lately, and the 
voltage applied to the receivers, or the current through the transformers, appears to have 
nothing to do with that problem.

I suspect that the problem MAY be related to the same sorts of problems which effects many 
older audio, modulation and interstage transformers: use of acid-based paper between the 
windings which eventually causes corrosion of the fine wires in the primary side (mainly).

Or perhaps the very slightly acidic beeswax eventually does them in. I dunno.

I have several failed ARC-5 audio output transforners here which I have thought about 
rewinding....THOUGHT about...

There is a source of inexpensive "line-transformers" which, I believe, Jeep pointed us 
towards which will work perfectly as far as the primary side is concerned. These are 1 or 2 
watt line transformers which sell for about $4.95 each. Primary impedance of one of the 
windings  is 8 K ohms, which matches the output side of the 12A6 nearly perfectly (7500 
ohms).

There are a couple of problems (as I see it) with them: 1) the only secondary output 
impedance is 8 ohms and 2) one would have to mount them on some sort of plate which 
would have to be drilled to match the mounting holes of the original transformer in order to 
not have to drill "weird" mounting holes for it. You would have to use #3 hex nuts and 
lockwashers inside. And 3) they aren't original, and 4) won't fit inside the original AF 
transformer can either.

Ken W7EKB

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