Heath GR-64 Audio Distoration Problem

[Charles Seitz]

Good work Mark.  Simple solution but not a trivial task to find it.
Doesn't that make you fell good when you can
get an old radio to work after all those years?

---  CHAS  WA2DYA


----- Original Message -----
From: "Mark V. Johnson" <mvjohn at SYMPATICO.CA>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Thursday, December 23, 2004 13 42
Subject: Heath GR-64 Audio Distoration Problem


> Heath team;
> Very snowy day here so I thought I would  share my latest repair
> adventure. A very humbling experience when you consider a GR-64 SW
> receiver is really nothing more than  a souped up "All American Five"
> radio.
>
> I go this cheap at a swap meet in the fall and grabbed it as the front
> plastic dial piece was not cracked or scratched. I have an affection for
> GR-64's as I got on as a kid at Christmas in 1969. It was my first real
> SW receiver and one of my first Heathkits
>
> This radio was very well built. In fact a sticker attached inside showed
> it belonged to a Radio TV Repair guy. I did my usual check of solder
> connections, tubes, all voltages and screw tightness and aligned it.
> From the first moment I turned it on, I was never satisfied with the
> audio. A slight, but noticeable distortion of the audio was present. No
> tweaking of alignment or tuning would cure it. Drove me nuts. At one
> point  I actually convinced myself it was working as designed and that
> was that. I then decided it was just not right and got down to trying to
> find it. I checked all the bias voltages very carefully as it seemed
> like a bias problem. I replaced all the electrolytics as I thought a 60
> hz hum may be the cause. No change. I then abandoned logic, my scope, my
> extensive collection of test gear and pulled out the manual and started
> checking the wiring.
>
> Sure enough, found it. Capacitor C24 a 500pf cap had a .005mfd cap in
> its place. From hindsight, its easy to see what happened. The builder
> likely ignored the step by step instructions and placed components on
> the circuit board by using the printed values. 500 upside down can be
> quickly read as .005. This cap is part of the AGC filter circuit.
> Changed it out (to 500 pf as per spec) and now the radio plays
> perfectly. This radio never worked right from day one!!!
>
> The lesson is that one again, we (I in this case) need to be reminded
> that Heathkits are kits and you can't assume they were built right in
> the first place. I've fixed many tough bugs over the years but this
> simple one almost got me!
>
> Best of the season everyone!
>
> Mark V. Johnson VE3DJU/VE3DDI
>
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Products bought, sold or traded here is the responsibility of the
parties involved.  This list and the City of Tempe are not responsible
for losses or misrepresentations of any kind.  Buyer beware!

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This list is a public service of the City of Tempe, Arizona
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