With the negative floating, RF could enter directly into the voltage
regulator IC. After receiving the email from Astron, I removed the
insulators from the negative post and cleaned enough of the paint from
around the hole to ensure good contact between the post and the chassis.
Never had any trouble thereafter.
Good luck. If you ever have problems or know anyone who does, just pass the
word. They can do with it as they will.
73, Mike N4NT
----- Original Message -----
From: "Stuart Rohre" <rohre@arlut.utexas.edu>
To: <tentec@contesting.com>
Sent: Thursday, September 22, 2011 7:51 PM
Subject: Re: [TenTec] Model 963 questions
> Astron does have some funny circuits.
>
> I think it is the 35 amp supply that uses half of a bridge for a full
> wave rectifier, instead of a bridge. In some other models maybe they do
> use a bridge as a bridge.
>
> The RF sensitivity has not been observed on a couple of 35 Amp Astrons
> at Red Cross here. These are on HF and VHF rigs.
>
> Likely the mod that fixes things is a 0.01mf disk ceramic cap across the
> DC leads just inside the output terminal bolts.
>
> The other point that should have a cap is the 3 terminal regulator.
> Look up data sheet sample circuits for the LM 317.
>
> Some have reported the outer case joints not making good electrical
> contact, and removal of paint where they overlap helps.
>
> Tightening all bolt connections especially; if the supply is moved
> around for Field Day, or portable uses, is a good thing to do from time
> to time.
>
> Stuart Rohre
> K5KVH
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