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[Amps] al80a

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Subject: [Amps] al80a
From: Ian White, G3SEK" < (Ian White, G3SEK)
Date: Sat, 3 Aug 2002 08:53:27 +0100
Tom Rauch wrote:

>> >is no good. I should have a known good one tomorrow to check it out.
>> >In the meantime I have seen several things that need to be done.
>> >glitch diodes, glitch resistor, new suppressor unit, etc. Live and
>> >learn (or re-learn??)
>99% of that stuff is just needless folklore originated by people who
>sell kits.
While rooting around inside the SB-1000, I checked the carbon resistor 
in the paralytic choke... good as new.

>> Take care about the glitch diode. In an SB-1000 (same animal) that
>> someone else had "pre-repaired", I had weird meter readings on 160m
>> until the glitch diode was replaced with a 1N5408. It turned out that
>> his no-name diode was rectifying at 1.8MHz!
>He might not have installed the RF choke or the bypass caps, or used a 
>diode with a low threshold voltage.
The RF choke and bypass caps were there as standard. Since the screwy 
meter readings were only on one band (the lowest) I put it down to RF 
rectification rather than purely threshold voltage.

> > While you have the cover off, it's also worthwhile to fit a step-
>> relay. Rich's simple circuit is hard to beat: the relay is a 12V DC
>> type, powered from the existing +12V rail. At power-on, the step-start
>> resistor in series with the mains, so it takes a little time for that
>> rail to come up, and this generates the delay.
>AL80-A's have that in them. Heath did not choose to do that for some 
>reason. Virtually all AL80A's have the glitch diode also.
Sorry, I'd believed the SB-1000 and the AL-80A to be virtually identical 
(over here, we don't see enough of either model to compare in detail). 
Are there any other important upgrades that would be worth applying to 
the SB-1000?

Out of curiosity, has anyone tried an aluminum top cover to reduce the 
hum? The stray field from the transformer makes the steel cover act like 
a loudspeaker.

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                           'In Practice' columnist for RadCom (RSGB)

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