[1000mp] Linear Amplifier TL922A

Thu, 28 Feb 2002 20:49:30 -0500

Another failure mode that can be more common on a rig used by a large
group of people, as in a ham club ... Something I did to my SB220 once
(shudder) ...
accidentally turning the band switch while the amplifier is under
drive. This happened right after I got it and probably related to
unfamiliarity.

In my case I turned my head away, while tuning, and started to
"adjust" the Load setting, which turned out to be the band switch. NOT
good.

I have heard of other equally ridiculous accidents on amplifiers.

Would not happen on the AL-1200 because you have to use serious,
intended pressure to turn the band switch knob. Just another reason
the AL-1200 is an excellent club station amp.

----- Original Message -----
From: "Tom Rauch" <[email protected]>
To: <[email protected]>
Sent: Thursday, February 28, 2002 7:08 PM
Subject: Re: [1000mp] Linear Amplifier TL922A

> Can't but agree on the TL922 bandswitch problems--we have one at the
> Historical Amateur Radio Club station (W3GR) and the switch contact
is
> nearly completely burned out on ten.  Hard to replace yourself, and
> expensive to have done.

Virtually all TL922 switch failures can be traced to one of three
problems.... either relay timing in the relay contacts, momentary
loss of proper load, or improper tuning.

Of course the failures all center around the bandswitch being the
lowest voltage breakdown component in the tank. What you really
want is something large that can take a momentary arc being the
weakest part, not something as fragile as a switch contact.

(I'd add an intentional spark-gap from the tuning cap stator lug to
ground, perhaps something like heavy #8 wire or a thick metal
bracket. Set the gap so it is as close as possible without arcing in
normal operation.)
73, Tom W8JI
[email protected]
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