[Amps] VOX Tripping and Bandswitch Damage

[Bill Coleman]

Hi Mike, you may be on to something...   I am not familiar with the '78, but
will relate something I have personally done & seen done by other folks.

Our club has an SB-220.  The stock Tune, Load, and Bandswitch knobs are
identical.  On more than one occasion while tuning it up, the bandswitch was
cranked by mistake - under power!

The fix was easy:  a smaller, very different knob for the bandswitch.

It's really ugly, but when the operator is unfamiliar with the gear, the
contest is raging, the multiplier you need is on another band....  it's best
to minimize the potential for misteaks,  errr.... mistakes.

Good luck!   73, Bill  N2BC


----- Original Message ----- 
From: "Michael Tope" <W4EF at dellroy.com>
To: "AMPS" <amps at contesting.com>
Sent: Friday, October 24, 2003 2:47 AM
Subject: [Amps] VOX Tripping and Bandswitch Damage


> Between the two Alpha 78's that we have at the local club
> station, we have had a number of mysterious bandswitch
> failures over the last few years. As these are costly and
> or time consuming repairs to make, I have made an
> effort to get to the root cause of the problem. Unfortunately,
> given that we have a number of operators who come and
> go at the station, its been rather difficult to ascertain exactly
> when the failures occurred, let alone who was operating at
> the time, and what, if anything, they were doing wrong that
> might have caused or contributed to the failure.
>
> Recently during a discussion of this problem, a fellow
> club member suggested that perhaps it was related
> to people using VOX. He had noticed that the bandswitch
> on the Alpha 78 which makes a rather loud "clunk" when
> switched, can easily trip the VOX on our Kenwood
> TS-950SDX if the VOX function happens to be on at the
> time. This observation raises the question, is the timing of
> the bandswitch clunk and the RF rise time delay in the
> exciter sufficient to cause hot switching in this scenario
> (e.g. have the switch contacts closed by the time the RF
> envelope from the VOX event reaches them)? It seems like
> a plausible explanation, but without making measurements,
> I don't know if the timing relationships are right or not.
>
> Anyone have thoughts on this?
>
> Thanks,
>
> Mike, W4EF..................................
>
>
>
>
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