Hi Bill
IMHO the best way to control bias/cathode current
is by means of solid-state switching. It will be
faster than either I/O relay operating at <2ms
make and <1ms break. The bias (on/off)control
transistor operates saturated so a little goes a
long way dissipation wise. I use the same control
buss for I/O relay control and bias switch.
Paul
Paul Hewitt
WD7S PRODUCTIONS
QRO HOMEBREW COMPONENTS
http://wd7s.home.att.net
>
> On Wed, 08 Aug 2001 14:37:01 -0400,
> Pete Smith wrote:
>
> >Well, I don't know, but when the T/R
> relay on my SB-220 began to stick in
> >the "on" position, it turned out to be
> the bias contacts that were the
> >worst burnt. Maybe a sign that they
> were trying to open too soon?
>
> ________________________________________
> _________________
>
> The contacts must be opening more than
> just bias, most likely the actual
> cathode current. Since this is DC, you
> should be able to suppress the
> arc by placing a cap and resistor in
> series across the contacts. The
> best value has to be determined
> empirically. I'd try a .1 uf in series
> with 100 ohms and then tweak the values
> for minimum visible spark at the
> relay contacts. You should be able to
> get the spark down to barely
> visible.
>
> This will delay the turn-off time of
> the tube by a small amount; perhaps
> a few milliseconds. Keep this in mind
> in relation to the timing of the
> other relays.
>
> Bill, W7TI
>
>
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