Hi Jim,
I was particularly interested in this part of your response:
> In any event, the AUX contacts on it are only rated for 28 vdc !! You
> will destroy
> them, if using + 120vdc for switching cut off bias. +120 vdcv for cut
> off bias is
> dinosaur technology. Better to simply use a 100 K 3 watt MOF in the
> CT of the
> fil xfmr.. and short the same 100 k R out with the contacts of the
> bias relay.
> Only a spst relay is required for this.
I discovered the 28VDC rating of the aux contacts AFTER I bought the damned
thing... D'oh!! The rating may have more to do with total power dissipation
than with voltage above ground, so it might work anyway... I'm open to
trying your idea, though, once I understand it.
In the SB-220 (and also I think other similar GG amps from the same era),
the center-tap (C.T.) of the filament transformer is connected to the common
pole of the SPDT contacts. In RX mode, the normally-closed contact provides
the C.T. with cut-off bias (120VDC). In TX mode, the 8+V operating bias is
connected to the C.T.
Can you be more specific in your recommendation? What are you connecting
through the 100K ohm resistor to the filament transformer C.T.? The
operating bias, I would have to think -- with the resistor shorted out in TX
mode. In RX mode, then, the tube cathodes would get the same operating bias,
but through the 100K ohm resistor. I'm not quite visualizing how that would
work in cutting off the tubes. Please explain?
Thanks,
Bill W5WVO
>
> On another note. He is using 2 x vac relays + 3rd relay... with all
> their coils in series, plus
> a shunting resistor across the bias relay coil. This will work with
> +120 vdc.. and
> speed all 3 x of em up.
>
> On the 2 x GS35B 6m amp, I helped a friend with... we used 3 x
> Gigavac GH-1's
> [like a rj1a] one for input, one for output, 3rd one for the bias [
> shorts out the 100k R]
> All of em have 12 vdc coils. All are very easy to speed up with an
> overvoltage.. and just one
> series dropping resistor. If u want to speed em up even faster, install
> a 50 uf lytic across
> the dropping resistor. Then u end up with a 'RC hotshot speed up
> circuit' .
>
> On the 6m amp.. both GH-1's mounted side by side, with 2 x SO-239's above
> them.
> Bypass swr on 6m is dead flat.
>
> For his proposal, I would deep 6 the idea of using +120 vdc for cut off
> bias.. and
> use the 100k R in the CT of fil xfmr. We always use 2 x 100 K in
> parallel,,, for
> redundancy.
>
> later... Jim VE7RF
>
>
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