Testing for grid current on sb-200

[Peter A Markavage]

With the Harbach soft key mod, this is the voltage you will see on the
relay key jack. Leave the mod in. You don't need to add an outboard relay
to key the relay in the SB-200. It's approx. 1 volt and low current so
the newer solid state rigs can easily and safely key the amplifier. I can
use my Icom 706 to key the SB-200. My TS-830 and my C. E. 100V are also
used with the SB-200. The soft key makes the SB-200 far more versatile
with a lot more transmitters and transceivers. If you feel that somehow
the soft key is part of the problem, contact Jeff, at Harbach
Electronics. I'm sure he can shed some light on this issue.
Pete

> > I get 1.077 volts dc at the amp relay jack.  This was described
> as
> > grid
> > bias also?
>
>   I have no idea what the Harbach mods are, but in a stock SB200
> you'd have about -100 volts at the relay key jack.
>  Which is also the cutoff bias voltage when the amp isn't being
> keyed.
>
> > Please tell me the safe (realtively) place to check the grid
> current
> > and
> > bias voltage.  At the base of the tube at the ground to grid pin?
> > Is
>
>   With the amp keyed but NO DRIVE you should measure about
> -2 volts or so at the junction of R21 and R22, When the amp is
> NOT keyed, you should measure about -100 volts or so, but with
> the Harbach mods, hard telling.
>
>   BE VERY VERY CAREFULL!!!!!! The 2400 vdc in the plate supply of
> this unit will kill you quickly!
>
>  Without knowing what the harbach mods are, its difficult to give
> accurate advise as to what to check, if I wre you, I'd take out
> the Harbach mods, put the amp back to stock and use a small
> 5v dip relay to key the amp. These amps worked for 25 years without
> mods and it takes nothing more than a relay to remove the high
> switching voltage from your rig.
>
>   73,  Mark  WB8JKR

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