[HBR] Re: GB> RSGB Keyer

[Chris Trask]

>
> I can't comment on a schematic I don't have. However, adding
> a resistor there simply reduces the net Thevenin effective
> resistance of the pot. This oscillator is really hard to
> characterize, as I mentioned. It's partly a Hartley like
> circuit (similar to TNT), partly a tickler feedback, and
> partly a relaxation oscillator. The plate pot modifies
> the relaxation part of the circuitry, as does the speed pot.
> Anyway, it's worth trying. A 'scope would go a very long
> way in troubleshooting this circuit.
>

    It's not an oscillator.  It's a one-shot multivibrator with the key as
the input.  The ratio pot determines the two rates at which the 0.22uF
timing capacitor charges, and the speed pot/resistor determines the
discharge time.  The inductance of the transformer increases the dwell time,
and that may be where Ed is having his trouble.

    The second triode is just a voltage-to-current converter, with the
weight potetiometer setting the point at which the relay drops in and out.

Chris

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