[HBR] Re: GB> RSGB Keyer

[Mike McCarty]

Chris Trask wrote:
>>> 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.
>> This conflicts with your statement that it's a multivibrator, which
>> requires two gain stages.
>>
> 
>     Try using the simpler term "timer", if it's easier for you to
> comprehend.

Condescension is always so unattractive, don't you think?

It isn't a matter of comprehension. I comprehend what you wrote. It's
just that what you wrote is incorrect. A multivibrator is two inverting
gain stages with the output of each connected to the input of the other.
A timer is not an MV (necessarily) nor is an MV a timer (necessarily).
Even if the first stage were a timer[*], it is not a multivibrator.

I'm all for generalizing and seeing correspondences between different
kinds of circuits for purposes of understanding their behavior in
multiple ways, but I can't quite stretch a single stage like that
into being a multivibrator.

Considering the second stage as a V/I converter is a bit of a stretch,
though a somewhat reasonable one. The plate current at zero grid voltage
(first stage here) is about 30 mA or so. That means that the first
stage is capable of saturation. If this occurs (which it will) the
cathode will have about -40V on it, coupled to the grid of the second
stage. The second stage cathode voltage is variable from about -120V to
-92V. That means that the second stage is going to be definitely
saturated. When the first stage is cut off (like key up) the grid of
the second tube is at -120V, so it will be cut off (when the "weight"
control is adjusted to midpoint, say about 110V) since the grid
will then be about 10V negative relative to the cathode.

It's a bit of a stretch to call it a V/I converter when it operates in a
digital mode.

[*] I'm trying only to address the point you make here. Exactly how
the first stage operates is a separate issue.

mike
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