[ARC5] Request for info - modulator cct using 6AG6 in class "B".

[Leslie Smith]

G'day list readers!

I have been given a modulator.  100% homebrew.  I intend to use it in
conjunction with the ARC5 transmitters.  (I don't have an MD-7 etc, and
figure I have little chance of getting one.  My luck is obvious.)

I wish to find a circuit for this "thing" - although tracing is quite
possible.  Tubes used (from the 'back' end) are 6AG6G, (x2, in push
pull) driven by a phase splitting transformer.  

Driving the phase-splitting xfmr - a 6J5.  Before that a 9-pin (noval)
twin triode.  Almost certainly 12AX7 - but maybe another member from
that family.  There is an unmarked 7 pin pentode - that's clear from the
standard pin connections.  At the moment I have no idea about the
function of the pentode - I don't see the need for that much gain.

If any-one can point me to the circuit of the modulator, I'll be
pleased.  The 6AG6G is an uncommon beast.  It's a beam tetrode, base
connection similar to the 6V6, 6L6, 6F6 family - but differs in some
respects.  I'm surprised by the combination of high heater current -
1.2A- but lower bias voltage -6V, (but only spec's at 250V B+).  The 6L6
family specs are shown for higher working voltages.  This makes me
suspect that the 6AG6 is acutally capable of more than the spec sheet I
have (for the 6AG6).


       Characteristic      6V6  6L6  6F6  6AG6G
       Filament Voltage    all 6.3
                current    0.45 0.9  0.7A 1.2A
       Plate dissipation   12   20   12   10 Watts
               Bias (G1)   -12 -20  -26   -6 volts

Looking at the size of the modulation transformer I'd guess at 12 to 20
watts - understand my 'guess' lacks experience.

To re-state:  I'd like to use this modulator.  It was 'rescued' from a
sad fate from a SK's gear; it's neatly built and I'd like to keep this
working both because it's useful to me - but also because this has been
nicely built, and I'd like to keep this working for that reason.  Can
anyone point me to a circuit/article.




  73 de Les Smith
  vk2bcu at operamail.com

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