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

[Ian Wilson]

I wonder whether the 6AG6 was intended for use in Class B -
perhaps that explains the high current/gm at low grid bias?

Will look at a few Handbooks tomorrow. I have never looked
at the modulator circuits in much detail.

Sibley says the 6AG6 is a scaled-up 6V6. It is an EL33
equivalent. Introduced in 1938 (so no point looking for circuits
earlier than that <g>).

73, ian K3IMW


On Thu, Sep 17, 2015 at 7:33 PM, Leslie Smith <vk2bcu at operamail.com> wrote:

> 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
>
> --
> http://www.fastmail.com - Does exactly what it says on the tin
>
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>