[ARC5] More on the Pullen Mixer circuit

[Kenneth G. Gordon]

On 3 Jan 2017 at 15:02, Ian Wilson wrote:

> Nice collection of the pertinent data, Ken. 

Thsnks, Ian.
 
> Just for completeness, note that (2) is only correct if you are using two
> triodes of the same type. In this case, it is necessary to set the operating
> conditions so that the triodes have different gm. The Pullen article describes
> this in some detail.

Yes. Correct. That is why Keats suggested a dual-triode tube. I am following his lead on 
this.

> If you are using triodes with different gm, then the plate voltages are whatever
> the device characteristics say.

Except that the second, mixer, triode MUST have much lower transconductance than the 
cathode-follower triode....as I understand it.

> I have had good luck with using a Pullen as a product detector,

Yes. In another 73 Magazine article, that was done. After all, a product detector is simply a 
mixer with its output at AF.

> with one
> low-gm triode and one high-gm triode from a triple-triode Compactron. I forget
> which tube that is (probably 6U10), but I seem to recall that the triodes are similar
> to (one half of) a 12AU7 and (one half of) a 12AX7. The low plate current of the
> high-mu/low-gm triode lets you use a very large plate resistor, which gets you
> lots of conversion (voltage) gain.

Kewel. Also Keats mentioned that.

Later,

Ken W7EKB

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