CCDA using 5670 tube into repurposed 1:3 transformer?

[capacitorless]

I'm finally starting to plan out a mic build after a ton of downtime. I've got a decent (AKG nylon CK12) LDC capsule, and a Tamura GA80017 1:3 mic transformer from a PM2000 channel strip. I would like to design around a 5670 tube. Not trying to emulate any particular mic, but I'm leaning towards a C12/251 type body/headbasket.

I'm struggling with the transformer part of the equation. If I'm using the 2nd half of the tube as a cathode follower (CCDA: constant-current-draw amplifier), would a lower ratio transformer like the Tamura at 1:3 work ok? It's a fairly substantial transformer, but there should be room in the body.

Any thoughts/opinions/flames?

 

[rock soderstrom]

In general, you shouldn't overestimate the current potential of a CF, but in practice you can build a CF tube microphone without a transformer if the cable runs are short. (this has been done successfully)

So a 3:1 transformer would improve things, some of the gain of your CCDA circuit would be swapped for current, the impedance would be reduced and the whole thing would have symmetrical signal routing. What more could you want?

Pure CF circuits also work great with low step down transformer, see Sony C37a, Dave Royer mics etc.

Here is a list with cathode follower mics...

 

[capacitorless]

It would be great to start off with a more simple mic in terms of the what's inside the body, then swap out transformers at the power supply end of things, until I get to something nice

The C37a uses a 6au6, and if I don't have a transformer in there, I should have room for two of them (wired as triodes, natch). That could be interesting!

I'm inspired by the Magmic MM-2000 that I used to have, that used an e88cc, with a plate driven transformer. No preamp required, output level pretty hot.

 

[rock soderstrom]

It would be great to start off with a more simple mic in terms of the what's inside the body, then swap out transformers at the power supply end of things, until I get to something nice

As an example, here is the Country Boy by David Royer. He uses a Jensen JT-16-A (1:2 mic input) in the PSU box, which would be very similar to your project, except that you want to use a CCDA instead of a pure CF.

The C37a uses a 6au6, and if I don't have a transformer in there, I should have room for two of them (wired as triodes, natch). That could be interesting!

Double cylinder V machine

 

[capacitorless]

Hot but probably manageable The Magmic uses some mesh over the Maglite's switch hole for ventilation, and I could do something similar.

I'm going to give this a shot. I don't know whether I would saturate the Tamura enough to cause permanent damage, but they aren't super expensive. Good learning experience.

 

[k brown]

In general, you shouldn't overestimate the current potential of a CF, but in practice you can build a CF tube microphone without a transformer if the cable runs are short. (this has been done successfully)

So a 3:1 transformer would improve things, some of the gain of your CCDA circuit would be swapped for current, the impedance would be reduced and the whole thing would have symmetrical signal routing. What more could you want?

Pure CF circuits also work great with low step down transformer, see Sony C37a, Dave Royer mics etc.

Here is a list with cathode follower mics...

In a correspondence I had with Royer, he said his CF mic projects are perfectly happy without an output transfomer, and can drive 50' of cable.