3A5 tubes for cathode follower

[Dr. Toobz]

I had an idea; somebody tell me if it might be worth playing around with. The Quickie uses 7-pin mini sockets and triode-wired 3S4 mini beam-power tubes. What about re-wiring it to use another battery tube, the dual-triode 3A5? One half could be used for amplification, and the other half as a cathode follower (or both for a mu follower/SRPP), per channel. Might be interesting, esp. with long(er) cables....not sure about how it would sound.

Of course, these aren't 12AU7's - how would the low mu, highish Rp, and low current handling capacity affect such a circuit? Is this type of arrangement not possible with battery tubes?

[vanofmonks]

In the 3a5 the cathodes are tied together.  So, you can either run only one side, run them as a differential pair, or run both in parallel.  Plus the voltages will probably be too low to be useful in the quickie.

[Dr. Toobz]

Yeah, I ended up noticing that once I read little deeper. Of course, how else would you stuff two triodes into a seven-pin arrangement? I'm not a fan of paralleled tubes - I've played around on a breadboard with various triodes that way and don't like the sound. Becomes less clear or something. Guess the 3S4 is really the only way to go here, or maybe a sharp-cutoff pentode like the 1T4.

Actually, the coolest Quickie would be one using the old thoriated globe triodes, which ran on dry cells - like the UV201A. Those things light up a room! How to get 5V .25A supplies to the filaments might be a bit of challenge.....

[Paul Joppa]

...
Actually, the coolest Quickie would be one using the old thoriated globe triodes, which ran on dry cells - like the UV201A. Those things light up a room! How to get 5V .25A supplies to the filaments might be a bit of challenge.....

The way to go here is a type 31 or 71A - that can get the plate impedance down to a more acceptable value so it can drive more than a few inches of cable capacitance. The 31 can use a SLA D-cell (don't know how you'd charge it but there must be a way), while the 71A was originally used with a 6-v lead acid battery, with a rheostat and meter to adjust the filament voltage. You could probably use a 6-v lantern battery. That's getting complicated, but it's probably the better tube.  :^)