Single tube guitar amp, adding a transformer to a formerly transformer-less design

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Building a small practice amp from a reclaimed phono circuit.

Formerly used a dreaded selenium :eek: for 24v, I'm planning on using a transformer laying around for the heater but wanted to know if i need to consider any other factors. Added a filter cap and a fuse to the ac in. Formerly a Motorola Suitcase Phonograph, now housed in a dead ss marshall practice amp chassis (already had a 24v trans! :D ).

Considering a pre-amp to get some more volume and gain, i know it's not gonna be loud, just looking for unique tone and a fun amp using a single cheap valve.

I can post the schematic (original and proposed amp both) if needed.
Chassis is grounded. Looks like the reason they went with this tube is it used 110 for the plate, and a 25v heater. Looks like i'll need a 2nd transformer too as in addition to the selenium hack, they also used the phono motor as a step-down.

Am I correct in my assumption I can use 2 transfromers of the same value back to back (110vac->12vdc->110dc) to get isolated line voltage for the plate?

Yes, chassis is grounded already, just sorting out what needs to fit an where. Going to try to keep all the xformers and the 25L6GT inside the cage as it's not too hot and I'm adding a ventilation grate and some internal shielding. The chassis is an old 6" driver combo amp.

Instrument amps are not my thing, but this thread has stuff of interest to me.

Start with the nnL6 data sheet and facts emerge. 1st, you will be quite OK if you bridge rectify "120" VAC to obtain the B+. 2nd, the power pentode needs several volts of drive signal.

As a 50 VA N-68X from Mouser costs $11.20, why bother with back to back filament trafos? Full wave bridge rectify the O/P of a N-68X, filter, and you've got your B+ rail. Either 4X UF4007s or 2X UF4007s and a 117Z6 (for sag) make up the bridge.

Several stages of voltage gain are needed between the guitar pickup and the power pentode. The phonograph "donor" used a crystal cartridge whose O/P was a few volts.
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Thanks Eli for the detailed info (and thanks mods for moving the post)

I was planning on basically integrating an overdrive (gain) pedal to drive the tube and put enough juice into the phono circuit.

I have since decided it was a bit more trouble than the tone would reward, and bought another tube project. I figured the transformers (of which I have many) might be easier.
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