Class A tube amplifier using just one 12AX7

[frequencycentral]

I found this schematic:



http://www.allaboutcircuits.com/vol_6/chpt_5/19.html

I'm no expert with tubes, having used them only for Valvecaster/Subcaster, But could this schematic be adapted into a tiny low powered guitar amp?

I really don't understand output transformers and impedance matching yet! This schematic uses an automotive ignition coil as an output transformer. Is there a better way?

Any experts out there willing to rationalise this into something we can all build?

[R.G.]

It's simpler to get a Fender reverb driver transformer. These are designed to drive an 8 ohm load from a 12?7 plate, and are shielded as well as much smaller. They're relatively cheap as well.

That still leaves you the problem of making 100 to 300V and 6V or 12V for for powering this thing.

[frequencycentral]

Thanks R.G.

Ebay have this: Reverb Driver Transformer for Fender 22921 Item number: 200220005423 - I think it would cost a small fortune to ship to the U.K!

Ok - so the plate load of a 12ax7 is 15K, the transformer output is 8 ohm.

A schematic for the power supply is included on the web page: http://www.allaboutcircuits.com/vol_6/chpt_5/19.html

[frequencycentral]

This one's cheap for UK delivery: Reverb driver Transformer for Fender Tube Amplifiers  Ebay Item number: 370031587677  Primary Impedance: 25000 Ohm. Secondary Impedance: 8 Ohm
- But is the primary impedance wrong?

[ambulancevoice]

yay, a 12ax7 amp! be its only about 1 watt
could probably use a preamp

[Derringer]

here's a 2 watt push pull power amp schem from www.ax84.com

http://www.ax84.com/static/corepoweramps/2W_PP/AX84_2W_PP_Poweramp_Schematic.pdf

I've only built two amps so far, but if I were you I'd stay away from the schem you posted. There's too many variables there.

I highly recommend the ax84 group/site if you want to build something small ... or large

[frank_p]

If you build that, watch out for the high Voltages running around the transformer and the speaker.  Be sure to disconnect every power supply before fooling around the circuit (even like touching the speaker).  There is no grounding anywhere on the frame of that kind of transformer-coil.