Reverb transformer as OT?

knuckleberryfinn

In the words of the late Lou Reed, it's a lonely Saturday night.  So...output transformers!  Can I use a reverb transformer as an OT for a low-powered push-pull power amp?  I have a reverb transformer hanging about, and want to build something around one watt.  I know the Firefly on AX84.com uses a self-splitting 12AU7 in push-pull, but will it work with the reverb driver (which I think is single ended)?  I really dislike single ended amps (so glad I bought that Champ 12 a couple of weeks ago) so the push-pull side of things is non-negotiable.

knuckleberryfinn

Just realised - of course I can't.  But I could use two reverb transformers and then have it switchable from SE to P-P couldn't I?

ICBM

Not really. A push-pull only works properly when it's a single transformer. (Those with more theoretical knowledge might want to correct me!)

Reverb transformers definitely work perfectly as mini SE output transformers though - that's exactly what they are. The impedance of the reverb tank is right for a speaker too (8 ohms I think). ZVex uses transformers of the same spec for the Nano amp, that's where he got the idea from .

Misterg

I think ICBM is right - both 'halves' would need to be on the same core to work as push-pull (two separate transformers would work as parallel SE).

RS do a little output transformer that works well in the Firefly and similar low power P-P circuits (part 210-6475) which used to be quite cheap, but I see is now approaching the price of small Hammond transformers (but it sounds better than the 125A ).

jpfamps

You can use 2 reverb transformers in push - pull, although you will not have the hum cancelling advantage of using a dedicated transformer as the magnet field induced by the DC current draw through the OTs will not cancel as they have separate cores.

This would be an eccentric design to say the least, and I'm not sure there would be much advantage over parallel single ended.

Hammond make a range of small PP OTs that allow a wide variety of primary impedances, and would be ideal for this type of amp, eg the 125A.

You can switch between PP and SE by shorting the drive line to one side of the PP pair.

Be careful though Randall Smith and Peavey have patented this!!