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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Using SE transformers in a PP circuit

I’ve scavanged a number of old valve stereograms from the side of the road, these inevitably use a single ended amp. I want to convert one to a p-p amp (for guitar).

Is there a way I can use the existing op transformers (which have no centre tap)? I was thinking of using one for each anode circuit, but this site http://ozvalveamps.elands.com/optrans.htm says “You can't, for example, use one transformer in each anode circuit because both will saturate on unbalanced DC.”

I there any way around this? and can anyone give more detail on how this happens?

Pete McK


2007-04-24 10:55 pm
You will probably not saturate the opt's since they are designed for SE and as such they will manage the DC current they were designed for.
So it really could work as long as you stay in pure class A howerver the coupling between the two primarys will not be that great if you venture into AB territory.

Thanks for the responses guys.

Perhaps this will help?: ‘reassemble the transformer laminations with all the Es inserted into the former from the same side with the Is clamped across the open side’

Re:'the coupling between the two primarys will not be that great if you venture into AB territory' - what problems would this cause?


2007-08-08 12:12 am
restacking all the Es on one side and the Is on the other creates what is called a "gap". This gap prevents the core from saturating when used as a single ended transformer. Since your transformers are already single ended, they most likely have this gap (If they're open faced in a little metal bracket the gap is under the top of the bracket - generally, and glued). Have you considered a stereo guitar amp? It may be very interesting sounding with a pan pedal or something-perhaps a reverb only channel on one speaker and a clean only on the other? For a P-P guitar amp transformer I would almost recommend trying to use a power transformer with the right impedance ratio...it'll sound grungy, but it'll be cheap...or check out weber, edcor etc. many P-P xfrmrs for 5-25w for around $15-30.