Re: Toroids as O/P trannies
I have succesfuly used a small Toroidal Mains transformer as an Output Transformer in a Telefunken Tape recorder, Magnetephon KL85 I think or something similar.
The original transformer had a tertiary winding for negative feedback so it wasn't straightforward to find a replacement. I think I used a 9V + 9V type (Might have been 6V + 6V) from Farnell which gave a reasonable impedance match (Impedance ratio = Voltage ratio squared). One secondary was used for the Loudspeaker and the other for Feedback. It worked fine. Sadly some months later the motor burnt out and as yet haven't got a replacement. Anyone got one??
These transformers are unlikely to work in a single ended output stage as the quiescent standing current will almost certainly saturate the core. It would be wise to make sure that both valves in a push pull stage draw similar quiescent currents as a significant difference may still saturate the core.
It should also be noted that if the primary is wound in a bifilar fashion (Both primary sections wound together side by side), the insulation may not be up to the job if the HT is too high. In my small 6W push pull stage ( 2 x EL95) it worked fine. At least it got it working again.
Denis
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