Output transformer - when needs must
I have recently discovered an open circuit primarily of an output transformer built into the back of a old speaker of unknown origin that was rescued from the hoard. I’m just in the process of restoring an old cossor battery set missing speaker and transformer.
The speaker is in ok working condition and has a 2.2 ohm impedance. I’m going to be matching this to a 220HTP. The optimum load impedance for the output pentode is between 17-19Kohm depending on which tube data sheet is referenced. Which looks very high to me based on past experience?
After raiding the hoard again I find that I have a few spare output transformer but these are from more modern sets likely of the EL84 flavour with a much lower impedance ratio than I’m looking for probably 5-7kohm. I also have a new transformer from RS that may get me to 15k
Based on my experience I have found that perfect matching really isn’t necessary and wasn’t perfect even back in the day when these were built, but I still want to do the best I can.
If I want to use what I have which is really my only choice at the moment I’m thinking of either looking for a higher speaker impedance or wondered or if I can just increase the speaker impedance by adding some Additional R to the voice coil.
Just wondering if I’m likely to be walking into any traps here.
Many Thanks Regards Chris
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