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previous: R.G. I think you can use the EZ81 in the... -- 3/8/1998 10:04 AM

Re: Old EL84 transformers

3/9/1998 3:05 AM
stephen	Re: Old EL84 transformers I have too much respect for RG's many years' of good advice, to make a public disagreement here... but I'd be very cautious about running a tube rectifier heater off the same winding as the amp's other heaters. I once requested this from my local one-off winder (semi-retired from a lifetime making trannys) and he just refused to do it! He delivered the ordered tranny with _two_ 6.3V windings, explaining that he'd had to fix too many disasters where the heater-cathode insulation had failed in an EZ80 or EZ81 rect tube on a shared 6V heater supply. (With a separate winding, it hardly matters.) I don't know an exact 5V equivalent for an EZ81, and my US friend who builds such amps hasn't found one either. The closest in sound was two 5Y3's, but you probably wouldn't have enough space or heater current. A single 5V4 will run an EL84 p-p amp nicely. ( That's Five-VEE-Four, not a typo) Alternatively, if there's room between the windings and the window in the iron, your tranny probably runs on something like 7 turns per volt, so somewhere between 5 and 10 turns of _WELL_ insulated wire around the windings and connected in series with your existing 5V winding, would give you around 6.3 volts for an EZ81. Check voltage on load and add or take a turn or so. If you get _less_ than 5 volts, reverse the ends of the added turns. - Stephen

3/9/1998 3:05 AM

stephen

Re: Old EL84 transformers

I have too much respect for RG's many years' of good advice, to make a public disagreement here... but I'd be very cautious about running a tube rectifier heater off the same winding as the amp's other heaters. I once requested this from my local one-off winder (semi-retired from a lifetime making trannys) and he just refused to do it! He delivered the ordered tranny with _two_ 6.3V windings, explaining that he'd had to fix too many disasters where the heater-cathode insulation had failed in an EZ80 or EZ81 rect tube on a shared 6V heater supply. (With a separate winding, it hardly matters.)
I don't know an exact 5V equivalent for an EZ81, and my US friend who builds such amps hasn't found one either. The closest in sound was two 5Y3's, but you probably wouldn't have enough space or heater current. A single 5V4 will run an EL84 p-p amp nicely. ( That's Five-VEE-Four, not a typo)
Alternatively, if there's room between the windings and the window in the iron, your tranny probably runs on something like 7 turns per volt, so somewhere between 5 and 10 turns of _WELL_ insulated wire around the windings and connected in series with your existing 5V winding, would give you around 6.3 volts for an EZ81. Check voltage on load and add or take a turn or so. If you get _less_ than 5 volts, reverse the ends of the added turns.

- Stephen

Replies:

JR NO NEED TO WORRY ABOUT HEATING TH... -- 3/9/1998 5:40 PM