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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 13th Dec 2019, 12:26 pm   #21
whiskas
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Default Re: Running EZ81 heaters at 5V?

I think +/- 10% is OK for heater voltages in most cases, just don't expect ideal performance or lifespan.
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...where on earth did that spring/screw go??
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Old 13th Dec 2019, 3:15 pm   #22
ITAM805
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Default Re: Running EZ81 heaters at 5V?

Thanks again for the replies guys.

To reiterate, the tx I'm now planning to get has a single 6.3V 3A winding, no 5V as per the original post, that's gone. I could of course fit a bridge rectifier and bypass the EZ81 altogether but the owner want to keep it, so it's a case of finding something that not too expensive and ideally fits the chassis cut-out, which is easier said than done
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Old 13th Dec 2019, 4:20 pm   #23
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Default Re: Running EZ81 heaters at 5V?

It's for a small amplifier, so guessing guitar amplifier. That so called 'valve sound' that everyone raves about is generally thought to be caused by rectifier (HT) sag, so slightly under running the rectifier heater should make the amplifier sound absolutely fantastic. If the word gets out about this then everyone will be wanting to have their mains transformers rewound with a lower voltage rectifier heater winding for that proper guitar amplifier valve sound.

I don't blame the owner of the amplifier for not wanting a solid state rectifier, as it would absolutely ruin the amplifier and its characteristic sound.
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Old 13th Dec 2019, 4:34 pm   #24
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Default Re: Running EZ81 heaters at 5V?

Just to add to the above - when I did this, the valve was a U150, so basically an EZ40.

It's difficult when the repair is for someone else, particularly if they want it done on the cheap.

If that were my amplifier, then I'd want to try the lower rectifier heater voltage and get thrashing that electric guitar through it to see what it sounded like!

My advise would be to have a sensible discussion with the amplifier's owner and explain all the options to them and what the possible effects would be and see what they wanted to do.
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Old 13th Dec 2019, 4:37 pm   #25
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Default Re: Running EZ81 heaters at 5V?

Quote:
That so called 'valve sound' that everyone raves about is generally thought to be caused by rectifier (HT) sag
Have to disagree there Techman, the 'valve sound' is all to do with overdriving the pre and output stage, the rectifier sag is the cherry on top, not the cake. The holy grail of guitar amps is the 1960's Marshall 'Plexi' which had a solid state rectifier

Regarding your last paragraph, I agree and have done so
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Old 13th Dec 2019, 4:52 pm   #26
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Default Re: Running EZ81 heaters at 5V?

Yes, there's a lot of differing opinions on output stages or rectifiers or a bit of both. I've still got a couple of old valve guitar amplifiers that I used back in the day, one with 6 x EL34s and one with 2 x EL34s, both sadly use solid state rectifiers.
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