Power relay from 50V bias tap?

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arjepsen
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Power relay from 50V bias tap?

Post by arjepsen »

Hey.
I'm fiddling with my next amp project, and this is the first time for me to use relays.
I've attached a schematic of the circuit I'll be building.

What I'm curious about is how to best power the relay.
I've seen examples of people powering the relays from the heater winding. However, i've also read that this can give trouble with hum.
So I'm wondering whether the same problem would apply, if I use the (unused) 50V bias tap that my PT has (Hammond 372fx) - I think this is tapped off the HT wind, so I wonder if this would still be the same problem with hum.

Also, I've wondered whether it would be better to use a double coil latching relay. Since it only needs to be powered when switching, the extra hum wouldn't be a problem.

What do you guys think??

Regards
Anders
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norburybrook
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Re: Power relay from 50V bias tap?

Post by norburybrook »

I would hazzard a guess that as long as the regulator for the relay sees a voltage within it's spec then there would be no problem.

I have transformers made with extra taps for relays and have no hum problems, your unused 50v bias tap is just another secondary.



MC
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martin manning
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Re: Power relay from 50V bias tap?

Post by martin manning »

I wouldn't be worried about hum, but it's quite a long way from 50VAC (that's 70V peak) to a 5 or 12VDC relay supply. I'd recommend a small auxiliary transformer, u-frame chassis mount ala Dumble ODS, or perhaps a 6VA flat-pack like this one: https://www.mouser.com/ds/2/410/media-1067704.pdf
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Kagliostro
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Re: Power relay from 50V bias tap?

Post by Kagliostro »

At EL34World you can find Relays boards and Relay PS PCB to feed 5v relay starting from 6.3v heaters supply

http://el34world.com/Forum/index.php?to ... #msg139078

K
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xtian
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Re: Power relay from 50V bias tap?

Post by xtian »

martin manning wrote: Sun Feb 18, 2018 3:32 pm I wouldn't be worried about hum, but it's quite a long way from 50VAC (that's 70V peak) to a 5 or 12VDC relay supply. I'd recommend a small auxiliary transformer, u-frame chassis mount ala Dumble ODS, or perhaps a 6VA flat-pack like this one: https://www.mouser.com/ds/2/410/media-1067704.pdf
Showing my ignorance here, but, why would it be “a long way” to create a 5vDC relay supply from a 70vAC source, when we routinely create -30vDC bias supply from 600vAC HT?
I build and repair tube amps. http://amps.monkeymatic.com
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martin manning
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Re: Power relay from 50V bias tap?

Post by martin manning »

It could be done, but you'd have to drop the rectified voltage by more than half just to get to something the regulator could accept (say 30V), and then the reg has to drop that to 5V. Bias supplies use very little current, 2-3 mA. A single relay might be 150mW at 5V, or 30mA.
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