relay power methods

[phsyconoodler]

I have a pt that has no 5v taps for relay power and i dont have enough room current wise to use the heater taps. Can i just use a half wave rectified source from the pt secondary?

[sluckey]

You talking about the high voltage secondary? I would not do that. Each of Doug's tiny 5 volt relays requires 40mA to operate. That's a lot of extra current load on a high voltage winding. Are you sure you don't have enough current available in the 6.3v winding? Even 7 relays energized at the same time would be less current demand than one 12AX7. Even if I was maxed out on the 6.3v winding, I would not hesitate to tack on a couple of Doug's small relays.

[phsyconoodler]

Ah the current i wasn't thinking about. I will likely be safe with the heaters

[PRR]

You can get 28V and 120VDC relays which will take proportionately less current.

It is still a long and wasteful drop-down from 300-400V supply. If you use a dropping-resistor to get a happy relay-voltage when ON, in the OFF condition the full 300+V appears across your switch, which may raise safety or rating concerns. A regulated supply is really getting messy. I'd throw a 6V 0.3A filament transformer on the chassis before I'd run relays from power-amp plate supply.

[EL34]

There's always enough current capacity in the heater winding for one small signal switching relay like the ones I sell
Unless of course the heater string is maxed out and running super hot as it is
In that case, there's way more to worry about