Standby switch location

[Diverted]

I've always wondered about this but never got around to asking until now.
I don't usually put standby switches in the amps I build, but a friend wants one in his.
Now, the few times I've done it, I just put the switch between the rectifier and first filter cap. However I've seen many SB switches that lift the HV secondary center tap from ground.

Any clear advantages of one over the other? Other than less voltage (and AC) on the switch at center tap position?

Ted

[jjasilli]

Search the Forum.

[sluckey]

The voltage across the switch will be about the same regardless of where you connect the switch. Switching the center tap is just as effect as switching the B+ lead. However, there are situations that are dangerous to switch the center tap. DON'T DO THIS IF THE PT USES A SHARED BIAS TAP! Doing so will likely ruin your bias filter caps, causing the bias supply to fail, which will lead to expensive components failing.

[Diverted]

It's a cathode bias amp. I wired it initially on the B+ before the first center tap; suppose I'll leave it that way.

Thanks,

Ted

[pdf64]

Tube or silicon rectification?

[Diverted]

Tube rectified.

[pdf64]

Standby (if it must be included) should be after the reservoir cap then, like the BF arrangement.
Otherwise the rectifier will be subject to excessive surge current drawn by the reservoir cap, every time the standby switch is flipped to operate mode.
It’s referred to as ‘hot switching’ and is poor practice.
Yes, in terms of current flow, your CT switched standby is 'before' the reservoir cap so is of the 'hot switching' type.

See http://www.valvewizard.co.uk/standby.html
A 100k - 47k trickle bypass is a beneficial amendment to the BF standby, and if there's a choke, then a 47nF cap to damp the back emf surge from it when standby mode is engaged.

In addition to the bias supply issue noted above, fusing the HT at the winding CT 0V return is generally poor practice http://www.valvewizard.co.uk/fuses.html http://www.valvewizard.co.uk/fuses.html

[jjasilli]

Could any more be said?  https://el34world.com/Forum/index.php?topic=16773.0

[d95err]

Since the only relevant use for a standby switch is to mute the amp, you could simply wire it as a mute switch, grounding the signal before the PI. I think that’s a more elegant solution than the rather crude switching of the HV supply.

You could still call it ”Standby”. The users would not notice any difference.

[SoundmasterG]

Since the only relevant use for a standby switch is to mute the amp, you could simply wire it as a mute switch, grounding the signal before the PI. I think that’s a more elegant solution than the rather crude switching of the HV supply.

You could still call it ”Standby”. The users would not notice any difference.

Silvertone sort of did this on the 1484 and 1485. It sort of works though if you hit the strings really hard you can hear a quiet farty signal that sounds like a fuzz box with the squelch turned way up.


Greg