Standby switch question

[Matt T.]

Can you safely switch a tube amp from Standby to ON by using a DPDT switch, one pole for the OT center tap and the other pole for the screen voltage? Any 'issues'? I have a reason for 'needing' to do it this way (power scaling). But I was concerned about the screens (or an over-sight lol)...which by-the-way will have separate 1K/5W screen grid resistors.

Also, would it still be OK (perhaps even preferable?) to put snubber caps across the SB switch lugs to prevent pops?

TIA.

[Ray Ivers]

Matt,

How about connecting a 4.7K 1W resistor from all (paralleled) output cathodes to ground, and then switching this in and out using a simple SPST switch? This allows a trickle of current to flow during standby to prevent cathode poisoning, with no cap-charging surges.

Ray

[Matt T.]

Ray,
Actually all the caps would already be charged. Basically; turning the power switch ON would turn the entire amp on, all caps charged, even preamp tubes running. Then the SB switch would connect the OT center tap and screens to their respective filter caps.

Or I could do it the way you describe if you still think that's better.

[Ray Ivers]

Matt,

the SB switch would connect the OT center tap and screens to their respective filter caps

That should work. You'll still have full cathode temperature with no current flow thru the tube, but if that's not a concern, go for it!

Ray

[Matt T.]

FWIW, I did build this amp with the standby switch outlined above and it worked...the power tubes don't even do any sort of 'dance' (with blue glow or whatever)...the sound just abruptly cuts in/out as you flip the switch. It seems with Fenders, the power tubes always do a 'dance' as in...you could tell when the standby switch was thrown just by looking at the power tubes (but my particular amp is only 395vdc Va).

But there was a decent pop/thump when you flipped it so I put a .01uF/1kV cap across the terminals for each pole of the switch and now it's a completely silent turn-on.

All that for a switch that I technically never needed in the first place.