Switch ratings for mods with high voltage

[Jon434]

When the switching involves higher voltages like plate voltage or pentode/triode, or switching between a choke/resistor.. or switching between bias resistors for EL34/6L6.. what's a good rating for the switch? Does it need to be a high voltage switch (like the standby/power switch in most amps) or can it be smaller like the mini switches uses in stompboxes?

I saw the back of Mesa Mark V for example and they use a small switch for triode/pentode and for most of these type of things but I don't know what the actual rating for the switch is, just that it's small. I guess it's because the current is so low? Would a 6A120V 3A250V mini switch be safe to use for something like this? If you used the switches in standby it'd probably put less stress on it? I've also read that arcing can occur, even with higher rating switches, so I'm confused.

I guess having 6A250V or 10A250V would be on the safer side?

If anyone knows a good rating to aim for or any experiences, I've had a hard time finding this information.

[pdf64]

Switches intended for larger ac tend to be slow make/break.
This type of switch action is not suitable for switching dc, which requires a quick action.
So, if the circuit being switched has got significant level of Vdc on it, then find a switch that's rated for 250Vdc rather than 30Vdc, and research the tech info to check it's got a quick action.
Finding a switch rated near 500Vdc is a problem, so as you identified, switches should only be operated when the circuit is at least idle, preferably de-energised.

[trobbins]

One does have to ask whether you really need to switch such circuitry when the amp has operating voltages on it?

[Jon434]

I would only be switching these in standby (or off), but I've read conflicting reports as to whether or not this would matter in terms of the voltage/amps rating of the switch.

I look on the back of Mesa Boogie's Mark 5 or Rectifier and see the bold/spongy switch (variacing to 90V off the PT) or the pentode/triode switch and it looks like a medium/small switch not that much bigger than you see in stompboxes. (edit - bold/spongy does use a larger one) But when others do these mods, they more or less say you should use standby/power rated switches. Which are very large in size and are like like 10A 250V etc.

It would really be good to save space and get the smaller ones, but I have no experience in knowing how safe they could be. I've read some say that they will burn out quicker and need replacing. I want to buy in bulk and trying to plan ahead a month in advance because I've had no luck finding these locally.

Everything I want to switch relates to B+ like chokes, pentode/triode or sag resistors, and the B+ would be off when in standby. But I don't know if there are hazards to using a small switch (just for the current to flow through it) without switching it and if that causes any extra wear or tear? B+ has high voltage but low current, and it's never over an amp? So I'm not sure.

To skip all of the rambling maybe I should just ask the simple question.. if I only switch in standby or with the amp off.. what would be the minimum rating I should look for before ordering?

[trobbins]

The miniature C&K toggle switches have 250VAC 2A rating, with a 1kV dielectric withstand. As such, they would be fine for most static circuit positions (ie. only switch them when amp is not energised). I wouldn't be happy for them in a plate circuit of a higher power amplifier (eg. where B+ is above 500V, and where the plate voltage could exceed 1kVpk repetitively, and easily go higher). Even a plate circuit of a lowish power amp would need MOV type half-primary protection.

Even switches with larger creepage and clearance dimensions should only really be in a plate circuit that has over-voltage protection/limiting added, as transient breakdown arcs may slowly cause carbon tracking breakdown. Some mains switches have withstand DC voltage ratings like 1.1kVDC for 2 seconds, and I could see 1.5kV withstand for large toggle switches.

The whole deal with switch ratings changes completely when you switch energised parts, even when amp is in 'idle', or standby.

[Jon434]

Thanks, that helps a lot.