Will any DPDT switch work for pentode/triode switching for a JCM 800 2204 ?

[lemp0-]

Hi , Im a new amp builder , i have only made pedals till now and got my hands on a JCM 800 2204 kit and there is a mod for half power switching and i have a miniature DPDT switch for it, but it is rated at 6A125VAC and Im worried if this would mean that the tube voltages which are 400V+ would damage the switch and hence the amp , Please do tell if this miniature DPDT would be fine for the mod or I need a DPDT switch rated at 400V+ , the ones which are rated at 400V+ are heavy duty toggle switches which are super expensive. Thansk

[pdf64]

250V AC rated switches generally work fine.
But to me triode mode sounds worse. I get the impression most people feel the same.
Plus it inevitably degrades lead dress for perhaps the most powerful electric field transmitter circuit in the amp.
So there’s more useful things you can use a switch for.

[Mick Bailey]

Agreed. 250V AC switches are OK, despite still being under-rated. They last fine, but its important not to flip the switch under load - switching is best done in standby. I wouldn't use a miniature switch due to the possibility of arcing inside the switch body if the switch is operated accidentally under signal conditions. You could add additional protection in the form of a 1M resistor across the terminals, but I still wouldn't recommend it.

Do some research on whether triode operation is for you. It reduces the power, but the sound may not be what you're after and it introduces a lot more hum and noise. The only time I think it does sound good is in HiFi amps that use pentodes.

[Leo_Gnardo]

Agreed. 250V AC switches are OK, despite still being under-rated. They last fine, but its important not to flip the switch under load - switching is best done in standby. I wouldn't use a miniature switch due to the possibility of arcing inside the switch body if the switch is operated accidentally under signal conditions. You could add additional protection in the form of a 1M resistor across the terminals, but I still wouldn't recommend it.

Do some research on whether triode operation is for you. It reduces the power, but the sound may not be what you're after and it introduces a lot more hum and noise. The only time I think it does sound good is in HiFi amps that use pentodes.

I've installed lots of pentode/triode switches, a couple hundred by now. Some players benefit quite a bit, because they can more easily push their amps into clipping plus have a mellower tone while doing it. True, triode mode reduces gain a chunk and also rolls off high frequency response, besides cutting power typically to one third. Less gain? Gotta push the preamp harder - oh boy more crunch! It's not for everybody, and our OP may benefit from auditioning triode mode before he commits to adding a switch.

Also, in triode mode, hum generated is more sensitive to output tube emission mismatches. Best to use tubes closely matched in circuit, or add a bias balance control to fine tune hum from the output. If playing loud all the time is the mode, let it hum, so what.

[Gregg]

Even a cheap 10A DPDT switch will do the job without problems. As a side note APEM switches are rated at 400VAC.