Switch for High Voltage AC

[TheTinMan]

Does anyone know of a 2-pole, triple throw toggle switch with On-Off-On function rated for 350 volts or more AC?

I'm getting a power transformer that has two sets of HV secondaries:
330-0-330
355-0-355


Since I don't need a Ground switch, I thought I could use that hole in my 5E3 chassis to switch between the lower and higher PT secondary windings. However, I haven't been able to find a suitable switch that doesn't cost a small fortune.

Please refer to attached power supply schematic. AC voltage rating is serious constraint for my switch. Would it help to have four diodes instead of two and have the switch between the diodes and the rectifier tube? (instead of between the power transformer and the diodes) My thought is that the switch would be handling "DC" instead of "AC" with four diodes.

BTW the diodes are there as protection in case of rectifier tube failure - see "Immortal Amp Mods" #1.

Any ideas or suggestions?

It doesn't have to be a toggle switch. Rotary or rocker would work. I guess On-On (On-none-On) function would work, but it would need to be "break then make" connection unless I'm mistaken.

Chip

[Jazz P Bass]

H-Series | carlingtech.com

[R.G.]

I would go with a solid state relay (SSR) or some high voltage triacs and optoisolator drivers. High voltage switches are expensive, and there is always some issue with safety wiring.

The triac solution is the lowest cost one, although it also has its issues with safety and isolation. But the optos mean you can do your manual switching with a low voltage (and cheap!) switch. Mouser has 1kV Triacs that will support up to 4A for under $1.00 each, and zero-crossing triac drivers for $0.80 to $3.00 each. So you could make each switch section cost ~ $2.25, and drive the LEDs in the optos with a low voltage switch.

SSRs are easier to wire up, but more costly.

All this is deadly dangerous, of course, but you're already up to your elbows in hazardous voltages, so I'm going to assume you'll survive the encounter.

[eschertron]

+1 to avoiding a brute-force method in favor of controls. However, for the HV switch option:

Another operational possibility is to NEVER toggle the switch with power on the secondaries. This makes the 'switching voltage' rating moot. You'd still need to verify isolation voltage and current capacity for the switch in question.

Since NEVER is likely to be a long way off, realize that AC ratings are often higher for any given switch than DC ratings. It may be easier to source a switch if you consider that.

[TheTinMan]

Thanks guys!

eschertron - I've been considering the "brute force method" but do NOT like the idea of building an amp where really BAD things could happen with the wrong manipulation of switches. However, this may be the way to go just for purposes of comparing the two voltage levels on a temporary basis. IOW prototyping then taking the darned thing (switch) out after choosing the voltage level I prefer.

R.G. I especially appreciate you offering two or three safer alternatives. Unfortunately, I simply am ignorant when it comes to solid state electronics.

I'm not certain that being able to switch in higher voltages would be useful enough to justify the effort to do it safely. Especially given the lack of real estate inside a 5E3 chassis. Nevertheless, I am grateful to you all sharing your thoughts with me.

Respectfully,
Chip

[pdf64]

Does anyone know of a 2-pole, triple throw toggle switch with On-Off-On function rated for 350 volts or more AC?

What exactly do you wish to switch and to achieve, eg most pertinently, what are the 2 'on' states?

[TheTinMan]

What exactly do you wish to switch and to achieve, eg most pertinently, what are the 2 'on' states?

Please see schematic attached to original post.

[pdf64]

Sorry I missed the attachment.
Given the heavily reactive nature of the load, a slow make/break type may not be ideal.
I suggest a quick make / break type, eg switchcraft 110 series, in order to nip arcs in the bud, rather than use slow, very heavy duty contacts to promote but hopefully withstand them.

[g1]

How often are you going to want to change voltage? Does it really need to be accessible from the outside?

[nickb]

Can I ask, why?

We are talking about a 25/330 or less than 10% change. In terms of power out it's less than 1db. You won't notice it.

[J M Fahey]

That's the point.
Difference in power/volume is inaudible (don't trust me, test it) , so just pick one.
personally, I'd pick the (slightly) lower one, which stresses everyting somewhat less for practically the same sound/volume.

I do what I preach: I made thousands of SS amps since 1969 (way over ten thousand) , originally starting with +/- 35V rails (using 2N3055 "by the book"), then started selectingb them and slowly creeping rail voltages up, so rising power.
My nominal 100W amps ended putting out some 130W RMS (into 4 ohms) .
Then fake 2N3055 started apppearing everywhere around 2005/2008 and even real ones (ON - ST - Fairchild), thanks to cut throat competition started to *just* match datasheet specs so were useless for me, even worse useless to repair my own old amps (had to upgrade to way more expensive MJ15015 or 15003 or 1502x for servicing).

So gradually lowered rails to present +/-38 or 39V ... amps now *barely* make 100/4 and sometimes only 95/4 .

At the bench, 95W is abysmal compared to 130W, huh?

Well, not one customer ever complained about "low power" , how's that?

So I guess you shouldn't worry

There's so many other factors involved (many speaker or EQ related) that really minor measured power difference get lost in the chaff.

[TheTinMan]

Can I ask, why?

We are talking about a 25/330 or less than 10% change. In terms of power out it's less than 1db. You won't notice it.

"Why?" Before I realized how difficult it would be to switch high voltage safely, I thought "why not?" since the ClassicTone PT with the lowest ma power rating has both taps.

From all the threads out here in cyberspace about getting voltages "right" for the 5E3 circuit it seemed like making it switchable might be useful. Plus there's that empty hole for the Ground switch with lots of high voltage AC and heavy currents nearby. IOW far from an ideal location for a master volume, presence control, etc.

I know that dropping the B+ by less than 50 volts in a 5F2-A type circuit made a big difference in feel and clean headroom. Yes, I used that awful word to refer to the volume level where the amp starts breaking up.

Based on this discussion, I'm abandoning the idea - at least of doing it the way I originally thought of.

How often are you going to want to change voltage? Does it really need to be accessible from the outside?

I think this implies the best answer. Thank you. I'll wire it up with the 330-0-330 taps but do it in a way where changing to the 355-0-355 taps is easy. Play for a while and then decide whether or not to mess with it at all. If the higher voltage seems useful for some circumstances, then I'll re-visit the idea of making it switchable using one of R.G.'s approaches or his MOSFET-zener power scaling or something else...

Thanks,
Chip

[frus]

From all the threads out here in cyberspace about getting voltages "right" for the 5E3 circuit it seemed like making it switchable might be useful.

In my experience, one position will sound better (to you subjectively, of course), and you'll never switch it again

[potatofarmer]

So far no-one's mentioned the risks of hot-switching with a tube rectifier. In a nutshell: tube rectifiers don't like it and can express their displeasure by arcing.

Even adding the external switch but never intentionally flipping it still leaves the possibility of it getting bumped. Not a risk I would take if you're going to use the amp for gigging, particularly since a well-meaning stranger may mistake it for a standby switch.

The Orange Tiny Terror uses an additional tap on the PT for "half power" mode, but with a bridge rectifier. Also I imagine the taps are more significantly different than on the OT mentioned in the original post, though I can't find the specs.

[TheTinMan]

So far no-one's mentioned the risks of hot-switching with a tube rectifier. In a nutshell: tube rectifiers don't like it and can express their displeasure by arcing.

Even adding the external switch but never intentionally flipping it still leaves the possibility of it getting bumped. Not a risk I would take if you're going to use the amp for gigging, particularly since a well-meaning stranger may mistake it for a standby switch.

The Orange Tiny Terror uses an additional tap on the PT for "half power" mode, but with a bridge rectifier. Also I imagine the taps are more significantly different than on the OT mentioned in the original post, though I can't find the specs.

Very good point about switching HV secondaries while rectifier has hot heaters. Can't be a good idea.

Thanks,
Chip