285v dc on front panel mini toggle

[Ecs787s]

Hey Guys, I'm working on a UA176 right now and am wondering if there is any problems with using a mini DPDT toggle switch to select between two different ratios (instead of the original 4 ratio settings on a rotary switch). This switch feeds the two sidechain capacitors, so only ac will be brought to the 6al5 rectifier tube after those caps.

I assume the dc doesn't have any current flowing through the switch because of the blocking capacitors, so it just sits there. I assume that most switches are really rated for Power (wattage) and not just voltage or amperage? The wattage is what would melt it right?

Can anybody comment on this regarding safety or weather that switch will have any issues in the future?

I have already built one of these in this fashion and haven't had any problems but want to know whether I should change things around on the second build.

 

[JohnRoberts]

Switches are not rated for power but voltage and current. The voltage is related to safety spacing between contacts and to chassis ground if metal bushing. Current affects contact resistance.

Use a switch rated for more than the voltage you anticipate.

JR

 

[jwhmca]

Switches are not rated for power but voltage and current. The voltage is related to safety spacing between contacts and to chassis ground if metal bushing. Current affects contact resistance.

Use a switch rated for more than the voltage you anticipate.

JR

Also, the current level speaks directly to how much "arcing" it can handle when you open the switch contacts. DC can make a longer, hotter arc when you open the switch. AC has a high chance of being at the zero point when you open the contacts. That's why you see switches rated for HIGH AC and LOW DC. e.g. 250 AC- 28 DC... Right?

 

[JohnRoberts]

While I am a little outside my area of expertise, AC seems like it would be self quenching. Even if an arc and ionized path keeps conducting, when that AC voltage passes through zero the arc should stop conducting.

For the OP this seems like a safety spacing for breakdown voltage issue, and voltage higher than normal low voltage switches.

JR

 

[jwhmca]

...AC seems like it would be self quenching. Even if an arc and ionized path keeps conducting, when that AC voltage passes through zero the arc should stop conducting.

said better, but that's what I was saying...

Call NKK, or any of them, talk to their design engineers...

 

[Ecs787s]

Thanks for the replies everyone... I need to correct myself and say it was not a dpdt, but a 3pdt switch. I guess I was just curious about how Universal Audio did it back in the day. They had DC going straight to the switch and the blocking capacitors after the switch before the AC audio signal was rectified. That's why I asked if the current had anything to do with the ability to put such high DC on the switch,I've attached the schematic. Caps C6 and C7. I think I'm going to put the caps before the switch so that no high DC can get to the switch. Obviously I would have to use more caps, but for as cheap as they are vs. injury, it is worth it.

Any other thoughts?

 

[sodderboy]

I would put a relay board close to the circuit with 2 DPDT relays at proper rating, or there are plenty of 4PDT relays available as surplus. Those mini toggles and >100 volts?  Not on my builds.
Mike

 

[emrr]

The original switch type handles much more than a modern small toggle. 

 

[My3gger]

Don't know where you live, in Europe are easy to get those blue Miyama switches, they are much better than cheap Chinese copies with similar look. Miyamas have each "soldering contact" (where you attach wires) separately potted with ceramic, 250VAC/3A rating and are well made. IIRC, breakdown voltage is 1kV for Miyama MS500 series, but please check datasheet to be sure. 4PDT model is this:
https://www.tube-town.net/ttstore/product_info.php/info/p5414_Miyama-Toggle-Switch-MS500P-4PDT-ON-ON.html
I also used Carling which were bigger and more expensive, don't know if you can find 4PDT. As for shops in EU, i would avoid Banzai...
Good luck with your project.

 

[rafafredd]

WOW, where did you got that output transformer with the multiple ratio switches????

I say just move it to the other side of the caps. Should make no difference in function, and you get only 45v on the switch.

 

[Ecs787s]

Yep, that is what I did and it worked fine. The output transformer is an Edcor that has the 40% screen tap... it works like a charm. So I have a ratio of around 10:1 and one around 5:1 at 10dB of gain reduction... lower ratios with lower amounts of gain reduction.

Thanks for the replies guys.