What do you guys use for toggle switches in HV applications, such as a pentode/triode strapping switch? I may be wrong, but this isn't a trivial application of a standard 250V switch and linearly derating for voltage. I have been burned in the past by what I assume is capacitive coupling through a submini switch and have seen plenty of surplus switches hade of ancient looking dielectrics I wouldn't trust for 400V. Am I wrong?
I have put triode/pentode switches on a couple amps I've built and used regular mini or sub-mini toggles. I just don't switch it with power on. If you want to switch from triode to pentode while the amp is on you should use a switch rated for the voltage it will see.
Given that with a 400V HT, the audio could swing to almost +800V, you're right to be cautious. Whatever type of switch it is, it should have its body securely bonded to the chassis to prevent an internal arc from ending up on the toggle. I'm don't recall seeing any readily available switches that I'd trust. Hopefully, someone will come up with something...
Tweeker said:
Check local code before installing.
I'm sure it would work, but having to put on a suit every time I switched from triode to pentode or back is just too inconvenient...
Hi SY,
You caught me off guard with that one! I needed a laugh! Thanks.
And yes, relays are a very good idea for this.
-Chris
You caught me off guard with that one! I needed a laugh! Thanks.
And yes, relays are a very good idea for this.
-Chris
small togle switches
i use small ones and don't seem to be any problem, i can switch from triode to pentode mode on the fly!
this is my EL84 SET amp:
i use small ones and don't seem to be any problem, i can switch from triode to pentode mode on the fly!
this is my EL84 SET amp:
Won't realys have the same problems? They're rated for 250VAC, and 400VAC (industrial ones) are EXPENSIVE!
To Chris my dear moderator friend, and also to Stuart: look at Tony's amp, my preamplifier (the one you kindly helped me to desing) will be pretty similar/identical in cabinet construction! 😀
To Chris my dear moderator friend, and also to Stuart: look at Tony's amp, my preamplifier (the one you kindly helped me to desing) will be pretty similar/identical in cabinet construction! 😀
A while ago, I looked for relays to switch HV DC (~400V), and they are pretty much impossible to find. Even the 660VAC rated ones are only rated for low DC voltages (28V from memory).
You may get away with switching HV DC with an ordinary switch/relay if the current is low, but it's not likely to be reliable long term. I wouldn't risk it.
I also looked at solid state relays for AC switching, these are quite cool and switch on the zero crossing, but they are expensive.
Cheers,
Pete
You may get away with switching HV DC with an ordinary switch/relay if the current is low, but it's not likely to be reliable long term. I wouldn't risk it.
I also looked at solid state relays for AC switching, these are quite cool and switch on the zero crossing, but they are expensive.
Cheers,
Pete
I thought the DC 28V referred to the relays drive circuitry, and not the rating of the switch? How can a mechanical relay handle 660VAC and not 400VDC?
Hey Tweeker,
It's not so much about making the contact... it's about breaking it.
The current in an AC circuit passes through zero... at this moment, usually, the arc exstinguishes. DC is a whole 'nother matter though. All the same things are going on... vaporized metal (teeny bit), plasma etc... but the current never stops... think of arc welding.
DC relays are often built with permanent magnets, and or an array of metal slats close to the contact path or "swing". The magnetic field serves to stretch the arc out into a loop; the metal slats serve to "tempt" the arc out into a longer path and dissipate some of its energy. All done in the name of breaking the arc sooner and saving wear on the contact. You can guess which contact (pos/neg) catches all the hell... "stripped anode"
Now, you will like this part... some years ago... a guy was successful a creating ball lightning on demand... the technique involved running a locomotive (big DC) at full tilt and then opening the contactors (not normally done... bad train driving). The plasma balls woulds shoot around while the high speed cams caught it all...
😀
It's not so much about making the contact... it's about breaking it.
The current in an AC circuit passes through zero... at this moment, usually, the arc exstinguishes. DC is a whole 'nother matter though. All the same things are going on... vaporized metal (teeny bit), plasma etc... but the current never stops... think of arc welding.
DC relays are often built with permanent magnets, and or an array of metal slats close to the contact path or "swing". The magnetic field serves to stretch the arc out into a loop; the metal slats serve to "tempt" the arc out into a longer path and dissipate some of its energy. All done in the name of breaking the arc sooner and saving wear on the contact. You can guess which contact (pos/neg) catches all the hell... "stripped anode"
Now, you will like this part... some years ago... a guy was successful a creating ball lightning on demand... the technique involved running a locomotive (big DC) at full tilt and then opening the contactors (not normally done... bad train driving). The plasma balls woulds shoot around while the high speed cams caught it all...
😀
Was that Golka?
Thanks for explanation, its not an insulation issue but an arc quenching problem. Theres another approach then Ive seen, a pnuematic or oil hydrallic relay. Oil is probably the better choice here, be pretty silly to have a compressor for your amp.
So hard to avoid Rube Goldbergism. Sigh.
Thanks for explanation, its not an insulation issue but an arc quenching problem. Theres another approach then Ive seen, a pnuematic or oil hydrallic relay. Oil is probably the better choice here, be pretty silly to have a compressor for your amp.
So hard to avoid Rube Goldbergism. Sigh.
I know less about EE than I did on my sixth birthday (destroyed what little common sense I had abusing alcohol) but I'll offer a possibility.
Some time back I was looking for a high current switch to replace the ignition relay on my motorcycle. It's an older BMW and I was having a bad time tracking down ground leaks. I decided to just shut off the main positive right after the battery with a switch hidden under the tank (never had to worry about loosing my key either!). Low voltage, high current dc so I knew I needed something beefy. I found just the thing at the local marine supply. Half a dozen versions of what's called a "main battery switch". Very heavy duty and attractive (they're commonly dash-mounted). About twenty to fifty USD.
I notice tho that they usually are described for "systems under 32 volts" or "systems under 50 volts" etc. So perhaps arcing with higher voltage makes them unsuitable for higher voltage. I dunno.
Some time back I was looking for a high current switch to replace the ignition relay on my motorcycle. It's an older BMW and I was having a bad time tracking down ground leaks. I decided to just shut off the main positive right after the battery with a switch hidden under the tank (never had to worry about loosing my key either!). Low voltage, high current dc so I knew I needed something beefy. I found just the thing at the local marine supply. Half a dozen versions of what's called a "main battery switch". Very heavy duty and attractive (they're commonly dash-mounted). About twenty to fifty USD.
I notice tho that they usually are described for "systems under 32 volts" or "systems under 50 volts" etc. So perhaps arcing with higher voltage makes them unsuitable for higher voltage. I dunno.
Can't remeber who did it dude... I think I saw it Scientific American.
The contactors in power plants have an arm about 12-15 feet long... air actuated... swings open in about 5 ms... timed with AC current. Magnets don't help AC much so the "swing" path is surrounded by "C" shaped slats to disintegrate the arc...
😉
The contactors in power plants have an arm about 12-15 feet long... air actuated... swings open in about 5 ms... timed with AC current. Magnets don't help AC much so the "swing" path is surrounded by "C" shaped slats to disintegrate the arc...
😉
Giaime said:
Use a Mallory "QuenchARC" -- an RC device which prevents you from blowing out the relay contacts.
You can DIY a quencharc by going to their website and just reading the PDF.
You can use any switch safely as long as you have the AC rating... just turned the amp OFF before switching positions... which you should probaly do anyway.
You could even devise a clever interlock.
Arc suppressors will be "in circuit" when you are in pentode mode... so that's out.
You could even devise a clever interlock.
Arc suppressors will be "in circuit" when you are in pentode mode... so that's out.
Yep, AC is a lot easier to switch than DC. Especially if the load is inductive. You will get arcs which will eventually melt the switch.
Yes, this would be fine.
Cheers,
Pete
poobah said:
Yes, this would be fine.
Cheers,
Pete
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