Using relays in high voltage circuits

[fdegrove]

Hi,

But wouldn't it be a problem to use 'normal' switches in high voltage circuits too??

Normally you only have to consider the current ratings of that "normal" switch.
Unless specified explicitly you can derate easily using Ohm's law.

With relays it is a different story, if you consider what they consist of I'm sure you'll understand why.

Cheers,

[316a]

Out of interest , would a tube thermal delay such as VLS631 be ideal or are these things too puny ?

316a

[fdegrove]

Hi,

Out of interest , would a tube thermal delay such as VLS631 be ideal or are these things too puny ?

I never heard of the VLS631, but anyone smart enough can build a hybrid rectumfryer providing the best of both worlds.

1/Vacuum tube rectifiers have slow start built in.

2/I use solid state rectification and still want a slow turn on, what to do?

A:use a thermistor, use a tube voltage reg.,use your hands and switch the heaters on prior to the B+...

Countless possibilities really, a relay would be the last of my options.

BTW, only when solid state rectification is used can a turn-on delay be justified....most of the time though I can't be bothered.

Cheers,

[316a]

Hybrids work fine , I have found that the otherwise useless PY500a with solid state works particularly well . Even the solid state 'gyrator' or 'active capacitor' has it's uses , I've never had luck with mosfets here and my bipolar darlington design goes west over 400V but they do work very well if you don't take the **** out of them . A PSE 845 amp with a large 'frankenstein' knife switch on the HT would really get the adrenaline flowing though !

316a

[slowmotion]

A PSE 845 amp with a large 'frankenstein' knife switch on the HT would really get the adrenaline flowing though !

Ahh, cool

[EC8010]

Although valve rectifiers switch on gently, they don't necessarily give all the delay you need. Putting a thermal delay relay in series with the rectifier's heater adds the two delays together and ensures a nicely delayed soft start for fragile valves like 6528.

[fdegrove]

Hi,

delayed soft start for fragile valves like 6528

Really?

I'd like to know more about that,pls.

Cheers,

[EC8010]

Yes, in the Tung-Sol/Chatham data sheet, the Application Notes recommend a 30s cathode warm-up time before applying anode volts. But I've measured valve rectifiers beginning to conduct rather sooner than that...

[fdegrove]

Hi,

Well yes, most regulator valves suffer from this actually.

Come to think of it, low Ri, low mu, highish transconductance...asking for trouble when the B+ is slammed on, right?

The biggest mess I was ever in was when my amps were flown back in from Birmingham and as I lived only ten miles from the airport I switched them on half an hour later.

Wow...they all went into thermal runaway within ten minutes.

Stupid really, should have thought about the luggage department not being pressurised.

Cheers,

[EC8010]

Originally posted by fdegrove
Well yes, most regulator valves suffer from this actually.

Come to think of it, low Ri, low mu, highish transconductance...asking for trouble when the B+ is slammed on, right?

Yes, I wondered whether this might be a universal problem for high gm valves. Anyway, I've come to the conclusion that unless you are using disposable valves, there always ought to be provision for being gentle at start-up.

Originally posted by fdegrove
The biggest mess I was ever in was when my amps were flown back in from Birmingham and as I lived only ten miles from the airport I switched them on half an hour later.

Wow...they all went into thermal runaway within ten minutes.

Stupid really, should have thought about the luggage department not being pressurised.

Am I missing something obvious here? Why would an unpressurised hold cause thermal runaway later?