• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Using relays in high voltage circuits

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diyAudio Senior Member
Joined 2002
PROBLEMS ABOUND.

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,;)
 
diyAudio Senior Member
Joined 2002
RETARDED ME.

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,;)
 
Hybrid Rectums

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
 
Ex-Moderator
Joined 2003
More delay

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.
 
diyAudio Senior Member
Joined 2002
6528.

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,;)
 
Ex-Moderator
Joined 2003
Re: 6528.

fdegrove said:
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.

fdegrove said:
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?
 
Only thing I can think of is the low pressure stressing the envelope less, and the changing stress wrecked the vacuum somehow...

Considering the glass is made with equal pressures on either side, and is constructed to have a constant compressive force (about 14PSI, i.e. atmospheric vs. zero), then reducing that force - but clearly not reversing it - can't possibly break the seal.

Were the getters still good before turning it on?

Tim
 
Re: TUBES ON THE RUNWAY.

fdegrove said:
Hi,



Dunno really, it was the only explanation we could come up at the time.
Absolutely nothing was wrong with the amps electrically, the valves were replaced and the problem was gone.

Strange...:(

Cheers,;)

Post hoc ergo propter hoc?

More likely the handling by the chimps working for the airline, I'd expect. Unpressurized cabins didn't seem to bother the tubes used by the Soviets in some of their avionics.
 
diyAudio Senior Member
Joined 2002
PSI.

Hi,

The amps and valves were fine when they left the U.K.

Actually,what may have been the cause of the trouble is the PSU caps in the HT rails not being too happy with the sudden change in atmospheric pressure.

None of the output tubes showed any sign of leakage or air ingress whatsoever...

I think the PSU somewhat got unstable and I was left with a handful of blown fuses (a handful of sand really), endcaps of fuses molten into the partially carbonized fuseholders and a lot of those lovely RCA 6080s with at least one halve of the double triodes gone.

Don't worry too much about it though,;)
 
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