Whilst browsing AliExpress I came across a 0 to 500V DC voltmeter for around £2 delivered!
That got the cogs whirring so I bought one, attached it to a PP3 and fixed it into the amp that I'm working on as a gentle reminder that these things aren't always gentle.
It was surprising how slow the B+ decays, there is still a considerable voltage after a few mins, admittedly there's no tubes in at the moment.
As you can see from the pictures, it is surprisingly accurate too.
Craig
£2 Safety Device
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CraigGa
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£2 Safety Device
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Thinking about my second build.
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Stevem
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Re: £2 Safety Device
Well even if the tubes where in, but with no filament heat in them to conduct with the V+ voltage will sit up there for a while if the filters are good and there’s no bleed resistor anywhere in the circuit to act as a drain.
With most amps that have a separate standby switch if you turn off the power switch first then the conduction heat that’s left in the tube filaments will drain the power supply down to about 70 volts within 2 minutes and the amp will then be safe to work on once unplugged from the wall power.
With most amps that have a separate standby switch if you turn off the power switch first then the conduction heat that’s left in the tube filaments will drain the power supply down to about 70 volts within 2 minutes and the amp will then be safe to work on once unplugged from the wall power.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: £2 Safety Device
Yes it goes down to safe levels pretty quick with all the tubes in but I'll still find it a useful reminder when I'm playing inside amps.
Craig
Craig
Thinking about my second build.
Re: £2 Safety Device
I don't know for sure that it was the first time anyone had ever used the idea, but I put LEDs in series with the safety drain-down resistors parallel with the main filter caps on the Workhorse line of amps. If there was enough voltage there, the LED was lit, albeit dimly. LEDs lit, it's still dangerous. LEDs out, it's probably early drained down. Not as accurate as a voltmeter, but it only took up 5mm diameter on the main board.
"It's not what we don't know that gets us in trouble. It's what we know for sure that just ain't so"
Mark Twain
Mark Twain
Re: £2 Safety Device
I never knew you designed those amps. Cool!
https://tfrelectronics.com/
https://oshpark.com/profiles/TFRelectronics
https://oshpark.com/profiles/TFRelectronics
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SoulFetish
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- Location: Norwood, MA
Re: £2 Safety Device
It has the hallmarks of a great idea. It’s simple, clever, inexpensive, and useful. I wish I’d thought of itR.G. wrote: ↑Sun May 30, 2021 10:37 pm I don't know for sure that it was the first time anyone had ever used the idea, but I put LEDs in series with the safety drain-down resistors parallel with the main filter caps on the Workhorse line of amps. If there was enough voltage there, the LED was lit, albeit dimly. LEDs lit, it's still dangerous. LEDs out, it's probably early drained down. Not as accurate as a voltmeter, but it only took up 5mm diameter on the main board.