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Old 21st July 2007, 02:22 AM   #1
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Default B+ Delay

What do you think about just putting a dpst switch in line with the 5v winding so the 5v4g doesn't rectify, and then just closing the switch after about 30 seconds. Will the 5v4g act as an open without 5v applied? I'm new to tube audio, and this is my first project. Any other suggestions would be appreciated!

Thanks

Dave
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Old 21st July 2007, 02:32 AM   #2
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A switch is unnecessary and could be dangerous. The 5V4 has a cathode sleeve; so, it's inherently slow starting. While there is nothing exciting about 5 VAC, you are ignoring the fact that the winding is (SIC) at B+ potential. An "ordinary" toggle switch could easily arc over to chassis.
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Old 21st July 2007, 02:34 AM   #3
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Everything you said is correct, and I'm disappointed with myself for not thinking of it sooner, but there's one kicker in it.

What will be the effect on the rectifier of having full voltage on the plates with a cold cathode?

That's the only thing I see.

Aloha,

Poinz
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Old 21st July 2007, 04:05 AM   #4
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Such is the fate of rectifiers, Poinz. It can't be helped. If the 5V4 doesn't like it, then it shouldn't have signed up in the first place.
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Old 21st July 2007, 04:45 AM   #5
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Raymond, you shame me. Of course, that is the rectifier's life in a nutshell. B+ main on the plates from the flip of the switch, this until the cathode heats up, then SHOWTIME!

I love showtime. Right now, Claremont Duo, Radames Gnatalli 'Sonata'.

Effing fabulous.

Don't y'all get blown to bits there, now.

Poinz
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Old 22nd July 2007, 09:40 AM   #6
billr is offline billr  New Zealand
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Default Re: B+ Delay

Quote:
Originally posted by habsrock93
What do you think about just putting a dpst switch in line with the 5v winding so the 5v4g doesn't rectify, and then just closing the switch after about 30 seconds. Will the 5v4g act as an open without 5v applied? I'm new to tube audio, and this is my first project. Any other suggestions would be appreciated!

Thanks

Dave

an easier way is to put a switch in the earth centre tap

bill
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Old 23rd July 2007, 06:53 AM   #7
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Quote:
Originally posted by Poindexter
Everything you said is correct, and I'm disappointed with myself for not thinking of it sooner, but there's one kicker in it.

What will be the effect on the rectifier of having full voltage on the plates with a cold cathode?
There may be a possibility for cathode stripping. However, that's how they've been running them all along back in the good ol' days, and I don't recall ever reading that it was a problem.

However, Hg diodes are a whole 'nother story. These must have filament preheating before you hit 'em with the HV, otherwise, you will ruin them in no time.

Otherwise, I use preheating if using a SS power supply. With SS diodes, the HV comes up within a second or two. Not enough time to allow cathodes to get hot enough to pull significant current. Otherwise, doanworrybouddit
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Old 23rd July 2007, 08:30 AM   #8
arnoldc is offline arnoldc  Philippines
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The Morgan Jones Valve Amplifiers 3rd edition has great techniques on this issue..
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Old 23rd July 2007, 06:54 PM   #9
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Quote:
Originally posted by Miles Prower


There may be a possibility for cathode stripping. However, that's how they've been running them all along back in the good ol' days, and I don't recall ever reading that it was a problem.

Irradiated doseage strip-tease ?
I do recall some 1950's TV sets with line o/p tubes which had a skull and crossbones on it and for worse no colour.
True true..it wasn't a problem. Generous coating of emissive materials were put on directly heates cathodes, even some were radioactive, manufacturers went to whatever trouble to race ahead of the competition.

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