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Old 8th April 2012, 12:30 AM   #1
Ceglar is offline Ceglar  Australia
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Default Can I delay part of a B supply this way?

I'm needing to delay part of a B supply for a DC coupled amplifier; the input stage plate voltage needs to be at the grid of the second stage before the second stages plate see's any voltage.

Have been using a switch, it works.. but kind of clunky, and the second stage doesnt benefit from any soft start, it just gets 'hit' with 200V.

I'd like to ask if theres any problem that anyone can see with doing it this way. I'm not sure if the diode tube is OK with 260VDC across it, then bring th heater up like this. Any comment is appreciated.

Thanks.
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Old 8th April 2012, 12:38 AM   #2
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If the time delay is to be a bi-metal switch like the Amperite's you'll want to keep current through it to the bare minimum. They arc for the last part of their travel and the contacts degrade steadily. Your circuit probably has a pretty low primary current, but keep some spares for the future.

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Old 8th April 2012, 12:51 AM   #3
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Assuming you're using a solid state bridge rectifier, just the delay of the tube heating up should be long enough without an additional 60 seconds. And a 6087 is an expensive tube to use for this service. There are many other indirectly heated diodes, like damper diodes, to use. Some of them are even slower heating then a 6087. And why heat the filament from the HV side of the bridge?
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Last edited by HollowState; 8th April 2012 at 12:55 AM.
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Old 8th April 2012, 01:20 AM   #4
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There are many other indirectly heated diodes, like damper diodes, to use.
Something like a 6AX4 or, if current production is what's wanted, a Russian 6Д22С (6d22s).
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Old 8th April 2012, 02:48 AM   #5
Ceglar is offline Ceglar  Australia
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Thanks for all the replies, it seems then that the idea will work fine and the diode will be ok with this service.

The time relay is a DIN rail mount CHNT NTE8-480B rated for 5A at 230vAC, so it will be ok with switching the diode heater xfmr primary.

The supply rectifier is pair of 6CJ3 damper diodes, I was going to use 6087 simply because they are on hand along with heater xfmr and the socket. The diodes heater is energised by a heater transformer, so line voltage to the primary of that. Maybe ok without the timer, but its on hand and the first tube is fed from a split rail supply that takes some time to stabilise.. so just to be safe.

6X4.. nice idea.. I have one here somewhere too.. less heater current and a smaller profile.

Thanks for your help, have a nice weekend.
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Old 10th April 2012, 12:54 AM   #6
roline is offline roline  United States
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12AL5 or 6AL5 are still cheep......
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