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Old 10th June 2013, 03:51 AM   #1
tubo is offline tubo  Philippines
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Default HV delay switch

Hey Folks,

Can I install a switch between the HV secondaries before the rectifier to let the rectifier warm-up before applying the high voltage? Ive seen some scheme that use those but I cannot find a DPST OR SPST switch that goes above 250v in rating. Do you guys know where to get one?

Last edited by tubo; 10th June 2013 at 03:57 AM. Reason: unfinished post
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Old 10th June 2013, 04:22 AM   #2
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Delaying AC power to the rectifier plates is usually unnecessary if you're using a standard vacuum type. If mercury vapor, then yes it's necessary to delay. If you just want to save a little wear and tear on the tube, then you could put SS diodes in series with the plates and the transformer winding. But if you insist on a switch, then it's best to use a relay. Either manually turn it on/off with a smaller switch, or use a seperate or internal time delay circuit. The contacts will withstand hundreds of volts. I'd look on eBay for the better prices.
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Last edited by HollowState; 10th June 2013 at 04:41 AM.
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Old 10th June 2013, 05:10 AM   #3
DUG is online now DUG  Canada
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HV relays are expensive.

Kilovac make some.

Or look at these available at Digikey:

Signal Relays, Up to 2 Amps | Relays | DigiKey

Be careful.

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Old 10th June 2013, 05:45 AM   #4
tubo is offline tubo  Philippines
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Thanks for the input fellas. I was planning on subbing an 83 mv rectifier in place of a 5u4g in my se amp without resorting to a separate filament transformer. The power supply have clc arrangement and I was thinking of just adjusting the first cap to get the right voltage if I use the 83.

Without a separate filament transformer for the 83, where is the best place to put a switch to let its filament warm-up before applying hv? I can't think of a place where to put them but before the rectifier ,n I dnt want to deal with relays.

I think its time to find a 5vct filament transformer.
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Old 10th June 2013, 10:56 AM   #5
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Just put a delay relay in before the 83.

Switching AC is a simple task for a relay.

Set the delay for enough time to let the 83 warm up.
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Old 10th June 2013, 11:26 AM   #6
FoMoCo is offline FoMoCo  United States
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Here's a recent thread where we discussed the problems of switching HVDC: Relays for tube voltages
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Old 10th June 2013, 11:40 AM   #7
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Quote:
Originally Posted by FoMoCo View Post
Here's a recent thread where we discussed the problems of switching HVDC: Relays for tube voltages
With a MV tube you donīt want to switch the DC.

Switching DC is a more complicated task since relays cope with less DC then AC voltage.

Switch the AC going into the tube !
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Old 10th June 2013, 12:02 PM   #8
FoMoCo is offline FoMoCo  United States
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Quote:
Originally Posted by flatheadmurre View Post
With a MV tube you donīt want to switch the DC.

Switching DC is a more complicated task since relays cope with less DC then AC voltage.

Switch the AC going into the tube !
That was our point in that thread. However, there was a solution found to switch DC that seems like it'd work. Someone here may (or may not) find it useful. I've always thought "Never switch DC" and was surprised.
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Old 10th June 2013, 12:11 PM   #9
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Quote:
Originally Posted by FoMoCo View Post
That was our point in that thread. However, there was a solution found to switch DC that seems like it'd work. Someone here may (or may not) find it useful. I've always thought "Never switch DC" and was surprised.
Iīll better read up then, the only thing working for dc i know of is the vacuum switches iīve "borrowed" from work and they cost an arm and a leg....
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Old 10th June 2013, 12:38 PM   #10
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Hi!

For a MV rectifier like the 83, delaying the HV AC until the mercury is vaporized is a good practice and actually required to avoid arc over at start up. This can be easily done by putting the switch in the ground return to the transformer secondary center tap (if you use a FW rectification scheme with center tap)

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