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Damper diode slow start

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Strange.. the 6AX4/6DE4/6DM4 type is pretty good and has a similar warm-up time as 6AU4.

If you are getting flash-over, then maybe you should swap them out for different ones? I have a huge box of them and after 40+ years not all are good.

How are you using it? Two in full-wave rectification or did you build a bridge with 4 of them?

or are you doing silicon rectification and just using one in series? Maybe you can post a schematic...
 
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Provided that the tubes are not defective, arc-over or flashing in a MV rectifier is a design problem which should be corrected. Application of the plate voltage must be delayed but maybe the warmup time of most damper diodes in not sufficient to allow full vaporization of the mercury. It is also possible that some other maximum ratings (peak current...) are exceeded. And if you need to use damper diode tubes ahead of the M.V rectifiers to delay plate voltage I don't understand why you still need the M.V tubes in the circuit. This seems an unnecessarily complex way to accomplish a simple task (rectification). Maybe you could post your circuit so we can have a clearer picture and help you more efficiently.
 
Strange.. the 6AX4/6DE4/6DM4 type is pretty good and has a similar warm-up time as 6AU4.

If you are getting flash-over, then maybe you should swap them out for different ones? I have a huge box of them and after 40+ years not all are good.

How are you using it? Two in full-wave rectification or did you build a bridge with 4 of them?

or are you doing silicon rectification and just using one in series? Maybe you can post a schematic...

Thanks for your comments.

I tried some other tubes in my stash and it looks like it may have been a defective tube, even though it was new. I gave it a 10 minute warmup before I applied any HT.

I built a hybrid bridge with two 816s and two UF4007 diodes. It's choke input (5Hy) and has two stages of 100uF electrolytic with the second stage being RC.

I haven't really drawn a schematic, just wired it on my bench to prove the concept would work. It's overkill for what I'm building, but the customer wanted MV tubes for the blue glow, so that's what I plan to give him.
 
Provided that the tubes are not defective, arc-over or flashing in a MV rectifier is a design problem which should be corrected. Application of the plate voltage must be delayed but maybe the warmup time of most damper diodes in not sufficient to allow full vaporization of the mercury. It is also possible that some other maximum ratings (peak current...) are exceeded. And if you need to use damper diode tubes ahead of the M.V rectifiers to delay plate voltage I don't understand why you still need the M.V tubes in the circuit. This seems an unnecessarily complex way to accomplish a simple task (rectification). Maybe you could post your circuit so we can have a clearer picture and help you more efficiently.

I'm building a hybrid bridge with two 816s and two UF4007 diodes. I'm using the damper diode with the cathode wired to the power transformer center tap and the anode grounded. I've done this with 6D22S dampers before and it worked well with 866As. I want to use an octal ST shaped tube with this design.

My voltages are comparatively low, only about 210VDC, so I don't think I'm exceeding the 816's specifications :) My customer wanted the blue glow and 816s look nice.
 
Seems these needs some care, 0,5A peaks are not uncommon
 

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This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.