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Old 12th February 2005, 10:23 PM   #1
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Default a 5ar4 problem

HI all,
I am trying to feed my 5ar4 filament with DC voltage...., since my transformer doesn't have any 5vac winding. It turns there is no DC output at its cathode! I only measured 260AC at its cathode. It's like the rectifier got no function at all. The DC pass the tube directly! What gives? I flow the filament supply. It should be OK.
Lhchen
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Old 12th February 2005, 10:36 PM   #2
SY is offline SY  United States
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Can you sketch a schematic of what you built?
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Old 13th February 2005, 02:05 AM   #3
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I measured around 250vac at foot 2 and 8 of 5ar4. Where is my dc output? I didn't ground the filament... and no load at all
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Old 13th February 2005, 02:44 AM   #4
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I'm going to assume there is internal damage to the rectifier tube, between cathode and one of the plates...


Swap out the tube and try another one.
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Old 13th February 2005, 03:10 AM   #5
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be sure your rectifier and regulator are floating... The 5Vdc supply will be up at B+ voltage.

With a normal AC tranny winding,the 5V winding is isolated well,and floats at the rectifiers cathode voltage.
Unless of course you have an IDH-rect,with a seperate cathode pin.
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Old 13th February 2005, 03:23 AM   #6
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Default Thanks!

Quote:
I'm going to assume there is internal damage to the rectifier tube, between cathode and one of the plates...
I have tried the second one, but the problem is still there...
I do float the filament supply...
This is interesting. Anybody else? I have only two 5ar4.
Thanks.
Lhchen
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Old 13th February 2005, 11:04 AM   #7
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Ok, this might be a silly question... but its not clear from you schematic. I'm assuming that the ht transformer is centre tapped with the centre connection being the negative side of your circuit. Can you confirm that this is the case?
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Old 13th February 2005, 12:40 PM   #8
Giaime is offline Giaime  Italy
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Remember that often DMMs actually DO measure an AC when there is DC... But also remember that at the output of a rectifier you won't see DC or AC... they are just pulses... Try to filterit with the proper capaicitors and measure then... maybe an oscilloscope will tell what's goin on there...
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Old 13th February 2005, 03:52 PM   #9
MelB is offline MelB  Canada
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What is the peak reverse voltage of that bridge recifier? You are probably exceeding it terribly...my guess....... Mel
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Old 13th February 2005, 05:16 PM   #10
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Default 5AR4

My only question is WHY????
You do not need DC on the rect filament. Just hook the rect. to the 5V winding. The output comes off of the cathode-heater pin.
Your schematic does not show a center tap on the HV secondary. This must be connected to ground to get a positive voltage at the cathode of the rectifier.
There will be pulsating DC at the cathode. This requires filtering to be used.
Hope this helps
Ed
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