a 5ar4 problem

contaxchen · 2005-02-12 11:23 pm

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

SY · 2005-02-12 11:36 pm

Can you sketch a schematic of what you built?

contaxchen · 2005-02-13 3:05 am

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

Layberinthius · 2005-02-13 3:44 am

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.

DigitalJunkie · 2005-02-13 4:10 am

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.

contaxchen · 2005-02-13 4:23 am

Thanks!

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

martinab2 · 2005-02-13 12:04 pm

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?

Giaime · 2005-02-13 1:40 pm

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...

MelB · 2005-02-13 4:52 pm

What is the peak reverse voltage of that bridge recifier? You are probably exceeding it terribly...my guess....... Mel

eds65gto · 2005-02-13 6:16 pm

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

Giaime · 2005-02-13 6:21 pm

He said he didn't have a 5v winding. I suggest to install a small transformer for the rectifier heater. A small 6V trafo will sag quite a bit when supplying an heater, so the voltage will drop to about 5 volts.

contaxchen · 2005-02-14 2:44 am

its not clear from you schematic. I'm assuming that the ht transformer is centre tapped

No, as shown in the picture it doesn't have any center tap. I am thinking about giving up tube rectifiers. That is.
Lhchen

contaxchen · 2005-02-14 2:46 am

What is the peak reverse voltage of that bridge recifier? You are probably exceeding it terribly...my guess.......

I think 530vac is not a problem for 5ar4.
Thanks for replying.
Lhchen

planet10 · 2005-02-14 3:51 am

contaxchen said:
[No, as shown in the picture it doesn't have any center tap. I am thinking about giving up tube rectifiers.

Without a centre tap that circuit won't work... you'd need to use both rectifiers to make a full wave bridge.

dave

Enzo · 2005-02-14 4:16 am

Planet 10 is right, there is no current path through your circuit. But even if you get that right, until you put a filter cap on the output it will still measure high voltage AC since the rectified waveform is a steady stream of half sinewaves.

contaxchen · 2005-02-14 4:52 am

You guys are so right!
After loaded a bleader resistor and a power capacitor, I finally measured the supposed DC voltage at the the capacitor's anode! But, still AC at the 5ar4's output. Wah.... You guys are good!
Thanks,
Lhchen

audiousername · 2005-02-14 7:52 am

martinab2 said:
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?

Nice pick up, Martin

I never thought it was something so basic...

Lhchen, don't give up on valve rectifiers - the transformer is the problem, and not the rectifier. I suppose you could try using two solid state diodes to make a hybrid Graetz bridge rectifier using your transformer without a centre tap. I think you should get 700VDC or so out of it that way.

planet10 · 2005-02-14 9:32 am

audiousername said:
I suppose you could try using two solid state diodes to make a hybrid Graetz bridge rectifier using your transformer without a centre tap.

something like this...

audiousername · 2005-02-14 9:34 am

Yep, that's exactly what I meant!

contaxchen · 2005-02-14 10:10 pm

Lhchen, don't give up on valve rectifiers - the transformer is the problem, and not the rectifier. I suppose you could try using two solid state diodes to make a hybrid Graetz bridge rectifier using your transformer without a centre tap. I think you should get 700VDC or so out of it that way.

I am using that Graetz already. Thanks for the help!
I have never tried this tube rectifier before. It's too much trouble really. I am considering 5ar4 this time, because I got a large Lundahl transformer and a large chassis. There is plenty of power and space to WASTE. :devilr:

Thanks for all the help :wave2:

Lhchen

a 5ar4 problem

Member

Ex-Moderator

Member

Attachments

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

frugal-phile™

Member

Member

Member

frugal-phile™

Attachments

Member

Member