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Old 30th November 2006, 01:23 AM   #1
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Default Rectifier that drops lots of volts?

I am having trouble sourceing the power transformer I want. A 250-0-250 with a gz34 gives me about the voltage I want, but the only thing I can find is 300-0-300 (I am looking for a James to match the OPTs, and euphonia is out of stock and no one else (James/THL, and a few others) will answer my emails). So, I am looking for an octal rectifier tube that does not need more than a 5V/2A winding that can drop a few more volts. Any suggestions?
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Old 30th November 2006, 01:34 AM   #2
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use LC filter
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Old 30th November 2006, 01:39 AM   #3
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Try a 5U4? This is PSUDII right? Is there no way you could sneak a little 3-amp filament transformer under the hood of the amp? I don't know any rectifiers that fit your criteria otherwise...

edit: or a LC filter. What is the desired voltage and current?
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Old 30th November 2006, 02:01 AM   #4
kevinkr is offline kevinkr  United States
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5R4...
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Old 30th November 2006, 02:07 AM   #5
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I've been working with the GZ34 (5AR4), 5R4 and 5U4GB. I can get the VDC I need from the GZ34, and the others (both directly heated) give quite a bit less, due to a voltage drop that kicks in depending on the current drawn. Try a 5R4 with a 10H choke in LC, adding an input cap well *under* 4 muF. The 5U4GB may give you a little more output (but maybe not much when under load).

As an example, in one case I got 352 VDC under load with the GZ34, and 328 VDC with the 5R4. You can source all these from Jim McShane.
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Old 30th November 2006, 04:51 AM   #6
Tweeker is offline Tweeker  United States
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I have 240-0-240 (read: industrial control transformers) PTs coming out of my ears. Although, they arnt purty like the James.
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Old 30th November 2006, 05:26 AM   #7
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Yeah, this is really all about purtyness. here's the "breadboard" version of the amp

Click the image to open in full size.

and that Hammond is just ruining it. I have a fancy padauk case made and am getting the top plate machined professionally, so it just seems wrong to not have a nice looking PT. Though, if I can't get the James I may just go for a custom EP, or even a 300 series Hammond.

Thanks for all the tube suggestions too. The PS is a RCRCLC followed by a regulator. I can increase the resistors a little, too.
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Old 30th November 2006, 12:49 PM   #8
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Wow, that's nice looking. Your OPTs are beautiful.

The 5R4 is a bigger tube than the GZ34, but is very handsome, even inside. My version has a brown base -- would base color matter to you for a rectifier tube?

Can't wait to see the final project.

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Old 30th November 2006, 01:40 PM   #9
Sherman is offline Sherman  United States
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A 5U4-G drops a lot of volts (forget how many) but needs a 5V, 3A secondary.

I haven't dealt with these guys but maybe they can help locate a James PTX.

http://www.tubeaudiokits.com/index.htm
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