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Old 4th October 2013, 03:29 AM   #1
dmb5245 is offline dmb5245  United States
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Default Too much B+

I turned on my SSE and it was working great for about 10 minutes. Then my rectifier tube turned into a bug zapper and blew the fuse. I figured it was just a bad tube, so I switched over to solid state and everything continued to work fine. I figured I was safe, but then I checked my B+. 520V. Yikes. Then I checked the secondary of the PT and it read 420VAC. Yikes again. I don't know if those numbers hold true with tube rectification because it arcs and blows the fuse before it can be measured now. I'm using the Edcor XPRW033, which is rated at 380-0-380. I know that's a little higher than suggested, but the PT is clearly running hot. I don't think it's my meter either, since I'm reading 122VAC out of the wall as expected. Does anyone have any suggestions about how to fix this, short of replacing the PT? I really don't want to risk blowing the power supply caps - my fiancé would not be pleased. My thoughts:
1. lower the capacitance on C1 - currently 47uF
2. swap out the rectifier tube for something like a 5Z4 and not use the silicon
3. a resistor in series, but I don't think that's a good idea

I should also not that I do NOT have the diodes in D3 and D4 and have a CL90 in TR4. The diodes and a CL140 are on their way now, but that won't change the voltage, right?. Also, I'm using the Hammond 159Q (7H, 150mA, 100ohms) as my choke.

Sorry for the long post and thanks in advance
Dave
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Old 4th October 2013, 09:54 AM   #2
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Circuit please.
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Old 4th October 2013, 12:31 PM   #3
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I'm a novice so can't tell you much. Do you have jumpers in D3 & D4 ?
You should if you don't have the diodes in there.
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Old 4th October 2013, 02:17 PM   #4
dmb5245 is offline dmb5245  United States
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JonSnell, I assume you want a photo of the wiring? I won't be home for a few days, but I can take a photo when I get the chance. I think the wiring is all correct, it's just that the PT is putting out too much voltage.

Harry88, yes, I have jumpers in D3 and D4 until the diodes I ordered arrive.
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Old 4th October 2013, 03:29 PM   #5
FoMoCo is offline FoMoCo  United States
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Two things come to mind:
1) A bucking transformer on the primary. A regular filament transformer of 12V or so would be a good place to start.
2) Resistor is series with the rectifier. The problem here is that the voltage will change with load.
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Old 4th October 2013, 03:32 PM   #6
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If your secondary is really putting out 420V, that's the problem. Are you sure that's the case? That's over 10% higher than what it's spec'd at. Can you get Edcor to swap it?

The SSE runs the rectifier pretty hard with the recommended voltages already. Were you using a 5AR4? Stock values at C1, C2 (47uf, 120uf)? That looks like almost 700V on the rectifier tube in PSUD2. Yikes indeed.

Last edited by Sodacose; 4th October 2013 at 03:37 PM.
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Old 4th October 2013, 03:56 PM   #7
dmb5245 is offline dmb5245  United States
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Soda, I'm pretty sure that it's 420V. I'm measuring the VAC from the screw on the green connector terminal where the red PT secondary connects to ground and consistently getting 420VAC. The B+ is being measured similarly from the green connector terminal of the OPT red primary and it is consistent also. This is with a full load (all tubes in, music playing). I'm using stock values for C1, C2 and a JJ-5AR4.

Fomoco, you're a little over my head on the bucking transformer suggestion. Any suggested reading for me? Also, what size resistor do you think I'd need?
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Old 4th October 2013, 04:19 PM   #8
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Have you contacted Edcor about the transformer? Was it new?

I'm sure you're itching to get this working ASAP (now that you heard the sweet, sweet tunes), but I would be asking Edcor to swap the transformer if it were me. A 10% difference in what you paid for and what they delivered is pretty extreme here. A true 380V secondary would probably be fine without having to mutilate the otherwise simple design.

They seem like good folks from my experience and would probably want to make it right. Doesn't hurt to ask.


Edit: If you didn't already realize it, you're exceeding the rating on your C1 and C2 currently (assuming rated for 500V). Even if it's working on solid state, be careful.

Last edited by Sodacose; 4th October 2013 at 04:29 PM.
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Old 4th October 2013, 04:56 PM   #9
dmb5245 is offline dmb5245  United States
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Darn your sensible view of things! I was hoping there was an easy way out that didn't involve waiting on Edcor, but I had a feeling there wasn't. I just emailed them, so we'll see what they say. Either way, I'll probably get nailed on the shipping and will definitely remain tuneless for awhile . Thanks for the warning about running the caps too hard, but I pulled the plug as soon as my voltmeter gave me those nasty numbers. I'm actually impressed the FREDs and the output tubes didn't blow being hit that hard. Thanks for the help
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Old 4th October 2013, 05:03 PM   #10
FoMoCo is offline FoMoCo  United States
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Quote:
Originally Posted by dmb5245 View Post
Fomoco, you're a little over my head on the bucking transformer suggestion. Any suggested reading for me? Also, what size resistor do you think I'd need?
Rod Elliot has written a good article on using a bucking transformer.
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