6V6 Musical Machine Power Supply Problems - diyAudio
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Old 29th August 2013, 04:51 PM   #1
kcrow11 is offline kcrow11  United States
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Default 6V6 Musical Machine Power Supply Problems

Hello everyone...I'm in need of some help so I'm posting here for the first time. I recently completed building Poindexter's 2006 6V6 Musical Machine. When I powered up the heaters the tubes lit up and began warming. After the tubes warmed up I flipped the power switch and the fuse instantly blew (using a 2A slo-blo). I have now rebuilt the amplifier 6 times. I finally discovered what is causing the fuse to blow (I blew 12 fuses fuses and 2 Caps before tracking down this problem). The problem is in the Main Power Supply Circuit, it is occuring on the two 33uf/450v Capacitors wired in series. Attached is the schematic with the location of the problem circled. I've tried relentlessly to contact Poindexter at every email address I can find....all are no longer working, AudioTropic's website is no longer valid, and I've read Poinzie's DIY Audio Pages completely through many times...I can still not find an answer to my problem. I'm hoping someone can shed light on this situation. The HV Iron used is the Hammond Transformer named in the schematic (167G120) it is actually a 120V CT. I'm guessing the CT connects to ground as with the Filament Transformer....but the HV Transformer's CT is missing from the Schematic. Do I leave it unconnected??? That wouldn't produce the full 120Vac though.

I really need to know why this circuit is overloading and blowing a fuse when the second lead from the transformer connects to in between these two capacitors. The Cap's get extremely hot...I actually had two 33uf/400v Caps blow up before the fuse blew...so I've been using 450v Caps now and have not had that problem. Please, someone who is more experienced that I....could you shed some light on why this could occur? Am I doing something wrong somewhere else that is causing this? All the other circuits test and work great when powered up (I built and tested all separately after the first build resulted in a no go). I'm getting frustrated and now searching for different Voltage Doubler circuits that I can build with this transformer....I don't have the funds in this project at the moment to buy a different transformer so I NEED to make this one work for the time being. Any suggestions, ideas, or remarks will be greatly appreciated! Thank you everyone in advanced for you time and help!
- Kelly

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Old 29th August 2013, 05:06 PM   #2
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First: in place of blown unnecessarily fuses, use a serial lamp (incandescent one) in place of the fuse so any overload will be easily seen by the light of the lamp. The lamp about the same power of the DUT (device under test).

Second, try a NTC in series to the trafo's secondary, may be the first charge pulse will be causing the headache.
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Old 29th August 2013, 05:11 PM   #3
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Bad diodes possibly. Make sure that the electrolytic caps and the diodes aren't installed backwards. The CT on 120 volt winding should NOT be connected to anything. This is a simple voltage doubler circuit.
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Old 29th August 2013, 05:25 PM   #4
eyoung is offline eyoung  United States
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I had a look at Ponzies schematic ... you mentioned a CT on HV secondary DO NOT set to ground ,tie them together and insulate ...

I am interested in a Voltage doubler for a guitar amp I'm collecting parts for right now. There are several schematics for voltage doublers in the forum just seach using the seach button rt hand end of tool bar.

Regards, Elwood
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Old 29th August 2013, 05:51 PM   #5
kcrow11 is offline kcrow11  United States
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Thanks everyone for the input. I do not have the CT connected to anything so that's good (check). I've changed the diodes each time I rebuilt this circuit, however I have not changed the type of diode. I am currently using the UF1007s, should I try a different type such as UF4007?? I had not considered the diodes bc they are working in the other circuits. I checked the Caps polarity....I've got them wired just as shown in the schematic...so that's correct (check). I've even used different caps thinking that was the problem.

So, I've rebuilt the circuit and tested it by building it one component at a time, powering on, testing with volt meter for proper voltage, power off and repeat. As soon as I connect two 33uf/450v Polarized Electrolytic Capacitors in series as shown, BOOM...Capacitors overheat, fuse blows. How can I rule out a bad transformer? With nothing connected, the transformer is giving correct voltages and seems to be operating correctly. Any additional thoughts??
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Old 29th August 2013, 06:11 PM   #6
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The choke and the 120 F are OK?. I insist on using a lamp in series to the primary of the transformer.
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Last edited by Osvaldo de Banfield; 29th August 2013 at 06:26 PM.
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Old 29th August 2013, 06:38 PM   #7
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Are you SURE that the diodes aren't installed backwards?
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Old 29th August 2013, 06:42 PM   #8
kcrow11 is offline kcrow11  United States
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Frank,

To be honest, I am not sure of that as this is the first project I've ever done that used diodes. I read that the white stripe around the base of the diode denotes the negative side. Based on this info, this is how I have connected them all. Before I go turning the diodes around, Ill wait to for your reply. It would e really nice if its something this dumb (and would not surprise me either). So, which end of the diode has the white stripe around the base, negative or positive?
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Old 29th August 2013, 06:55 PM   #9
kcrow11 is offline kcrow11  United States
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Quote:
Originally Posted by Frank Berry View Post
Are you SURE that the diodes aren't installed backwards?
Alright.....I feel dumb now. Thanks Frank! You're the man for pointing out diode polarity. i honestly had not thought about the diodes at all. i just kept connecting new diodes each time I'd wire the circuit and I connected them the same way (the wrong way). One of the diodes was backwards. This has solved my problem. On to finish building this amp! I really appreciate everyone's help, time and input. If only I had posted this a couple days ago...could have saved me all the troubles....thanks again.
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Old 29th August 2013, 07:03 PM   #10
Minion is offline Minion  Canada
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Quote:
Originally Posted by kcrow11 View Post
Frank,

To be honest, I am not sure of that as this is the first project I've ever done that used diodes. I read that the white stripe around the base of the diode denotes the negative side. Based on this info, this is how I have connected them all. Before I go turning the diodes around, Ill wait to for your reply. It would e really nice if its something this dumb (and would not surprise me either). So, which end of the diode has the white stripe around the base, negative or positive?
The stripe on a diode denotes the cathode and the other end is the anode , when used as a rectifier the Positive DC will come off of the cathode or the end with the stripe ..... In the Diode symbol the cathode is the end with the line ....
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