Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: m3moser on August 22, 2010, 03:02:33 pm
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Rather than hijack the previous thread on this topic, I thought I would start my own. I have built the TOS but I am having a real issue with voltages. The schematic shows the use of a diode rectifier and I had a hammond P-T290DX on the shelf (325-0-325) that seemed perfect. Since I did nt have room for another tube, I decided to use a set of diodes for my rectifier just not in a socket mounted and more expensive version like the schematic. Should be no problem, right?
After the rectifier I am reading over 600 volts with a full tube load. I have to currently use a long string of dropping zener diodes to get my voltage down to near the schematic volts and alter my dropping string as well. But I cannot figure out why so high? Has anyone else encountered this before? My wall voltage runs a little high (about 127 volts) but I can't get my head around the voltage. Its almost 1.9X the input voltage? Can there be some other difference in a tube mounted diode rectifier as shown in the schematic??
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Hi,
is the center tap grounded? What type of rectifier are you using? Full Wave Bridge or Full Wave?
Here is Hammonds design guide for rectifier use:
http://www.hammondmfg.com/pdf/5c007.pdf (http://www.hammondmfg.com/pdf/5c007.pdf)
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325 X 1.4 (solid state rectifier) = 455v. You stated 325-0-325 correct?
How are you getting over 600v?
I am using a GZ34 in both my Tweed Overdrive Special and Carolina Overdrive Special. Or I can use a 5V4 with 5881's or 5Y3 with 6v6's.
325 x 1.3 GZ34 = 423v
325 x 1.2 5V4 = 390v
325 x 1.1 5Y3 = 357v
Make sure you have a fresh battery in your voltmeter and try reading it again & repost. A bad battery can create some very goofy readings.
With respect, Tubenit
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The only way to get 600VDC from a 325-0-325 PT is to connect a bridge rectifier to it and ignore the center tap. Replace the bridge with the conventional full wave circuit in the lower left corner of the pic Tubenit posted.
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After the rectifier I am reading over 600 volts with a full tube load.
Are you having other issues with the amp?
If it's under full load I assume you have sound correct?
It just reminds me of a situation I found myself in not all that long ago, There was indeed no load and what I was reading was the first capacitors loaded voltage.
Can you post a gut shot of your amp? especially near the power supply and your octal sockets?
Ray
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Hey Guys- the center tap is grounded. The rectifier is a full wave bridge (I'm using 4 diodes in two pairs each side). I am now wondering if I have a bad transformer? My battery in VOM is nice and new- still has that new battery smell. I don't usually measure my transformers before I install them as the unloaded voltages are not accurate, but maybe I have to start. Thanks for all the ideas.
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Before you chunk the PT ................
What do you get in VAC going into the solid state rectifier?
Does it measure 325-0-325 ?
With respect, Tubenit
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Replace the bridge with the conventional full wave circuit in the lower left corner of the pic Tubenit posted.
Hope this helps
Best Regards
Rzenc
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The rectifier is a full wave bridge (I'm using 4 diodes in two pairs each side).
Huh? I'm still confused. Is it a full wave bridge or is it a conventional full wave rectifier?
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The rectifier is a full wave bridge (I'm using 4 diodes in two pairs each side).
Huh? I'm still confused. Is it a full wave bridge or is it a conventional full wave rectifier?
Yes, if you indeed do have a full wave "bridge", then THAT is your problem.
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m3moser,
Did you get the rectifier rewired? Is this resolved yet? Please update us.
With respect, Tubenit
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Hey Guys- I am traveling this week so not in the shop. I have the exact rectifier as posted above with the grounded center tap. When I get back in the shop I will take the AC voltages both connected to the diodes and free of the diodes. I was lucky enough to have a 600V first capacitor downstream from the B+ or else I am sure it would have been some nasty smoke released from it.
More later in the week. Oh, the amp sounds a bit strange to be sure and I am not happy with this but need to start from basic voltages first.
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PLEASE measure the VAC voltages prior to the rectifier & post those when you get a chance.
We need to establish for sure what that is first before going any further in problem solving.
With respect, Tubenit