Another high voltage problem for a TOS

[m3moser]

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??

[VMS]

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

[tubenit]

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

[sluckey]

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.

[stingray_65]

  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

[m3moser]

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.

[tubenit]

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

[rzenc]

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

[sluckey]

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?

[Geezer]

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.

[tubenit]

m3moser,

Did you get the rectifier rewired?  Is this resolved yet?  Please update us.

With respect, Tubenit

[m3moser]

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.

[tubenit]

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