B+ too high. Loud hum, low output.

[shepdog]

So Ive just finished building up a 6L6 push-pull poweramp and before putting tubes in, the B+ measured before the 360ohm resistor was a around 630v. i figured this would drop once I got the tubes in. With the tubes in, and the bias voltage right around -35v, I took it off standby. It starts out quiet and as it stays on it begins to hum and crackle. Turning the Pod up to the point where I should be going deaf, I can just barely hear it. I'm not sure where I should start with diagnosing this. There are a number of errors in the schematic I have attached and I believe that I have sorted out the ones that are contained in the section of the amp that I've built. Hopefully its just a diode in the bias section that is reversed or something.

Thanks

[img1600]http://oi51.tinypic.com/wisnif.jpg[/img]

[ToneMerc]

To help aid in troubleshooting, it would be nice to see a schematic of what you actually built.

TM

[shepdog]

Do you mean the part of the amp, or is the image not showing up at all? I built from the effects return and on. It starts on the far left of the schematic.

[ToneMerc]

Do you mean the part of the amp, or is the image not showing up at all? I built from the effects return and on. It starts on the far left of the schematic.

The image shows up, but I guess i'm confused. You said you built just the power amp section. That image has the full schematic. I want you to verify exactly what you built. "I built from the effects return and on.", is not telling me much.

Crop out all the parts that are not in what you built. Good troubleshooting starts with accurate, as built documentation.

TM

[shepdog]

Sorry about that. Messing with it some more, I found that after replacing the 47v zener diode in the bais supply, the bias voltage went from about negative 40v to 50v. Seems to have gotten the plate down to about 550v but thats still 100v higher than the schematic shows.

[img:823:949]http://i51.tinypic.com/qx2p10.jpg[/img]

[shepdog]

Double post

[Jana]

Where is the ground connection on the full wave bridge? You don't have any reference to ground for the HT supply.

If you had 630 volts to the plates and only -35 volts bias the 6L6's probably red plated very fast and turned to toast.

[shepdog]

I caught that error in the schematic along with a few other obvious ones like the half of the low voltage rectifier being grounded and the polarity of caps in the bias supply. The tubes should be fine as I was always very quick to flip off the standby switch. They weren't on long enough to red plate.

[Firestorm]

What are the voltage ratings of your PT?

[shepdog]

I wish I knew these things but there are no markings on the PT or OT. Assuming that they haven't been damaged somehow they should work fine as they came stock in this amp.

[shepdog]

I don't think this would have any effect on the voltage being high but I did use 22uf 450s in place of the 100uf 450s. Would not having the load of the 12ax7 or the resistor and zener that went along with it cause the B+ to be higher?