what is causing variac like distortion?

[andrew]

I converted a working Rocket style with two EL84s to a two 6v6 version. However I am getting very low volume and no clean at all but I do get a saturated variac- like smooth distortion only. There is a hum that goes away when I touch the chassis. I disconnected the PI feed and still get a distorted low volume sound when I touch the feed wire. I'm getting the ballpark voltages and no readings look out of the ordinary. I get 3v on the heater connections. I swapped tubes and even the OT with no change at all. I've never experienced a bad filter cap but is this a symptom? Thanks for any help- I could use some sleep.

[dave g]

Do you have multiple speaker jacks, and are they the shorting type? Because if you've connected the shorting lug to ground, even if you plug in one speaker cable the output is still grounded and you will get something very similar to what you described.

That's the quick and easy fix. If that's not the problem, I would check all your supply voltages and look for the nail that sticks out.

[Cliff Schecht]

Sounds to me like you have a miswired center tapped heater winding. That would explain why all of your voltages are normal except for your heaters being half of what they should be. What PT are you using and what color wires do you have going to the heaters and to ground?

[Structo]

You have to measure the heaters with your DVM set to AC volts, then measure across the two heater wires, otherwise you are only measuring half of the circuit.

[andrew]

Thanks all, the speaker wiring is correct and I checked the heater ground lug also. I forgot to mention that when I changed the EL84s over to 6v6s I also removed the tube rectifier and used diodes. I had one on one leg and one on the other leg joining at the standby switch. The PT made noise and blew a fuse. I put an additional diode on each leg and this time the fuse did not blow. I may change it back to tube rectified and see what happens. Thanks for the replies.

[Structo]

Be sure to check your preamp cathodes and make sure they are grounded well.
I had an issue where my second cathode was not grounded properly and the amp sounded like a fuzz tone with a dying battery, sputtering, no volume.

[andrew]

I win tonight's prize. Oldtimers has officially set in: I had the screen supply going to pin 6. Thanks for the replies though!

[Structo]

It's the simple things!