ao35 conversion

[davebolden44]

was wondering if i could get a little insight on my current problem. i have an ao35 unit that i converted to specs from the phoenix schematic with a cut control. issue is i have distorted sound if i bang on the guitar but a light touch bears no sound at all. all the voltages are within very good tolerance with the exception of the phase inverter cathodes which should measure 26 volts but i am getting a reading of just over six volts. i have gone through the wiring very thoroughly and checked values of component etc. however i feel i have peaked with my troubleshooting skills. rebias??? any insight in the matter would be appreciated, thanks
Dave

[xtian]

Sound when you hit hard makes me think floating grid. That is, forgotten grid reference. Make sure MV is properly grounded.

That's an oddball PI. Not familiar with that one.

[davebolden44]

pretty sure its a long tail pair just not quite as sophisticated
as a marshall with unbalanced plate load resistors and what not. i will check the grounds but i have a wire coming from the volume pot running strait to my ground buss. it sucks cause this is a prototype layout i am using and the space is super tight and i need to lift certain components to get to others in the power supply. i am pretty sure the voltage at point k is also 6 volts where it should be 15.6but i havent looked at it for a couple days as work has me busy at the moment. i will try to post some pics of this rats nest

[davebolden44]

[IMG576]http://i1033.photobucket.com/albums/a417/davebolden44/Mobile%20Uploads/20160825_173658_zpsd3a5tjwy.jpg[/img]

[IMG576]http://i1033.photobucket.com/albums/a417/davebolden44/Mobile%20Uploads/20160825_173735_zpsslus9azw.jpg[/img]

BTW, a weber cap can is a drop in replacement on an ao35 chassis if anybody cares or can use that information

[Malcolm Irving]

It seems to be a long-tail-pair, but with an unusual fixed-bias arrangement. The bias on both the 5751 triodes is given by the difference between the common voltage at the cathodes (supposed to be 26V) and the voltage at both grids which is supposed to be 22V (from point D). That’s -4V which seems a bit on the cold side.
What voltage do you get at point D?
What is/was the Phoenix project, by the way?

[davebolden44]

i will check that out and post a reply momentarily, i think that the phoenix schematic is just a rip off of the carmen ghia, but this version has an added cut control.

[davebolden44]

ok that was more than a moment, i will post it after work, my buddy came over and distracted me

[Stevem]

While you are in there that right hand terminal on the pilot lamp is really close to the PT bell, I would glue some card board there for now!

[Teleguy61]

Yes exactly Stevem, you have to insulate that pilot light when you build into the very small AO-35 chassis.
dave, the phase inverter voltage supply is complex and a tricky wiring chore in that little chassis. I'd suggest checking that carefully.
If you are getting 6 volts at the test point instead of the specified 26 something is not right.
Mine came out bang on 26, lucky for me.
Good luck.

[davebolden44]

ok I havent done the repair yet but i think malcolm hit it on the head i have 0 volts at point d. also with the fear of sounding hardheaded, i think its just the camera angle with the pilot light. its above the bell housing somewhat and i feel it stands no chance of coming in contact

[davebolden44]

UPDATE - point d was finding a path to ground via the mounting risers i used on the ot mounting screws. thanks to all for helping me find this. attenuated, this amp is awesome!