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When I built the Tweed it worked perfectly. After a few shows the amp started to cut-off at high volumes.
i.e. the speaker farts (technical term) It seems it's being over driven.

Changed all the tubes and speaker to narrow down the problem. No difference.

Any suggestions were to start trouble shooting?

Duke recently had a Tweed issue he thought was an OT but found it was a solder joint.. Valve two pin two was shorting out.
Might want to check the tube socket pin soldering.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Yes I think your suggestion worked.
I just desoldered the shielding from the pot in case the shield wire was shorting out at pin 2 of the 12ax7
I will get my son to test it out on some of his rock songs and verify that it is truly fixed.
I will get back to you tomorrow Stephen. Really appreciate working with me on this problem late in the evening.

Hope it solves the problem, but you should redo the cable if it's confirmed.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

We tried the amp this morning. It still breaks up when we hit the guitar strings hard. When I was trying it I was playing a normal song.
It's starting to look like it might be the orange drop coupling capacitors possibly driving the tubes into saturation.
I'm going to also inject a signal and trace it with my oscilloscope .
Any other ideas Stephen ?

When i put a signal generator onto the amp it has a clean sound. But when I increase the signal strength to about 4 volts rms that's when the amp breaks up and the speaker starts to fart.
I know the output voltage of magnetic pick-ups varies between 100 mV rms to over 1 V rms for some of the higher output types. That's probably why it sounded great when i tried it.
A hard strum on all 6 guitar strings can also produce a larger output voltage swing, typically peak voltages of +/- 5 volts for single coil pick-ups and +/- 10 volt peaks on dual coil pick-ups.
That's the problem when my son really plays the strings hard the amp craps out.
He used the same guitar on all his previous shows with great sound then the amp started to malfunction.
Could the pick-ups be bad?

I don't think the pickups would be bad. You are using an AY7 in V1? You might dial the other channel volume up to reduce the OD but it doesn't solve the problem. You can also put a 470K resistor to pin7 of the PI to soften the OD. Could be the rectifier can keep up as to the volume level and thrashing! Did you have a spare to try?

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I suppose it could be power supply related too. Maybe a low filter cap?

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Yes I tried a new rectifier tube. No change.
I will try to put a 470K resistor to pin7 of the PI
What is PI?

Never mind obviously it's the phase inverter.
I'll try that

PI = Phase Inverter (12AX7 in this case).

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Is there any DC voltage on the grids of any of the tubes?

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

12ax7. Pin7 16 volts. Pin 2 0 volts
6v6. Pins 4. 307 volts. Pins 0 volts
12ay7 pin 2 0 volts. Pin 7 0 volts

Typo error 6v6 pin5. 0 volts

That looks fine.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Rather than repeat, here is some good info on locking distortion, which may be the problem,although I dont know why it would show up now. It suggests a change in something (guitar, technique, etc.) If you have .022 coupling caps, try those on the power tubes, or increase the grid resistor onthe power tubes from 1.5 to 5 or more.
Lower the input (i.e. less amp volume or lower vol on guitar.)

http://www.aikenamps.com/BlockingDistortion.html

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I haven't inserted the 470 ohm resistor yet. Later on tonight.
Do think putting some capacitors in parallel with the rectifier filters to increase the damping will help?

Not really, if it is blocking problem. You have to trim it at the front end. But give it a try but don't go too far as the 5Y3 can only handle so much capacitance.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Ok I'll give you feedback when I install the 470 ohm resistor

Added the 470 ohm resistor and it had no effect.