Thank you both, will check for dc later.
Was hoping it might be the case that amp is now running correctly and just drawing more idle current!

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This is the bulb previously.
I did check all of the new solder joints with a mm for continuity to other components.

With the new op amp in U1  the amp seems to be drawing more current through the 100w bulb. Not a huge amount, but the bulb is glowing slightly more. This is with the speaker still disconnected. What is a sensible way to proceed next? Does this suggest power amp diodes or q7 and 8 breaking down under load?
Should I connect the speaker at this stage? I would prefer not to blow the entire power amp again You cannot view this attachment.

Hi all,
I have finally got the amp out to work on again.I have installed an ic socket as suggested by Joe. Unfortunately the solder pad for pin 8 has lifted. Am I right in thinking this is not a problem as it is not on diagram?

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Thanks, will do. I do have an Mc1436 in my parts box from a supplier that I have bought good components from in the past. Can I test it in any way to check if it would be suitable?

Thanks,

Tp16 (U1 pin 7) and Tp17 (U1 pin 4) give the expected voltages of +25.7 vdc and -25.7 vdc.
 
Could the U1 still be causing problems?

Hello Phil,
Here are some pics of the wiring from the Transformer and power inlet area of the circuit.

The dodgy(!) looking joints on the board have since been reworked and checked with a mm.

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Thanks for the help,
Jumping the node at cp4 to chassis ground produces same buzz.  With neg lead of c53 shorted to chassis getting same buzz. I double checked Enzo's suggestion of shorting q7 at r59 but still buzzing.
I just plugged guitar in to check signal is passing through amp to speaker. Input 1 produces very distorted sound on clean channel. Input 2 is less distorted.

Clip of the sound attached...

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Checking grounding of some of the electrolytics-I am getting 757 ohm resistance to chassis  on pos lead of c53.

Thanks g1,
Have just checked r4 and r5 with multimeter and the grounding seems good and as expected.

Cp4 24.13ohms

Cp2 24.24ohms

I am reading around 24ohms resistance from cp4 to chassis ground.

Hello, does anyone have ideas about how I should proceed next? Is getting hold of a scope the best option?

Tp16 and Tp17 give the expected voltages of +25.7 vdc and -25.7 vdc.

Thanks Phil,
Continuity between earth pin and chassis is good and I have tried plugging into different plug sockets with same result.