Marshall 1970 JMP 50W 1986.

[AS74]

A friends amp. Any advice on routine type maintenance please? I figure to change electo's, filter caps. Do the .22's across the rectifier need changing?

The 8k2's to the choke look toast!

Thanks.

[TigerAmps]

I would suggest an up front decision:
Keep it original as possible (for collectors value) OR functional and reliable (replace key components and parts that have drifted).

If the former, don't change anything unless necessary.

If the latter, the as follows:
Check all the resistors (especially the plate resistors on the 12AX7's) for drift and replace as needed.
Check all the non-polarized caps and replace as needed (most likely they will be OK).
Replace all the polarized caps (the ones with +/-); especially the bias caps (8uF/150V)/
Definitely replace the two resistors that look burned (10K/1W) and when installing new ones, keep them off the turret board a little.
Spray the pots with contact cleaner
If you have the "push in" style voltage and ohm selectors, I would clean them as well.
I can't see from the pictures what you have.

[AS74]

Thanks TigerAmps.



Are the Wima caps original? Haven't seen them in any photo's on the net..

[olddawg]

Spray the pots with contact cleaner
If you have the "push in" style voltage and ohm selectors, I would clean them as well.
I can't see from the pictures what you have.

Be carful with anything called "contact cleaner", especially the old "tuner wash" type. It can very easily seize up pots and melt some plastics. Use a contact restorer/lubricant like Caig Deoxit.

[AS74]

I have Deoxit. Cheers.