[TheMightyMadman]

Originally Posted by PaulR

Those potentiometers certainly caused problems for me. I would replace them even if they appear ok at the moment.

Thank you I'll consider this.

Originally Posted by G6ONEDave

There are various Motorola MJ types on the CPC website. Such as MJ15016G and MJ15025G (PNP type) along with the NPN versions. These vary on voltage from 120vce to 140vce. they have 16amp and 20amp versions, so something there will probably do the job but be mindful about the changes in substrate changes over the years. There has been discussion about this for the 2N3055 on this site.

To bring up a list of stock on the CPC webpage enter in the search box 'pnp transistor' or 'npn transistor', this brings up all their stock types. You will then have to scroll down to the MJ types and check the data sheets to see if anything looks OK for your repair.

Good luck.

Dave

Thank you

Originally Posted by stuarth

To avoid the destruction of the new transistors because there were other faults, I used to wire a 270R 3W wirewound resistor in series with the DC supply to the power amp. If all was well, the amplifier worked normally at low volume with very little voltage drop across the 270R. If there was a remaining fault and the amp drew excessive current, the resistor would get very hot very quickly. With separate DC fuses for each power output stage, it is very easy to remove the fuse and tag the resistor across the fuseholder.

This trick is usually quick and easy to apply. I used radial leaded resistors with mini crock clips directly on the resistor leads, it was self supporting in mid air. Using these resistors, I never blew the replacement transistors, and I always noticed the hot resistor before it came to harm (dissipation would be over 3W on most amps).

Stuart

That's a good idea, thanks! I'll certainly consider doing this in future