Well, there are probably half a dozen posters where who know what I am talking about.

The Hill DX700 was born in the late 70s and in its day was a mighty beast of a power amp producing 625 + 625 watts RMS into 4 ohms. Mine is sick, producing a mighty DC thump from one channel at five second intervals. Other channel OK.

The problem appears to be the interstage transformer that goes between the 3020 chip that is used as a driver stage and the power stage. The 3020 is an audio Op-Amp that can produce up to 20 watts of audio. In the Hill it drives a 1:1:1 transformer that produces symmetrical drive for the output stage which is therefore close to class A.

Taking out fuse to input stage produced a thump-free situation - therefore fault was driver or earlier.

With 3020 in circuit, (and fuse to output stage removed) supply voltages to 3020 on the dud channel read -9 0 +9.

WIth 3020 out of circuit (and fuse to output stage removed) supply voltages to 3020 on the dud channel read -15 0 15 (which is I think as it should be and is as the other channel is).

Replacing the 3020s results in a pop and a destroyed 3020 (twice so far).

So it's probably a largely short circuited input winding on that transformer (if it was the output winding there would be much less drive to the output transistors).

Regrettably the PCB on which that 3020 is mounted has been done so many times in the past that that 3020 has to be connected with fly-leads, but I can live with that.

My usual repairman (he is good) is talking glumly about custom wound transformers at a price of rather too many beer tokens.

Anyone know of anyone with any of those transformers or any Hill DX700s going cheap for spares or repair?