Anybody heard of a Harman-Kardon Procast 4015 amp?

[GordonW]

Got some unusual old amps...

Harman-Kardon Procast 4015... rated at 150 watts, transformer-coupled output (8 ohm, 25v and 70v outputs). Huge chassis (FIVE rack height, rack mount)! Can't verify, but if asked to speculate, I'd guess made between 1965 and 1970.

Looks to be built with the topology of a tube amp, only using solid-state devices... push-pull, through the transformer, all the transistors are NPN (three on one side, three on the other, each driving half of the center-tapped output winding). These may be one of the earliest examples of "tunnel cooled" heatsinks... there's a fan on the top of the unit, and the heatsinks draw air upwards from a vent in the bottom, through the heatsinks, and up through the fan on top. Uses 2N3773 output devices... which IIRC, are the same as the original Crown DC300 output devices...

These came out of Oak Ridge National Laboratory (yeah, I know, we need to scan them with a Geiger counter, probably )... but I haven't been able to find any info on them. They need rebuilding (the one that I hooked up, went dead-short and blew the fuse after being on for about 10 minutes, while being brought up on a variac), but there's some SERIOUS IRON here...

Regards,
Gordon.

[Ducatista47]

Haven't seen this one before, but...

The iron may be serious, but an all NPN design of that era would have been designed to a price rather than from a great engineering standpoint.

Early solid state designs' greatest accomplishment was avoiding immediate thermal runaway, not good sound. IMHO that is still the situation with transistor amps. That is, when they do avoid self destruction and DC or harmonics death for our fine speakers.

Solid state devices in power supplies, and MOS-FET outputs, are another matter. I am on board with those.

YMMV, Clark in Peoria