Heathkit AR-1500 with Thermal Runaway

[JD Harvey]

Maybe I could add the parts circled in red to the foil side of the board.

Last night I said screw it... I'll just replace every resistor with a 1%. Once pulling them out of circuit to test, why not replace them after subjecting the inferior parts to heat. Also, I was thinking..... The old parts have been heat cycled so many times, that can't be good. The board has been nearly fully rebuilt at this point, may as well keep going. If this doesn't work I'll explore adding the extra parts to the foil side.

I've completely rebuilt a Marantz 2245. It had the wiring hacked on behind the controls by technician Hackworth. He really f'd it up and it made no sense what he was trying to accomplish. With all of the documentation available online, I brought it back to pristine operational condition. The amplifier boards are light years beyond the AR-1500.

When I started the recap on the AR-1500 I thought how simple and it works.... Haha! Heathkit should've made an AR-1500 to AR-1500A output amplifier board upgrade kit. It would've only been 2 boards and a few parts. The AR-1500A has upgraded FM/Multiplex stuff so that could've been a different kit.

 

[JD Harvey]

mounting the diodes to the heat sink wouldn't be real difficult, just need to tap a hole if the isn't one and work out some sort of clamping arrangement. The idea is to have the diodes at a similar temperature to the transistors so the voltage drop across the diodes changes with the output transistors and keeps it overall more stable. Otherwise as the transistors get hotter, they will tend to conduct more current as the voltage drop across the junctions gets lower.

To make it adjustable maybe sub that 22 ohm for a 15 ohm plus a 25-50 ohm pot in series. That would give you a bias adjustment instead of just whatever it is.

Maybe..... .......Exploring one thing at a time so I don't get in more over my head than what I am currently.

Thank you for the suggestions and guidance.

 

[JD Harvey]

Still no joy. I give up and for me to declare that you know it was a real victory. I've invested literally hundreds of hours to this BS. Done. Stay clear of the Heathkit AR1500 is my recommend. Their are much higher quality, less problematic receivers out there. I'm going to reach out to a guy I know and see if he wants to deal with it.

 

[Tom B]

I have one of those AR-15 heathkit receivers. Amps are fine but AM and FM NG. Very difficult to get to the boards, as I assume was because the kit assembled in steps. To get to the tuner boards, you have to remove the dial cord which is a pain. I just put it on the side. If you want it for parts, come and get it in Bklyn NY., although Texas is a bit of a Trip.

 

[JD Harvey]

Replaced 98% of the parts on the board. Swapped the other few parts with the opposing channel. The board itself is the issue. A LOT of damn work to get to that conclusion. I'll stay clear of Heathkits solid state gear from now on. No thanks.

 

[Tom B]

I think they were fun for people without a lot of experience to build, but typically never sought after as a collectors item in my opinion. If you want a nice unit, Pioneer, Sansui, Kenwood, JVC, and Sherwood had some nice stuff in the 70's and 80's

 

[gadget73]

Want a real lazy solution? Yank the original power amp board out and refit it with some handy-dandy chip amp board that runs on compatible voltages. At that point you at least have something that works without it being only useful as a door stop.