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oscillating 6550 set amp. long




Hey Guys,

I've been working on a set amp kit for the last 3 months. I have built several other kits and this is by far the toughest for me. I made the mistake after opening the boxes and going thru all the parts accepting it, knowing this looks like someone just thru together what they had on the shelf. I only say this so we can troubleshoot the amp better.

As of last week I had not gotten any sound out of the amp. This week I started messing with the heaters on the 6550's. They are ac heated. Per spec it has the lines from the power transformer high side go into a .68 ohm resister to pin 2 (7) of other 6550. Low side feeds pin 7 (2) with a wire going to ground. With the manual that was sent, originally the power tranning had four wires for the heaters, now the tranny only comes with two wires for the heaters.

When I hook up the heaters per spec, I get no sound out of the speakers. The 6550's don't heat up at all. If I hook up the heaters in series, one channel will give music and the other channel little music. If I turn it up all all the channel with little music will start to oscillate.

If I hook up the heater wires, high side feeding both .68 resisters and run them pin2 of one 6550, pin 7 the other 6550. opposite of the low side but I don't hook up the ground. I get music out of both channels but only for about 3 minutes. Its starts oscillating. Volume will not stop it and I have to turn the power off.





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Topic - oscillating 6550 set amp. long - frankford 14:00:10 03/04/12 (33)

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