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Old 5th Feb 2023, 10:05 pm   #1
TheMightyMadman
Triode
 
Join Date: Aug 2022
Location: Stockton-on-Tees, Cleveland, UK.
Posts: 39
Default Help Needed - Armstrong 626 Tuner Amplifier

Hi all,

I'm repairing/restoring a lovely Armstrong 626 tuner amplifier for a friend of mine - apparently, the volume control was scratchy and it smelled like burning during operation.

The controls and switches seem to be working well following a good clean out with contact cleaner - I've removed the mains filter capacitor (fitted to early units) which seems to have been the cause of the burning smell - I've fitted new channel fuse holders, as the originals had cracked - I've also replaced the three large blue Erie capacitors, which were bulging and had developed ESR.

After testing, it seems that the right channel doesn't work, on either speaker output (1 and 2). I checked the right channel fuse, and it was blown (I think it was like this when I received the unit); I replaced it (2.5A fast-blow) in case it had popped due to a user error (i.e. shorting the speaker output), and it didn't blow - I now seemed to be getting an extremely low output signal on the right channel (barely audible at max right balance and max volume), and one of the output transistors was getting extremely hot.

One of the audio transistors was testing badly in-circuit, but out of circuit the transistor seemed OK, and the problem seemed to be on the driver board itself. Two of the transistors on the driver board had shorted (see picture below) - one is marked "I6506 EV RCA 3G", the other "I6505 EC RCA 3H".

The parts test bad out-of-circuit; with them removed, the circuit is no longer shorted where they were, so I don't think there are other issues.

Does anyone know whether these can be directly replaced with a modern equivalent? If so, what are the part numbers, please?

Many thanks,

Adam

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