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Old 24th Jul 2019, 7:57 am   #2
snowman_al
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Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
Default Re: Heathkit MA-12 stereo pair of amplifiers

So late November another MA-12 comes up for auction. It looked a little 'scabby' in the pictures and obviously had seen some 'repairs', but did have some valves left.
I nearly did not bid thinking another would come along soon. (As it happens I have not seen another 'single' since then.) But in the end I did bid and had to pay slightly more than the first one went for.

I was rather disappointed when it did arrive.
It was not as well made as the first one and had seen several repairs. All the coupling caps had been replaced, as were the cathode bypass caps and one resistor. The large 60 + 250uF cap had gone, replaced with a 32uF dangler and 400uF can.
Worse though was the general rusty state that had not been evident from its pictures. Only one thing to do, strip it and rebuild it.
So I set about cleaning the chassis, treating the rust spots, cleaning or replacing the rusty hardware and checking the components.

Then I discovered why this one had stopped working, the output transformer was high resistance on one primary winding.

First 3 pictures are as it arrived. 4th is chassis stripped and 5th is cosmetic re-assembly (new valve holders, screw heads polished, coax socket replaced, etc.
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