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Audio and Video Talk
The Vintage Audio Section
Split: Restoring Revox 1970s and 1980s amplifiers (and other components)
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<blockquote data-quote="Steerpike" data-source="post: 244181" data-attributes="member: 807"><p>The A722 has all its new transistors in, new capacitors, and only one blow-up when I first switched it on (The relay driver transistor: I cannot figure out what killed it, totally illogical. The replacement worked fine, and no odd voltages to be found. Only thing I can think of is a PCB trace crack, which I found elsewhere too in a different circuit area.)</p><p></p><p>It is singing very happily now! All that remains are new wood side panels.</p><p>The front panel was originally leaning, sinced the spacers that ought to go behind it at the top were missing - so it 'tilted' backwards. The correct front panel screws also make it look better. </p><p></p><p>Half the chassis screws hadn't been replaced either, so it had a sagging belly where the transformer made the bottom plate droop. All pretty and square now though.</p><p></p><p>At first I thought it wasn't working, because the DC offset is so small - I didn't think the circuit arrangement would give such a low DC offset without trimming - but there it is, 300uV on one side, 200uV on the other.</p><p></p><p>I'll get around to putting lamps in the pushbuttons, because they look so good when back-lit. Some circuitry will be needed, since the switches don't have contacts for lamps. Detection of the various circuit states will be needed to determine when the lamps must light.</p></blockquote><p></p>
[QUOTE="Steerpike, post: 244181, member: 807"] The A722 has all its new transistors in, new capacitors, and only one blow-up when I first switched it on (The relay driver transistor: I cannot figure out what killed it, totally illogical. The replacement worked fine, and no odd voltages to be found. Only thing I can think of is a PCB trace crack, which I found elsewhere too in a different circuit area.) It is singing very happily now! All that remains are new wood side panels. The front panel was originally leaning, sinced the spacers that ought to go behind it at the top were missing - so it 'tilted' backwards. The correct front panel screws also make it look better. Half the chassis screws hadn't been replaced either, so it had a sagging belly where the transformer made the bottom plate droop. All pretty and square now though. At first I thought it wasn't working, because the DC offset is so small - I didn't think the circuit arrangement would give such a low DC offset without trimming - but there it is, 300uV on one side, 200uV on the other. I'll get around to putting lamps in the pushbuttons, because they look so good when back-lit. Some circuitry will be needed, since the switches don't have contacts for lamps. Detection of the various circuit states will be needed to determine when the lamps must light. [/QUOTE]
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Audio and Video Talk
The Vintage Audio Section
Split: Restoring Revox 1970s and 1980s amplifiers (and other components)
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