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Hi,
i was dumping off some garbage the other day and on top of the metal pile was a heathkit AA-32 tube hi fi. I checked it over and it looks visually like it was built and used but put into storage a ling time ago and then thrown out last saturday.
I would like to get it working but i know better than to plug it in yet......whats a good plan. I would like to give it a good clean, check all the transformers for continuity and shorts and replace any all the caps that would be way to old now to even trust for 1 second ( all the caps are the originals).
I dont have the specs or schematics for it yet but does this sound like some good first steps to not blowing up something i cant replace or am i missing anything?
I dont have a variac but i have a light bulb current limiter that i have used on tube equipment but that stuff was working when i got it and not an unknown quantity.
Any suggestions on the safest way to proceed is appreciated.
Thx
Follow Ups:
While not of good quality, a schematic can be found via the link provided below.
Jim McShane gave you the big hints. Switch to 6BQ5/EL84 O/P tubes and eliminate the tone controls. Build a proper DC heater supply for the phono section heaters that's energized by an additional filament trafo. The 600 mA. saved by doing that provide, and then some, for the heater current demands of 6BQ5s vis a vis 6GW8s If you use MOSFETs in the "concertina" phase splitter role, no additional socket(s) need be added to the chassis. ;> ) Use 12AX7s where 6EU7s were OEM.
Rebuild the B+ PSU along the lines shown in the uploaded "El Cheapo" schematic. That's the right way to build a voltage doubler setup. While the Heath power trafo probably can't tolerate 820 μF. 'lytics in the doubler stack, it almost certainly can tolerate 150 μF. parts there. Reduce ripple and improve regulation.
The OEM SS diodes are NOISY. Replace them with UF4007s.
Eli D.
Thats funny. A while back I bought an unopened AA-32 Kit. It is still in that state.
The original text was removed since the post can't be deleted.
Edits: 08/14/12
Can't the OP just build & run the thing, as is? With a proper setup the unit could last a long time. Then, worry about adapting it to available tubes, when the original ones wear out.
One thing I would do, is concentrate on the electrolytic caps. Maybe, try a nice slow ramp-up (with a Variac) of the original ones (if they seem to have sufficient 'lytic fluid --- I've seen several succesful attempts, using this technique, on Ham Radio kits.
Or simply replace with new ones. I still like to slowly ramp up new caps, for wiring safety sake. And good Karma. FWIW.
Good luck with the kit!
sounds like it didnt see much use.....
There was a parade? I missed it.
Jim,
The 6GW8 data sheet shows the triode section as being pretty much the same as that found in 12AX7s. The power pentode seems to resemble a hobbled 6BQ5. The OP rates (IMO) to get away with 6V6 class tubes operated conservatively.
Does the idea of using the OEM filament winding to energize a proper DC supply for the small signal tube heaters and the installation of a 12.6 VAC filament trafo to feed 12AB5 "finals" appeal to you? The "real estate" to add 2X Noval sockets, for power section small signal tubes, would be easier to find than that needed for 4X Octal sockets. If space is badly constrained, a single Noval socket could be added to accommodate the voltage amplifiers of each channel and MOSFETs used as the "concertina" phase splitters.
Eli D.
When you first start it up, place a 60 watt bulb in series with 120 VAC line in. If a short occurs, the bulb will shine bright & protect the amp internal components. Like Eli stated, first order of business is replacing all electrolytic capacitors. I do not trust any electrolytic cap over 20 years old.
ALL electrolytic capacitors require replacement. They literally dry out over time.
Eli D.
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