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advise needed for an Heathkit AA100

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huggygood

huggygood

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Joined 2011
#1
I have the opportunity to buy a Heathkit AA100, BUT, the person who sells it paid too much.
So far, no problem, BUT, I fell in love with this amp, I find it super beautiful, BUT it is entirely original, I mean that it is a survivor and must be rebuilt completely what represents a lot of time and even more money.
my question is: this amp is worth it to be saved at a price of gold ?
because the beauty of the device is one thing, but how it works is another.
the only things to keep are:
Output transofrmers
the power transformer
the chassis
the 4 7591 Groove tube
1 12ax7
2 7199
and both PCBs

what is to throw:
all the other tubes
all tube sockets
the GZ34
all the chemical capacitors
all the link capacitors
I do not know the state of:
potentiometers (all)
rotary switches
 
#3
I wouldn't necessarily just start replacing things like tube sockets. It's entirely possible that the sockets have seen minimal wear over the years, especially if post of the tubes are originals. Do you really want to risk lifting traces on the board to replace a perfectly good octal socket?

Start by doing the obvious work such as:
New power supply caps
New diode to replace the selenium rectifier
New coupling caps
A thorough cleaning of the pots and chassis

Then get the amp and running and check DC voltages and have a listen.
 
#4
I would start with using it "as-is". Beginning with full dismantling is a quite safe method of destuction. A sensitive

replacement of what neeeds to replace is a better and cheaper solution. power tubes might need replacement, the other are considered good unless proven wrong. ( groove tubes are not original, they have been replaced during it's lifetime)
 
#5
A few years ago someone in the U.S. documented their rebuild of an AA-100, it might be on Audiokarma. Search around. In essence they replaced virtually all of the capacitors, and all out of spec resistors. The biggest circuit change was making individual bias adjustments for each 7591. A 10 ohm resistor was inserted between each 7591 cathode and ground to measure the bias current. As well the 470K bias feed resistors to the grids of each 7591 were reduced to 220K.
I was given an AA-100 about 10 years ago and just "harvested" the tubes and transformers then scrapped the rest. I might use the "iron" to make a 6L6 power amp.
Good luck! Steve
 
#7
in fact, things are moving in the right direction. it is not impossible that I exchange it against my Yaqin mc5881 and there, it becomes interesting. I'm starting to know about the old tube amp renovation and I love it, but the basic problem was the "prohibitive" selling price for an amp that must be completely renovated. now that this deal is feasible without me sort of money out of my pocket, it's much simpler, I just have to dig into my stock of parts and buy the rest. and in any case, I will not have dismounted it without listening to it after a minimum of restoration and control. the cool thing is that it has a power supply 220v, it will change me, all my other amps in 117v: D I will take pictures when (if) the deal is done on the other hand, I do not know the 7591 groove Tube, I only use Tungsol and JJ and EH for the 7868
 
#12
An unwritten rule in the US Navy:

When a kit of parts and instructions comes in to modify a piece of electronic gear, be sure to check out the gear and confirm that it is working properly. Then . . . perform the modification.

Just a word of wisdom, that sometimes works.
 
#13
I had one I bought used and ran for a couple of years until I found a better replacement. Biggest problem I had was the traces around the output tubes. The area under the tubes was burnt and the traces lifting off. Everything else was doable but the board kept degrading around the output tubes and occasionally they would red plate. I'd read about the mods for the bias circuit but by then it didn't seem worth the effort. With the metal cabinet on it ran really hot.

If there were replacement boards available then I might of kept it around for fun. It was kind of cool looking.
 
#15
yes,I never do mods until the device works perfectly in its original state. I read a lot before doing anything. I come from a world (the restoration of collection vehicles) where we do nothing without reason and without having documented. It's been a long time since I fell in love with an amp without listening to it. I think that passion can not be explained.

@ 6A3SUMMER
I still want to thank you for the time you helped me and gave me the right information for my Xam Mark IV. you knew how to give me the right bases and they serve me every day now. this morning again, I listened to my Xam and what a joy this amp. so here it is, virtual beer for you 🙂

end of story for the moment. the guy wants to try to sell him the price he bought ... 750 € I did not try to discuss. on the other hand, I made an offer for another which is in Europe, partly restored and for half the price
 
#16
750 E??? that is quite expensive for an average sounding amp when rebuilt. The appearance of this amp is very unique and if you like that type of looks i suggest you try an obtain the Heathkit AA151. It is similar in appearance but is hardwired and uses el84 output tubes. If you bypass the preamp stage that amp sounds really good.
 
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