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matt's basement
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Post subject: heathkit aa-15 replacement parts questions Posted: Jul Wed 25, 2018 2:25 am |
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Joined: Mar Mon 05, 2012 6:35 am Posts: 391 Location: Chicagoland, 60194
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Greg Dan
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Post subject: Re: heathkit aa-15 replacement parts questions Posted: Jul Fri 27, 2018 2:10 am |
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Joined: Jan Thu 01, 1970 1:00 am Posts: 1189
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Don't really have much to offer, but...
The AR-15 receiver probably contains the AA-15 amp, if you know what I mean. The only online paperwork for my AR-15, that I can find, is a schematic... so you probably already have better paperwork. But the AR-15 was / is pretty popular, so a search for it might bring up some relevant related info / tips for your AA-15. Also, there might be some online group that specializes in Heathkit audio gear. Best of luck.
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matt's basement
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Post subject: Re: heathkit aa-15 replacement parts questions Posted: Jul Fri 27, 2018 4:51 am |
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Joined: Mar Mon 05, 2012 6:35 am Posts: 391 Location: Chicagoland, 60194
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Greg Dan wrote: Don't really have much to offer, but...
The AR-15 receiver probably contains the AA-15 amp, if you know what I mean. The only online paperwork for my AR-15, that I can find, is a schematic... so you probably already have better paperwork. But the AR-15 was / is pretty popular, so a search for it might bring up some relevant related info / tips for your AA-15. Also, there might be some online group that specializes in Heathkit audio gear. Best of luck. Thanks and yes the AR-15 receiver contains the same AA-15 amp. The AA-15 came out in '68 and I believe the AR-15 came out a year earlier. My manual is dated 12-19-69 so I assume there must have been either changes to the manual or possibly a circuit modification. I have virtually zero experience with solid state amps so I decided it was best for me to stick with the original 40409/40410 drivers and 40411 output transistors although I have since found MJE253/243 drivers probably would have worked fine, been more robust, and saved me $10 or so. And I could have saved another $10 using MJ802G for the output transistors. If I ever acquire another one I'll have learned a little hopefully. There is a guy on youtube with a video about what a pain it was to restore an AR-15 for a young customer. He shows it hooked up to a THD meter and his results aren't near what Heathkit published when new. Hopefully I can do better. He was doing it as a business and I'm doing it mostly for fun. I also have the matching AJ-15 FM tuner and it came with a nice set of Dynaco A25 speakers. Probably been together since new and maybe a one-owner. Cosmetically they are very nice with hardly a scratch on the wooden cabinets. They have the cool Black Magic front panels and should light up nicely when finished. Matt
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Barry H Bennett
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Post subject: Re: heathkit aa-15 replacement parts questions Posted: Jul Mon 30, 2018 1:56 pm |
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Joined: Nov Wed 30, 2016 7:35 pm Posts: 5363 Location: Sunbury, Ohio 43074
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I had an AR-15. Foolishly got rid of it when in my late teens. It blew several of these transistors, and of course the outputs and the resistors along with them, until Heathkit finally decided it was the output sockets. That finally fixed it, and the AR-15 blew out my windows for years to follow with my AR2AX speakers.
At any rate, the transistors attached to the heat sink can be substituted by a similar spec transistor with a separate heat sink... these were just welded to the sink at the factory and sold that way, eliminating one step in assembling units such as this. If you cannot find these exactly, just match up the specs with a replacement, and t hen find a heat sink that can dissapate the same amount of power. THAT may be the trick .... this package transistor might give you a challenge to find an aftermarket heat sink that will be sufficient. Hence the welded assembly you've got. I suppose you could always use a lesser heat sink and add a fan, but that might bring other issues........ thermal drift being one, not good in a push-pull arrangement
happy hunting
_________________ Preserving the hist. of electronics, one boat anchor at a time! :) https://www.bbtvtestequipment.com
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matt's basement
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Post subject: Re: heathkit aa-15 replacement parts questions Posted: Jul Tue 31, 2018 9:29 pm |
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Joined: Mar Mon 05, 2012 6:35 am Posts: 391 Location: Chicagoland, 60194
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Barry H Bennett wrote: I had an AR-15. Foolishly got rid of it when in my late teens. It blew several of these transistors, and of course the outputs and the resistors along with them, until Heathkit finally decided it was the output sockets. That finally fixed it, and the AR-15 blew out my windows for years to follow with my AR2AX speakers.
At any rate, the transistors attached to the heat sink can be substituted by a similar spec transistor with a separate heat sink... these were just welded to the sink at the factory and sold that way, eliminating one step in assembling units such as this. If you cannot find these exactly, just match up the specs with a replacement, and t hen find a heat sink that can dissapate the same amount of power. THAT may be the trick .... this package transistor might give you a challenge to find an aftermarket heat sink that will be sufficient. Hence the welded assembly you've got. I suppose you could always use a lesser heat sink and add a fan, but that might bring other issues........ thermal drift being one, not good in a push-pull arrangement
happy hunting Output sockets....hadn't considered that. Thanks for bringing it up. I'll replace them. I would suspect kit builders sometimes messed up the mica insulators and thermal paste. Actually my set appears to have been meticulously assembled. The manual has the guys name in it so I googled him and discovered he was/is a Bacteriologist Phd at U of Wis. Great assembly or not, after 50 years new mica and paste would certainly be in order. On that subject, I've been looking around and discovered Bergquist Sil-pads (same as NTE Thermo-pads). There is also a guy selling ceramic insulators. Probably isn't any advantage from mica, but since I've come this far and have already spent way more than I'll ever get back I ordered a few of each to play with.
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