Nice to hear from you my friend. Sounds like you done good with that AA-1800. Thanks for elaborating on the changes you made - it's good info for me. I had considered changing the input pots on my amp and had the parts on my wish list but decided against biting off more than I could chew since it was working fine except for a very slight hiss in the right channel. I bought the amp in roughly 2005 from a guy who had built it back in the day and personally recapped it circa 2002-2004. He was more of a tech than I am and even gave me all the old parts he replaced. I didn't notice the hiss until a few years later, and it is the reason I finally did the recap, which cured it. However after I got my system up and running I was perplexed to find a problem with my AP-1800 preamp. The right channel had reduced volume and slight distortion in the phono 1 circuit off and on. So I bought another recap kit from the same eBay source, recapped the unit and carefully cleaned every switch and pot with Deox. Everything sounds like new again and I'm very happy, so much so that I'm attaching a picture to show off a bit! I think you'll recognize the Heathkit components. The rack is Heathkit as well. Resting (unmounted) on top of the preamp is a 1990ish Yamaha "Natural Sound" CD player. The turntable is a Bang & Olufsen TX 2, also 1990ish. Peeking in on the right is my vintage Nakamichi LX-3 cassette deck circa mid-70s. Everything runs through a pair of JBL L112 speakers that my wife gave me as a wedding present back in '83 (she loves me for some reason).
Inherited this original owner set of HeathKit electronics. Includes a AA-1800, AP-1800, AD-1706, AD-1703, and AD-1701. Initially during testing, had sound thru both channels, but I think the right channel pot may have caused the 5A fuses to blow on the bottom right rear circuit board. After cleaning and testing the pots, I put new fuses in, and they both blew on power up without anything connected. For a kit amp it looks to be complicated to get to the top of the circuit board for a looksee. Any help would be appreciated before I make any mistakes looking for what I can't find. All the boards and components look fine without any obvious signs of burns or chars. Dad says the unit has never been touched internally since the 1982 service tag, and everything inside certainly looks that way. I have the ability to re-cap or do some basic testing, but I don't want to get caught up in any output transistor drama if it comes to that. I have a multimeter, capacitance tester, and transistor tester. I only have the manual for the pre-amp, and nothing else at this point. Any input would be appreciated to help me decide if this project is in my best interest.
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I know this is long silent thread, but these Heath AA1800 amps will outlast us all! I'm resurrecting mine after it was stored for a number of years. I have the original manual, schematics, build drawings and all my notes. I acquired the unit in 2004 from the original builder.
At that time I did a complete replacement of all the output transistors ((MJ15025 & MJ15025), performance matching them as well. Some of the original output transistors had been replaced for unknown reasons, so replacing them all with fresh, 25yr newer transistors seemed prudent. At that time I was in communications with one of the Heath technicians who worked on the AA1800. Lots of good info was passed along. In particular, he stated that the main design engineer was never happy with the 0.33 ohm, 5w emitter resistors for Q117, Q118, Q121,& Q122. He stated that the engineer wanted less resistance but still some small value, but at the time the .33 ohm was the lowest commercially available option. He indicated that they discussed just putting fuses for the emitter resistance, but sanity prevailed. Given that I was replacing all the output stage transistors, I ordered up 0.1ohm, 5w wire wound resistors to replace R138, R139, R144 & R145.
Presently, I am recapping the AA1600 using the refurb kit from HiFiAudio. Additionally, I'm replacing all of the 3300ohm CC resistors, R154, R155, R152 & R153 with 3300ohm, 1%, 3W, wire wound, along with R156 & R157, 10 ohm, 5W as these have proven to drift out of spec over the decades and they form the voltage divider for the +/-100 rails. Obviously, I will adjust the offset and bias once the various parts are replaced.
As the amp was working perfectly when it went into storage, I suspect it will once again exceed all expectations. FYI, that same Heath tech mentioned that they put his proof build of the AA1800 on the bi
