Heathkit AA-1800
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Condition | NEW |
Payment methods | |
Ships from | Mountain View, CA, 94043 |
Ships to | United States |
Package dimensions | 24.0" × 24.0" × 10.0" (55.0 lbs.) |
Shipping carrier | Local pickup only |
Shipping cost | N/A |
Original accessories | Manual |
Average | Research Pricing |
This amplifier came to our ham-radio repeater club from the estate of a former member. I've gone through it, corrected a few minor issues, and I believe it's ready to use. I just wish I needed it myself!
The AA-1800 was Heathkit's most powerful stereo amplifier, rated to deliver at least 250 watts/channel into 8 ohms with less than 0.025% THD (both channels driven). It's based on the Leach "SuperAmp" low-TIM design, with a fully-complementary double long-tailed-pair input differential amplifier and 8 bipolar power transistors in a series/parallel configuration. The amp also includes a sophisticated speaker-protection relay circuit, which senses the output voltage and disconnects the speaker terminals during turn-on, turn-off, and in case of any circuit faults. It's rack-mountable, and weighs in at 50 pounds!
I've renewed all of the internal fuses, cleaned the internal and external RCA jacks and plugs, cleaned the level and offset potentiometers, replaced the rather touchy bias-adjust potentiometers with precision multi-turn pots, and adjusted the bias and offset to factory specifications. I have not "recapped" it or made any changes to the circuit design, figuring that the new owner would probably prefer to make his/her own decisions about that sort of thing.
I burned it in at 10, 50, 100, and 150 watts/channel for anywhere from 5 to 30 minutes each, running into an 8-ohm dummy load. I didn't see any sign of clipping or other waveform distortion on my 'scope at any level. At 10 watts/channel, my old HP 331A read out at 0.03% and 0.025% distortion+noise (left and right channel respectively).
Cosmetically, it's in good shape for its age - a few scratches, and some chipped paint on the corners of the heatsinks.
Electrically... again, I think it's in good shape for its age. Its distortion performance seems to be better than I can measure reliably with my old HP meter. I haven't observed any misbehavior, and I know that the speaker-protection board does work correctly. When we received the amp, it went into "protect" mode as soon as it was turned on - one of the input-section fuses had opened (a common old-age fault with this model, as the 1/16-amp fuses are fragile). Replacing the fuse restored correct operation and it's worked fine since then. (I had to use 1/10-amp fuses here rather than 1/16-amp as these were all that was available locally).
It is, however, a 30-year-old amp. It may have problems I haven't found, or components that are suffering from age and will need replacement at some point. I'm selling it "strictly as is" for that reason. The Heathkit manual writes "Before using any audio amplifier - Heathkit or otherwise - you should contact the manufacturer of your speakers... to learn what type of speaker protection will be necessary to minimize the possibility of damage." I agree - this is a very powerful amplifier, and if mis-used might easily damage a speaker system!
The photos show the amp itself (several views), and the amp on my impromptu back-patio test-bench. The final picture shows the oscilloscope traces of the amp's output reproducing a 1 kHz sine wave at 35 volts RMS (100 volts peak-to-peak), delivering roughly 150 watts into 8 ohms. Yes, my dummy-load resistors got quite hot (hence the fan blowing on them!)
The amplifier and original owner's (assembly and test) manual are included in the sale. The other equipment shown is not included.
Local pickup only - it's so heavy that it'd be difficult to ship. Heathkit strictly required that the power transformer be removed from the chassis and shipped in a separate box, to avoid the risk of damaging the internal chassis frame due to a "Fragile Means Toss Across The Room" problem during shipping.
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