Heathkit Amp & Preamp

Yes, it does sound like a contradiction but by low impedance I am saying very low loads, like 2 ohms. I no longer own the AA-1640 manual, but believe it was rated only at 8 ohm possibly 4 ohm, but not below that.

Heathkit often warned in their manual and amplifier construction documentation against having too many 'parallel' speaker connections to their amps thereby reducing the load much below rated values (i.e. 4/8 ohms) due to stability concerns. Perhaps they were just being conservative in their recommendations.
 
Heathkit often warned in their manual and amplifier construction documentation against having too many 'parallel' speaker connections to their amps thereby reducing the load much below rated values (i.e. 4/8 ohms) due to stability concerns. Perhaps they were just being conservative in their recommendations.
A lot of manufacturers do that. Usually has to do with UL testing.

But, it could also be that "high current" was a result of the marketing department and not the engineering department.
 
Pro Series Rack

Hi:
I have the whole series pro rack AJ 1600 , AP 1800 , AA 1800 and the AD 1701.
The most trouble I have had is with channels dropping out intermittently. After a lot of hair pulling and cuss'in and lots of other stuff , I found the in and out RCA jacks are ABSOLUTE CRAP.
The solution is to take the unit apart so that you can get at the jacks with a soldering iron. You will notice that the jacks are two piece , the solder tab is crimped to the shell . I take a soldering iron and flow a little solder into the joint. To do this heat up the jack so the solder flows when you touch the jack with the solder. A little goes a long way , don't short the jack , ask me how I know , just enough to make a good connection. This cured the problem.
On the pre there is not enough room to change jacks but on the tuner and the amps I will replace the jacks with something better.
Hope this helps
Ed
I know this is old but your advice to solder the rca inputs/outputs is extraordinary. My AP 1800 was dropping a channel several times over the years and I alwayS went after the pots and switches. No luck, a channel would drop again. Almost ready to buy a new preamp until I just happened to find your fix…seems to work now, let’s see how it goes going forward. THANKS VERY MUCH!