Hafler DH300 Monoblock forever?

You are correct, concerning the 2.2ohm resistor(R45/pn 133022). There was only one provided, in the kit. The DH-200 schematic shows that on the ground of the left input. Given the age of your amps(30yrs+), you might consider obtaining some new power supply filter caps. Though yours may still work; I promise you will notice a marked difference in performance, with new ones. ( http://www.digikey.com/product-detail/en/CGS103U075V3C/338-1244-ND/953292 )Happy listening!

Im going to show some of technical ignorance here, but are you referring to the big caps, 10,000 uF that are connected via the bridge rectifier? I think I can pick up a set from QA-Con , I think that's the supplier on eBay for about 50 bucks. They also sell full kits of all the smaller caps as well. What's the story I hear about "conditioning" amps that haven't been used for a long time with a variac or other type set-up? Thanks again! Off to radio shack to get some phono-kack bulkhead mounts to take out these headset jack type input jacks.

Yes- those are the ones. Be careful from whom you buy the caps. Believe it of not; aluminum electrolytic capacitors have a shelf-life. re: the variac- It's good to bring the voltage up slowly(and, "reform" them), when electrolytics haven't been powered for a long time. Some good info here: ( http://www.allegrosound.com/index21.html )

Wow, almost sorry I asked, now I can't plead ingnorance. Will have to see if I can locate someone with one to lend me. I have a plain vanilla DVM I use so I don't think that it will fill the requirement for "True RMS" readings.

On another note, I went and got some adapters to convert the 1/4" mono input jacks to allow them to accept my phone(RCA) jacks from my preamp. The newly received DH300 works but it has considerable hum through both channels (at zero volume) as soon as I plug the input leads from the preamp into the back of the Hafler. Both channels do work, so it's set up for stereo, although I have not done anything with the 2.2K ohm resistors I picked up, knowing my standard DH200 has that across the ground leg and chassis ground on the right channel. Could that have anything to do with the hum, or is it that I have some floating ground or something with these 1/4 mono plug inputs that I think are isolated from chassis ground.

R45 should be a 2.2 Ohm, 1/2W resistor. I would install that(if the 300 has none) on the right input, and see if that helps. But first: The AC plug on your amp should be ungrounded and non-polarized. Reverse(flip) it in the wall socket, before you do anything else. Then try connecting the preamp again. It's possible that the phase is reversed between the two units. If the RCAs that you bought at Rat Shack ground to the chassis: you'll have to find a way to float the right input, so it grounds through R45(if you're still humming).