I'd recommend you have it checked to make sure the power supply capacitors are still good. The large electrolytic caps in power amps often go bad after 20 or 30 years. The results can be devastating to speakers. This amp is at that age.
The issue is money. IF you spend the couple of hundred dollars to have it 'checked, and the caps replaced' then you still have an amp only worth a couple of hundred bucks.
My being a real cheapskate, I would just use it. And not worry about it. If it currently is working, why fix what is not broken?
And yeah if you had buckets of money get it checked. If not, then take MY advice.
But I think if you had buckets of money, you would have had a better amp than this hand me down.
So do not worry about it.
Musical Concepts can help you a lot with this old Hafler. If your brother "gave" it to you, then you might want to spend a little to "freshen" it up.
I spent $1200 to upgrade my DH-500, and the sound is more neutral then my Mac. I also plan on keeping the amp till I die. By the way, I read on this forum where one guy described the looks of the DH-500 as "early World War 2 submarine radio style"
Elizabeth makes some very valid points. Just for a tech to look over an amp by me is now $60 to $75 depending on the equipment. Then after all their work they could be into you for hundreds and if you were to sell the DH500 you would lose out. Musical Concepts is a whole other story. I once had a Hafler XL280 that was modded by them and the music was really nice.
Now when I had the Hafler DH-500 one thing I did was clean the insides of it. The fan inside the DH-500 will bring all sorts of dust into it. I bought some cleaners from Radioshack and sprayed the boards. The speaker terminals and IC posts were sprayed with DeOxit. I vacuumed what I could with a small vacuum cleaner.
On a popular auction site if you search for Hafler of Hafler DH you will find repair kits that aren't too much money. There were replacement Power Supply caps for $50 that looked pretty easy to install.
Also the looks of the DH-500 are on point with what Paul_graham said. The green color scheme and looks of the DH-500s are really military like. Drab and all business. Nothing pretty at all except for the sound. All in all I wish I still had a DH-500.
The one wild card with Elizabeth's advise is the potential for damaging your speakers. If a cap goes bad in the wrong way, its just not the amp at risk.
I'd upgrade it or dump it. Its too old to plug in.
If your speakers are fused, that may help protect them. Also, you could add your own inline fuse. Possibly a 1 and a half amp, to two amp in series with the plus terminal of your speakers. A low powered new amp could clip out and fry your speakers on the spot too. There was a recent thread with a guy with expensive speakers, and amps that blew the midranges just from playing them a little to loud for awhile. It depends on how much you want to spend, but I would still put fuses inline with them, new or old amp. If there is any sound loss that anyone could hear, it far outweighs having no protection after something may go wrong. Well respected hi-end speaker companies use fuses to save them.
Thanks...someone mentioned the color green but mine is a flat black. Also this amp does have inline fuses on each side. The fuse caps say 10 amp, but i guess you could use a lower rated one for added protection.
Larryrx, the amp manual states it comes supplied with 2 amp fuse for speakers. I don't know if those are the correct covers, or fuses for something else. They like the 2 amp apparently also. Read last paragraph, page 4 in link. That way you could decide. A 10 amp will let most speakers get damaged. Page 4 Under "Loud speaker fuse protection" [http://www.hafler.com/techsupport/pdf/DH-500_amp_man.pdf]
Oops, page 4 "loudspeaker fuse selection"
It's hard to say not knowing the rest of the system.
That said, stock, the DH500 is not very good. In it's day, and I had one, the little Amber 70 kicked it in the butt. The biggest problem was the Hafler sounded anemic. No dynamics. Sounded like a 50 watt amplifier rather than 500.
I had also gone the Musical Concept routs, though with an earlier DH200, rather than 500. John's kits do improve the sound but it's still going to sound like a solid-state amplifier from that period and not up to the standards of equipment being built today. So if this fits into your budget, then you consider the update. Otherwise, I'd save my money and look elsewhere--but as I said in the beginning--it all depends on the speakers being used, etc.
And here you have the Audiophile dilemma.
Suggestions from tossing it, as it is a chunk of crap anyway, to upgrading it for a thousand bucks..
Good luck, whatever course you choose.
(The speaker line fuse reads like a good idea. the least expensive safe route IMO.)
I am using this amp with a set of Meadowlark Swift. These are very easy to drive and the Hafler does a reasonable job. I use a Red Wine Audio modded Squeezebox 2 as a source and a Sunfire Reference preamp as a control unit. For almost zero investment, it ain't bad. I have heard worse for a lot more money. I am basically a tube man so the limitations especially in the midrange are apparent. My experience with alot of these large power amps is that they sound better when played louder than I normally listen. Tube in contrast seem to retain there dynamics at a lower volume level..Does anyone else feel the same?
Well Elizabeth, I consider my purchase of the DH500 as one of my two worst decisions in my 35 years of audio (the other being the Adcom GFA-1 that couldn't drive anything but a 8 ohm speaker and would overheat and constantly shut down driving my DQ10s :( ). The 500 was a step down sonically from the 200. Perhaps they cut corners when it came to the power supply and upgrading that might improve the sound of the DH500. I kinda doubt it though.
"Tube in contrast seem to retain there dynamics at a lower volume level..Does anyone else feel the same?"
I do, and the lower I go, the more "single ended" seems to be the best. There are exceptions of course. I was surprised at how good my ss Pass XA.5's sound a low volumes. I read Nelsons description of the circuit and guess what? He biases these to run "single ended" at very low volumes. Even at louder volumes, you have times where the music decays into silence.
I think it is a tough call;would you consider using it for subwoofer work or surrround processing if you have that as a option?
Since you mentioned that is has not been used for many years I would have it looked over especially the power supply filter caps if they are still the original.