Adcom 555 Mk 2 Questions

I'm a newbie here. I'm hoping someone is familiar with the Adcom amps & can provide some insight.

Long story short: My NAD 2600 blew up from static electricity. A friend who is not an audiophile has offered me an Adcom 555 Mk 2 really cheap for $150.

The rest of my system is: Teac Esoteric P-10 transport to PS Audio sl3 D/A by Illumanati cable. McCormick Line Drive Deluxe passive pre. NHT 2.5I speakers bi-wired. All analog wiring is Tara. Also have analog components & a Pioneer universal SACD player. Listening comments below are with the digital front end.

I just plugged the Adcom in (I'm told it hadn't been used much lately) & have 3 concerns. With all 3 concerns, my question is, "Is this normal behavior for an Adcom amp?

1. The heatsinks are quite hot from playing 4 songs at normal volume

2. There is some light hiss in both channels, even with the input muted. One channel has more hiss then the other

3. The amp is quite a bit brighter then the NAD. It may need to warm up for awhile (though again, the heat sinks are almost too hot to touch)

Thank you for your answers!
To add, just idling, this amp is REALLY HOT. I'm concerned about fire potential if I leave it on 24/7. Again, any educated comments would be really appreciated. Other then their power conditioner, I'm new to Adcom.
Something is wrong. I have 2 555s I use for bass amps and they do not run hot.
It is my understanding that Adcom had 3 different companies make the 555 at different times so there was considerable variation between samples. At least some of them were considered good at the time. I have never heard of them running hot. It sounds as if this sample has problems or possibily someone has set the bias very high. I would be leary of an amp running this hot that was not class a.
Sounds like your bias might need some adjustment and your amp could benefit from a good servicing. The upside is that they are fairly simple amps to have serviced and once running in top shape will have great sound for the $ 150 that you paid.
Adcom emailed me back. They say the heat is likely a bias adjustment issue & the differing levels of hiss could be of concern.

The person I got it from has 2 more, so I may try another, but I'm also not real thrilled with the sound. I didn't think anything could make my NHT's sound bright; I'm used to them being a bit on the dark side! Being on a budget, one of his other amps may still be a short term solution, though.

Thanks for all the replies both on & off list, much appreciated!
I've owned two ADCOM GFA-555s. On both the heat sinks got quite hot, "almost too hot to touch", with no ill effects. The longer they ran, the better they seemed to sound.
Abstainer, did you leave them on 24/7 (which I'd like to do)? I assume if so, you experienced no fire hazards...

The potentiasl for a fire hazard is my biggest concern. Sound quality is sadly somewhat secondary as I'm really broke right now & I suspect I'd eventually sell the Adcom if I buy it, but I'm so used to leaving all my gear on 24/7 I'm certain I'll occasionally forget to turn the Adcom off.

I still am looking into this between the pain of getting my NAD fixed & the cheap $150 price on the Adcom.

The one good thing about the Adcom is the static electricity that caused this in the first place appears to be gone.
Ironically after writing the above, I just noticed that I did leave it all night & all day today. No fire, but it's REALLY hot.
I am the original owner of an original model GFA-555. This amp has been on 24/7 its entire life - intially with Magnepan MG2, then small JmLab, and now Paradigm Signature 8 - the heat sinks on my amp never get hot - rarely if ever even warm - checked them just now - listening at low levels they are dead cold. This has been a great amp for me - maybe I just got a good one but I have always been very satisfied with the sound and performance of this amp. YMMV -

Moo, I've had a mkII for about 15 years without any problems whatsoever. When it was my only system I ran it 24/7. At idle it runs just slightly above room temp, but the longer/louder you push it the hotter it gets. Never really gets too hot to touch though. I recommend leaving it on 24/7 if possible for best sound. I use it sparingly lately and turn it off/on as needed - big difference in sound quality IMO. Not the smoothest amp around I'll admit but sounds very good with speakers that are voiced a bit on the warm side like my VA Bach Grands. Pushes them to the limit with great control. Probably not a great match for NHT which, from what I've ever heard, are a bit on the bright side.
Bottom line: still a great amp for the money though if the heat does bother you get it checked out.
FYI, it turned out the amp was bad. Hissing kept getting louder, then it died.

The person who I got it from had another. So far this one is running much cooler, with no audible hiss. I'm still not thrilled with the sound (though it may need to break in, I don't believe it's been used in several years). If it continues to be stable I think I'll buy it ($150) & continue to look for a repair option on my cheaper but better sounding NAD 2600. If I ever get the NAD repaired, I should be able to sell the Adcom at a small profit.
To clarify, it's definitely not ice cold like Kencrouch reported, but so far it's warm rather then hot.

I'm also running it on top of a cabinet rather then inside as i normally do (though inside is very well ventilated.).
Has anyone run these amps in mono mode? How did they sound?

I have a old 555 and I think it is a MkII because the RCA inputs are wide apart, not right next to each other as I see the originals are.
It has excellent sound. Not bright at all like some of the folks above speak of. I have it taking signals from a Dynaco Pass and feeding Acoustat 2s. This is great symmetry. The warmish Pas preamp and the big SS Adcom make beautiful music together.
I am interested in modding to some degree. First up will be cutting a hole in the chassis and installing a IEC plug socket. Afterwards the input board caps.
I don't see much to do to the power supply,since it is quite huge. This thing looks like a big empty box with one smallish board, a big toroidal and 4 big power caps.
Any mod info would be helpful.

I used an adaptation from an old Audio Amateur article to build a fully regulated power supply and it made a big difference in the sound quality especially with dynamic swings.

Hi, I know this thread has been going on for ages now. My opinion for the GFA-555 is a powerful and very quiet amplifier. Those who say it gets hot ,well there must be something wrong w/ it because mine does not even get warm under a heavy load. For the price used mine was $300 from Audio Classics sight and sound unseen just on reputation (SHIPPING THROWN IN ) and it came slippery clean and work the 2nd I hooked it up. I know tubes take time and I don't have the patience or that so I went ss and it's really instant on and does not get better the more you play.Yes when you shut it own and it spools down i does take a few minutes but who cares, your done listening. I sometimes leave the amp on all the time and I'm torn about this because most the people over on the POLK site swear by it and I must be a hypocric because  I have a sub woofer that has never been off since I got it about 9 y/o. For durability, price point ,looks, and form and function one could not  do much better.  For a starter amp or even your go to amp I would not hestate and go for it. My model is a bit different ,I have the rack face model used for recording studios because of their power and low noise floor. Highly recommended  for a step into 2 chll genre....Some say it's a bright sounding amp. I have no way o comparare and would like a Parasound or Bryston to get and hear the difference....Lew
Your adcom is too hot, hiss as well, it is sick and needs a doctor! My adcom gets a bit warm driving 8 ohm b&w dm4 spkrs at loud volumes and no hiss whatsoever.