Vintage HK protect mode?

How long a delay are you experiencing? More than 10 seconds? I recently had a very long delay -time issue with an NAD receiver that finally stopped kicking in altogether. After a little snooping I replaced a small capacitor that was located right next to the relay, thinking that it set the time constant for the relay to kick-in. On Power-up, the receiver stays in protect mode for about 4 seconds and then latches on as it was designed to. I would look for a similar situation in the HK. In the case of the NAD it was a 1uf at 50v electrolyitic capacitor. If you can find the service manual for the amp, it will show you the components around the relay for possible clues. Also, there is a thread at Audiokarma that tells how to check the dc offset values at the output of the amp. DC offsetthat is out of spec can cause an amp to go into protect mode, and is worth having a look at either way (if you're interested in a more hands-on appproach to maintaining your gear).

Yes. The warmer the ambient temp, the longer the delay--up to one half hr.

There were some Harman Kardon amps that went into protection mode if the preamp was giving some DC to its inputs. I can't remember model, or how many years back I heard about this. Maybe trying another preamp (no preamp if you feel safe) to see if this can be a problem. I can't remember if this happened right at start-up, or after the delay (few seconds?) turned the amp on, then went into protection.

OK. Thanks. I can't get back to you yet because I don't have the amp yet. It is being shipped. But this is very helpful.

It is just possible you are talking about a discrete 'time delay relay' which best case, is socket mounted.