What you describe does not sound normal. The amp should not be running that hot. Have a technician check the bias, which may have drifted over the years. The amp is more than 30 years old and should be looked at anyway.
I believe Gbart is correct, I use to have Sansui amps, 919, AU-X1 that I remember and they did not get hot. The only other time an amp will get this hot is driving a load that it is not really up to and the Sansui amps were quite powerful for their day. If you have driven the same speakers to similar volumes with other amps with no problems then you should have it looked at. A good idea in any case with an amp this age.
What speakers are you running with your AU-719? Sansui and other similar amplifiers from the late 1970's are rated for 8 ohms. Nowhere could I find a 4 ohm rating for these products. The speakers your AU-719 was designed to be used with have sensitivity ratings ranging from 92db to 105db. Depending on the sensitivity rating of the speakers you are currently running and the gain in your source half volume could easily be full volume.
I'm using the same set as I was with my other Sansui Amps, 8 Ohm speakers. I have not changed a thing, other than the amplifier.
I had a couple of those amps through out the years from horse trading and they do run a little on the hot side. They are biased more on the A side but they should not burn you. It is a high current design and should run most speakers from 3 to 16 ohms with no problem. Your amp needs to go to a technician for tune up and anything it may need. vinyl on dude.
"I'm using the same set as I was with my other Sansui Amps, 8 Ohm speakers. I have not changed a thing, other than the amplifier."
Do they have a name on them? Check the back of the speaker. Sometimes there is a label with the brand and the model number.
I use two sets of speakers on this set up, the mains are Sansui SP7500X and the satellite speakers are Paradigm 5SE. That is the current set up.
Anyway, thank you kindly for the help, it is much appreciated, at least now I know that there is a problem and I will have someone check it out, once again, thank you very much;
Your problem may be running 2 sets of speakers IF you are running them at the same time. Try disconnecting the satelites and see if the amp still runs hot.
I could give that a try but all my other amps did not run this hot with the same speakers hooked up.
Well, that is new, V. important info (running two sets of speakers). Resistance in parallel is calculated by the formula Rt = R1xR2/R1+R2, where Rt is total resistance, and R1 and R2 are the resistances of each individual set of speakers. What this means is that the resistance (or more accurately, impedance) that the amp "sees" is less than that of the lower of the two sets of speakers. Can't find specs for the Sansuis but the Paradigms are 8 ohm nominal, which means that the max load the amp would be seeing is 4 ohms IF the Sansuis are 8 ohm speakers. The amp's specs are only given for 8 ohms, so its reasonable to believe that this vintage unit's power supply is not up to the task of driving a 4 ohm (or lower) load. given that the nominal impedance is likely lower at some frequencies, this could easily end up with a combined impedance of 2 ohms or less. Your amp is very likely getting very hot because you asking it to produce more current than it can safely do. NEXT STEP; BLOWN FUSES IF YOU ARE LUCKY, OR BLUE SMOKE AND TOASTED AMPLIFIER IF YOU ARE NOT.
I checked with a 1979 isssue of HI -Fi Choice. The 719 was not tested but the 417 would produce 80 watts at 8 ohms tested driving one channel only it was 100/150/171 at 8/4/2 ohms. Burst power was 130/211/300. For the 919 the numbers were 145/210/275 and burst power 164/314/543. The 719 should be between these closer to the 919 than the 417. Burst power is a measure of short term capability that is relevant to performance on music which generaly does not call for constant full power. These numbers make me think that yours is not working properly.
Specs for Sansui SP-7500X are as follows:
16" woofer; 6 ohms
8" midrange; 8 ohms
6"x2" horn; 8 ohms
2" tweeter; 8 ohms
Stanwal, Please explain. I don't understand how the numbers you posted make you think the OPs amp is not working properly.
I think the easiest test would be disconnecting the second set of speakers and only running the Sansui SP-7500X, the speakers the AU-719 was designed for. This would be much easier than having the amp checked by a tech. The OP also mentioned in his post playing music at half volume which I assume is the 12 o'clock setting on the volume control. This setting could easily be approaching the amplifier's limit.
Although the model numbers are similar the amplifiers can be quite different on the inside and I believe the AU-719 was designed different than previous models.
I would suspect filter caps that have dried up some and are becoming resistive producing heat as well as output transistors that maybe seeing a higher bias than they should be and heating as well.
Thanks again, I'm going to try to get someone to look at it as I discovered another problem last night. The Tone Defeat switch works just fine in the "Defeat" position" but in the "On" position the right side cut out on me (although it had been working just fine in the "On" position up til then). I cleaned it prior to hooking the amp up last week. I tried it again this morning and once again the right side cut out so I moved the switch up and down quite a few times and sometimes all four speakers would work, sometimes just one side would work and a couple of times neither side would work (while in the "On" position / all four speakers seem to always work in the "Defeat" position though). I don't think that has anything to do with the excessive heat but as I'm finding out, this unit has some issues. Later today I'm going to try it with just two speakers and see if that makes a difference with the overheating issue, then I guess I'll just have to hook up one of the other ones for a while and see about getting this one fixed, Thanks again for all the help, I really appreciate it because if you haven't already noticed, I'm not exactly technically inclined when it comes to these things:)
Just listened to it for about 40 minutes with only the two main speakers hooked up and it still gets extremely hot. I had the volume at less than half (or at about 11 O'clock). Time to hook up a different one and once again, thank you for the help.
I don't know if this is worth mentioning but I unhooked the 719 and hooked up my little 417 and it is driving all four speakers without breaking a sweat, it is barely warm.
What they indicate is that the amp should have no trouble driving 4 or even 2 ohm loads. Amps that have trouble with lower impedence loads see their power stay the same or decrease as the impedence falls. The Sansui's rise in power indicate that they should handle lower impedence loads. The OP's last post seems to be vindication enough for my position. The smaller 417 has no trouble, the 719 does; ergo the 719 is not opperating properly.