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SANSUI AU-719 Gets Really Hot?

I recently acquired a Sansui AU-719 which gets extremely hot. I have other Sansui's (AU-417, AU-517, AU-717, AU-7700, Etc.) and though they do get warm, none of them get anywhere near as hot as the AU-719. I listened to it for about 6 or 7 hours the other day (I only listen to vinyl) and as happens from time to time, after a few beer, the volume tends to go up:) Still never exceeded half volume and it was more than loud enough (think the neighbours hate me now), yet it got extremely hot, so hot in fact, that I could not keep a finger on it for more than a second or two for fear of actually getting burned. If this is normal for this model then I can hook up a small fan near it to help dissipate the heat. Today I've had it on for about 2 hours at just less than 1/4 volume and it is a bit warm but by far not too hot. I tried researching this on line and found two opposing points of view, some said it is normal while others said that the excessive heat probably indicates a problem which if it not fixed, could fry the amp. Any input would be much appreciated, thanks;
Denny
recordman34
recordman34 OP
7 posts
 
I could give that a try but all my other amps did not run this hot with the same speakers hooked up.
swampwalker's avatar
swampwalker
5,138 posts
 
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.
stanwal's avatar
stanwal
3,147 posts
 
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.
rrog
1,958 posts
 
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
rrog
1,958 posts
 
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.
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