I know how hot my amp is, do you?

wattsabundant

wattsabundant

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#1
Several years ago I bought a computer fan controller with thermocouples to mount on heatsinks and a variable output to drive 12 VDC fan motors. As heatsink temperature rises, the fan picks up speed. The controller fits in a 5.25" floppy drive bay. I bought a stand alone case and mounted the controller in the case. It worked but I didn't have the time or means to put it all together. Mounting the thermocouples to a heatsink was a problem.

Today you can buy 2 rolls of double sided heatsink tape on Amazon for $10. The contoller can monitor up to 5 devices and independently control 5 fans. I mounted the thermocouples close to the outputs on 700B in the pics. Mounting to the transistor case is asking for disaster as they run at +/- 100VDC and Im sure the thermocouples aren't rated for that. 4" fans will fit snugly between the heatsinks on 400"s. On the larger 700 they are standing alone with no support.

I've did a considerable amount of destructive testing on 400's when I developed the relays boards. With only one output in a 400 it will blow the transistor in a minute or so when running bout 70 watts which is worst case condition. I consistently recorded case temperatures above 140 degrees C at time of failure.

Now all I need is a night to rock out and see how it works. The Marantz in the pictures is for show only. I couldn't see keping it on a shelf in the basement..
 

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orange

orange

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78F over several hours for the Sansui RZ-9500AV.
 
Fishoz

Fishoz

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You should see the hot little red and black string thingy I got it for V-Day....gonna need a leaf blower to keep 'er cool.....

Serious though....she cut out on me the other nite...playing at just under the level before the room took over. Not the first time it has happened but it is rare. Preventable with a fan...I'm sure but for the few times it happens, necessary????
 
grapplesaw

grapplesaw

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wattsabundant said:
OH yea. I did everything but the LED board last year. The LED board was a couple weeks ago. I may try changing out LED's
Click to expand...
I am with you Don
I have a warm white led board I am going to put in my next build. I find the blue is nice color but had to see the meters.
 
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wattsabundant

wattsabundant

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Referring back to the fan controller testing, I have JBL4412's and a JBL B380 sub in the 70's room. Where possible all of the gear is from the 70's. I use a P/L 400II on the 4412's and one channel of the 700B on the sub. The crossover is a BGW model 20. I got to know the BGW when I worked at a pro sound shop in the early 80's. It has a summed sub output that I set for 80Hz.

The 700B is in a cabinet and sits on top of the sub. As you can see from the picture I posted, the controller was sitting on an ornamental Marantz Model 26 receiver, which was sitting on top of 700B.

Thursday night the wife went to yoga and I went to work with Rage Against The Machine. RATM because the drums and bass demand lots of volume. The room is 13' x 15' with carpet, drapes a couch and a couple cloth chairs. No sooner did I start the test and the controller started rattling from the sub. Due to the short leads on the controller I couldn't move it conveniently. I quieted it down by sittiing a couple pot holders underneath it.

It was painfully loud trying to get the 700B heated up. The heatsink temperature, according to the contoller, never got above 27C which is about 80F. This was with one 12V fan at 60% speed blowing on the heatsink. Fortunately the fan stalls easy because I got my fngers in the rotating blade a few times. No damage. I then set the fan, face down, and after about 10 minutes the heatsink temperature was only 40C (105F).

The 400 sits in a P/L wood cabinet and it in turn sits in a converted TV cabinet with a back on it. Above the 400 is another P/L wood cabinet with a 3300 preamp and 5000 tuner. The preamp and tuner fit nice in the 4 space cabinet. The front panel of the 400 was warmer than the 700B during the limited test. There is no air flow around it. It is a major pain to take the 400 out of the TV cabinet and getting heatsink temperatures was not possible.

Tonight I was doing some bench testing with the stock Clair 700II I got from Perry. The only thing I've done to it was install a relay board, change the 9800uf caps (one had vented and spewed) with 15,000uf, replace the electolytic caps on the driver and added a 10uf cap on the zener power supplies. I also replaced that stupid 7.5K/2W resistor on the driver board that likess to fail.

I have a CD player in the rack by my bench and used the headphone jack out of the player to drive the Clair. The line out of the CD player goes to a Sony STR GX10ES receiver located in the top of the rack for music playback. With this arrrangement I was able to drive the Clair amp with music as hard as I wanted, under resistive load, but not shatter windows. I drove the Clair into Dale 8 ohm/250 watt resistors.

The intent for this test was to get an idea of how hot a 700 would get when driven into hard clipping with music and no fans. The headphone output level wasn't high enough so I used a P/L X20 pro crossover to boost the signal. With Rage dialed up again I watched both channels on the scope and had low volume out of the Sony.

The only time the amp clipped hard was from the kick drum. This time I used a laser temperature gun to shoot the outputs. After about 10 minutes the drivers were all under 30C. The bottom output on each channel was in the mid 30's. The second output up from the bottom was a few degrees warmer than the first one. The top 3 ouputs on all heatsinks were in the high 60's. The heatsink closest to the transformer was the coolest followed by the one by the I/O jacks. The two middle heatsinks were typically about 5 degrees celsius warmer than the outside heatsinks. I shot all of the trasistors several times as fast as I could. At one point the temperatures seemed to drop a few degrees which I guessed was the bias transistor backing off the bias. That's when I stoped the test.

70 degrees C (160F) may be hot to the touch but is not all that hot for power devices. Last year I did some testing on a 400 with only one output on one heatsink. The single output routinely failed about 150C as measured with the same gun. That is hot.

Conclusions: I was really surprised at how well the heat was distributed given this amp is decades old, is in stock form, and saw road duty. I may try doing the test again with one channel to see at what point it fails. On second thought I'll probably do that on a beat up 400.
 
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