Backiline 600

Got in under there. Anyone know what the temp setting of the S1 thermal switch is ? I'm reluctant to bend it back to reveal the other face as pins look semi rigid and probably not marked anyway. Not so straightforward a work around. Active monitoring with a TO220 device LM35DT, linear output, and perhaps JM65RC means selected for 65 deg C. Plenty of data on them but will have to sketch out the LM35 and 2 transistors to see a way around dropping 65 to 40 deg C in effect

Going to do a talk tonight on PbF and what do I find in this 2007 PbF amp? The self-tap screws supposedly holding the IEC socket to the chassis have no bite and so each insertion/pulling of the line cord plug, stresses the PbF solder joints on the pcb carying mains voltage . Solder OK at the moment but looking a bit suspect already and so a year or two on ,a conflagration in the making. So remedial solder and bolts and captive nuts replacing the self-taps.

The cut out sw is nearest the hottest part of the h/s so cuts out before the fan drive has really got going, it still has to cool down the bulk of the heatsink, all the while the underside is still going up. I can see a diode going in "under" the LM35 to raise the 0V output for 0 deg C to a voltage that will at least turn on the pass transistor to the fan, at room temperature, and then increase it with use. As it is the heatsink gets too hot to keep fingers on (50 deg C?) before the fan gets any voltage at all , surprisingly 24V but 3V will start to turn it.

I tested the cut out sw in situ. I can just see make out markings through the insulation wrap.

028 A 20 161 perhaps 161 deg F Sw goes o/c about 80 deg C and s/c again 65 deg C

Ask the owner, chances are they will want it on all the time. I used a Crown Microtech 1000 for a bass head for many years and it's still part of my rig along with a BBE 383 preamp. The fan was loud and ran full speed but the din of the audience nulled any noise it made between songs/ sets and of course when we played all you could hear during silent periods were your ears ringing.

The other great advantage with always-on is that the user knows the fan is in working order right from the off.

I remember my sarcastic drummer calling the Crown a microwave oven :) because of the fan noise. It never bothered me. Also used a BGW prior to the purchase of the crown. Larger in size but only 700 into 8ohms. It also had a loud fan but still hefty enough to have reserve on those low

5th string bass notes without distortion. That's the main reason I snagged the Crown. And I got many compliments from my band mates on the sound.

17 deg C / 0.17V of lift from a SM shottke diode under the sensor is about right to get the fan turning properly at ambient 15 deg C or more. Definitely a PbF solder amp from 2007. Made in China for USA for export to the UK but presumably the same for domestic USA use , no mention of PbF on pcb or rear of casing

If the amp is left switched on with no input the quiescent current is enough to slightly raise the h/s temp to about 30 deg C and fan comes on now I suspect the problem is drift over time of the Vbe of the drive transistor, change of 0.01V there leads to change of 1.5V on the fan , so if Vbe drops a few mV the fan will only come on at 50 or 60 deg C, too late to be safe

correction

so if Vbe rises a ......