Official M2 schematic

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#2,582
I have variac .......
 

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#2,583
mpmarino said:
I'm building a + / - 24v 'universal First Watt' PSU in a separate chassis.

Except for the reason of heat dissipation, My amps can be rather small, at least smaller than usual.

I had in mind to use four of these smaller sinks for an M2. I was a bit worried if they would do the job... borderline maybe. I did some calculations, but didn't trust it much.

I decided to clamp an IRFP140 to it. I biased it up using a 24V supply, .4R source resistor, and a pot to adjust the bias. Running at 1.8A (0.6A excess over M2 bias for safety margin) I could only get the sink to 50c after several hours. I could top 60c with over 2A bias. This is in a 'room temperature' room.

I can be reasonably sure that these sinks are good for the application. I'm thinking that this is the best way to truly evaluate heatsinks with unknown (or even known) specs.
Click to expand...

Unfortunately I don't have a brain so the calculator and variac are just looking at me waiting to do something ... :ashamed:

So 24V @ 1.8A = 43.2W you're pumping into one heatsink, so assuming the 2 devices are paralleled or complementary you'll be good for at least 86W dissipation right (because you're going to use 2 per side)?

For power resistor and variac, would you have to measure the voltage drop across the resistor to figure out the current going through and then measure the voltage to do the calculation? You'd need some pretty big power resistors for that correct? Would dummy loads work for that?
 
#2,584
twitchie said:
...

So 24V @ 1.8A = 43.2W you're pumping into one heatsink, so assuming the 2 devices are paralleled or complementary you'll be good for at least 86W dissipation right (because you're going to use 2 per side)?

...
Click to expand...

Yup, two per side.

you'd have to subtract the heat from the source resistor...

1.8 X 1.8 X 0.4 = a whopping 1.3 watt break 🙂

But my theory is really to mimic the situation - in situation. If the M2 biases at ~1.2A as I did on the bench with a couple of parts (only the top of the OP section as an example = 24v) then I expect my sinks to hang around 40c.

The whole thing could be flawed, I haven't a brain.
 
#2,590
Just another datapoint. I built my M2 with 10mA jfets because that's what I had on hand. TeaBag board and corresponding standard BOM + resistor change to help bring the DC offset to zero. Sounds mighty fine to my ears and still my favorite amp. Hundreds of hours on it and zero issues.


BK
 
#2,599
When I measure the DC resistance of the Edcor primary, I get about 44 ohms. (average of two transformers)

If the DC offset voltage at the output of the 2xJFET input buffer circuit is 0.1 volts, that results in a DC current of 2.3 milliamps flowing in the primary. {Ohm's Law: I=V/R} I don't know about you but I don't want 2.3mA DC, flowing in the primary.
 
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