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Old 21st January 2012, 05:14 PM   #521
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Quote:
Originally Posted by terranigma View Post
I ordered 50pcs Philips BCX56's for good price. I will solder their collector plate to a suitable copper heatsink.
The BCP56 is regular transistor size, possible to through-hole mount into good size via set into thick tracks. What also needs thick tracks is resistor drain since the resistor heat needs to be pulled away from the transistor--put the resistor heat into thick power rail instead.

However, the BCX56 version is very tiny SMD size. If using a normal soldering iron, you'll need a bamboo chopstick or kabob skewer to hold BCX56 down and prevent it from sticking to the soldering iron and/or escaping. Pre-tinning with Silver content solder and re-application of a thin film of Gel flux makes the process very fast. These need thick/reinforced tracks because they use both tab and pins for heatsink.
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Old 21st January 2012, 06:24 PM   #522
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If you will not use them on smd pcb, their size difference doesn't make a lot of sense. BCP's leg distance is 2.3mm, BCX's 1.5mm, which is fair enough. What I like with BCX is its whole collector plate is naked Thus, if you attach/solder it to a wider plate, heat transfer from chip die should be done directly and more efficiently using its wider area. I didn't choose BCP's because you can only see a part of its collector plate.

Last edited by terranigma; 21st January 2012 at 06:27 PM.
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Old 21st January 2012, 11:46 PM   #523
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I'm still soldering this little copperless perfboard version and its job is to make a nice new layout; however, it isn't conducive to test driving different parts and options.

Does anyone have a nicely spread out board for sale? One of the "RF proof" editions would be fantastic, despite the few jumpers.
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Old 22nd January 2012, 12:38 AM   #524
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I wonder MOSFET for Q5 & Q6? Would maintain input pair at more constant current?
Even with quadrature trying to disturb this, the collector resistor drops would drive
fixed gate threshold voltages, and no base current leak. Currents can't drift far from
this mark. R6 R7 obviously must scale up as VBE becomes a slightly larger VGS.

Wacky drain capacitance is my only concern. I don't know how to guarantee any
simulation behave realistic in that regard. IRF510 (100V,0R5) IRF610 (200V,1R5)?
either claims about 16pF, if only that cap would stay put and not squirm... You
got 820pF sandbagging from anode to anode, it seems reasonable in that light.

Is R5 in the second tail actually helpful? Considering its position within both
closed loops, the closed loop balance and non-shutoff here is already forced...

I was never all that clear about how one calculates loop stability to begin with?
And as we throw another loop at 90degrees effect into the blender, I get really
confused what effect the compensation is having upon each... If push and pull
are each doing nothing at some current minimum for slightly less than half a
cycle, differential compensation is clearly also active in the common mode loop.
I'm not saying that's a bad thing, it might be a good thing? Only it's an I don't
have a clue how to grasp for the math of it...

Last edited by kenpeter; 22nd January 2012 at 01:08 AM.
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Old 22nd January 2012, 05:26 AM   #525
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Not quite sim ready yet, just another half-baked noodling...

Not sure I got the fuzzy thresholds of the logic function quite right?
Pull the LTP up to try and shut it into class B. Then if either output
would actually threaten to go B and shut off, I pull down on the LTP
until the threshold of true shutoff is never quite met?

Moto 4N25A spec sheet suggests 1V15 to 1V5 might be threshold for
the LED? Seems a little too temperature dependent for the purpose...
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Old 22nd January 2012, 10:12 AM   #526
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Question: Is it okay to test Circlophone without the output devices connected?
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Old 22nd January 2012, 03:19 PM   #527
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If you also do not connect a load, perhaps the drivers (Q9 Q11 schematic #1) alone
could satisfy the output stage crossing current rule? Be warned, if they conduct more
than 200mA continuously in attempt to do something stOOpid, like drive a load, or
fulfill a maladjusted rule requiring higher quiescent than 200mA, they will probably
burn up. If those drivers are not heatsinked, I would not even attempt it....

The outputs are also current dumpers for the drivers. Normally, drivers would never
be asked to conduct such current by themselves...

Last edited by kenpeter; 22nd January 2012 at 03:24 PM.
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Old 22nd January 2012, 06:53 PM   #528
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Right now I'm attempting a baseline example to see what a normal Circlophone could do. ♫♪ The Inexpensive Circlophone© ♫♪ It is very much like post 1 with some of the expense subtracted and a slightly different voltage, aimed at 4R to Tip35c, and seemingly keeping the parameters normal.

Unfortunately, I had managed to connect a possibly decent predrive to a erroneously haywired output section, somehow confusing a topside photo with a trackside photo, and that smells awfully. Visible damage looks inexpensive, with 1 Tip35c and 2 resistors nonfunctional.

However, the drivers need checked out somehow. The load that I was planning to drive with them is an ac voltmeter, hoping they can produce signal. For repair, I do have more ST Tip35c, but unfortunately, no more 2SB649 at the moment and I do not know if they survived my wiring error. I do have "Authentic Chinese" Fairchild BD140, which might not be that good, but of course might have to find out. . .

P.S.
HFE matching efforts reveal that NOS Philips BC556B is much like other manufacturer's BC560.

Last edited by danielwritesbac; 22nd January 2012 at 07:08 PM.
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Old 22nd January 2012, 07:44 PM   #529
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Daniel,

You should connect an old type 60W bulb in serial with your mains legs (like fuses on mains), just prior to the transformer. This is one of the thumb rules while first powering up an amplifier. When you see the bulb lights up shiny, you have to suspect something faulty on circuit. If you see bulb's filament in dully reddish color, you can begin to measure dc-offset and current draw by amplifier.
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Old 22nd January 2012, 07:52 PM   #530
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Muntz'd an entire current mirror, yet kept drain voltages ~ equal.
What more to be simplified and still obey laws of circlophonic logic?

I am still uncertain 4N25 optoisolator will conduct the required current.
The curves stop at 1mA, even though spec suggests it could go higher.
Maybe time to dig up the 9610 .model and see what LT thinks of it?
If the optos don't reduce complexity, really no point to them...
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