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Old 22nd September 2011, 12:41 AM   #31
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Location: Dallas
Quote:
Originally Posted by kenpeter View Post
Doublecheck against schematic before cutting anything.
Guesswork of a madman with no guarantee of any sort..
I don't own one, never tried it. You take your chances...

Does not include fix for current mirror with the miswired
transistor. Somebody else can draw that one.
Actually, you may not have to cut anything to fix the
current mirror. 2n5551 default pinout of EBC is problem.
Fairchild spec sheet mentions 2n5551-C (note suffix -C!)
pinout of ECB would probably fix everything, no knife...

Were any other 2n5551 lay'd out for ECB? I'm still chasing
traces around to see what goes where...

-----

Other three 5551 strapped as diodes could not care less.
EBC vs ECB, same circuit either way.... Use whatever...

Its only Q2 where Fairchild -C suffix pinout might matter.
Q2 seems to be 2n5551 nearest the MX50 logo.

Last edited by kenpeter; 22nd September 2011 at 01:03 AM.
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Old 22nd September 2011, 12:50 AM   #32
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I have seen similar oscillation on a quasi design of mine I was testing.
C12 and C7 need increasings to get rid of the oscillation.
47pf or maybe 100pf are worth trying.
The amp is simply unstable.
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Old 22nd September 2011, 01:11 AM   #33
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If not confusing enough, Philips spec sheet shows CBE pinout!
I think its same as Fairchild EBC default, just disagree which end
is pin 1... If you go by the D shaped outline, its all same same...

But you need ECB, not the default pinout of either mfg.
Else you will be twisting legs or cutting traces for Q2...

Last edited by kenpeter; 22nd September 2011 at 01:17 AM.
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Old 22nd September 2011, 06:04 PM   #34
sbrads is offline sbrads  United Kingdom
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I've just tested one of the kit's 5551 NPN transistors, it checks out as BCE pinout, gain 150. That would make the Q2 pin nearest the MX50 logo the emitter. I think that makes the pcb OK, it's the schematic that's wrong at Q2. Brain hurts - I'll take another look at the weekend.

The 5401 PNP measures gain 200 and has pinout CBE.

Last edited by sbrads; 22nd September 2011 at 06:06 PM.
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Old 22nd September 2011, 07:23 PM   #35
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I posted that original schematic which is what I got from the seller. There were problems with the drawing in the bias adjustment circuit where I was having trouble. I traced out the PCB and corrected that schematic before posting it. Didn't do that for the current mirror, but wouldn't be surprised if there was a problem with the Q2 & Q4 part of the schematic.
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Old 22nd September 2011, 07:57 PM   #36
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OK, just looked at my boards and the transistor datasheets. My kit was shipped with NCC 5551 transistors. The datasheet is here:

NCC 5551* datasheets and application notes, data sheet, circuit, pdf, cross reference, pinout, datasheet | Datasheets.org.uk

Looking at the traces, pin 1 (emitter) on both Q2 & Q4 are tied together and go to the minus supply post the RC filter. Then pins 3 (collectors) are tied together, so it seems the schematic is wrong and the PCB is correct.

All of the traces of interest are on the back side of the PCB. In your picture, you placed a dot under Q2 on the back side of the PCB. Q4 is to the right. The pins on both transistors top to bottom are:

E
B
C

Your picture is repeated below for convenience...

Click the image to open in full size.
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Old 22nd September 2011, 11:44 PM   #37
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Collectors (dot end) tied together matches schematic, but makes no sense.
In a current mirror, bases are usually tied together, and one collector only.
I stand by my statement that ECB pinout is required, at least for Q2...
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Old 23rd September 2011, 12:38 AM   #38
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You're right, Q2 & Q4 are not wired as a current mirror for the long-tail pair Q1 & Q5.
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Old 23rd September 2011, 01:36 AM   #39
ljm_ljm is offline ljm_ljm  China
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Oh I'm sorry my English is not very good, what question?

This is my products.
And I want to explain the CC5551 feet, a is the ECB.

this is sch,
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Old 23rd September 2011, 01:54 AM   #40
ljm_ljm is offline ljm_ljm  China
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In addition I explain, this version called MX50X2.

Not MX50, because my another version of the son also called MX50. smile

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