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Need help for transistor ID, substitutes, and pinout (rare MC plug in board)

dogwan

dogwan

Dogwan
Hey all, I have this apparently very rare MC board out of a mid-70's PSE Studio One preamp. Decided to start a separate thread since it's really just about the transistors, not the preamp itself.

I discovered the MC phono input was not working so I pulled the board out start testing the transistors and caps. Quickly found the complementary pair of transistors at the power input to the board were both toast. Normally if I can't locate a datasheet for a transistor I will look for another of the same to pull and test to at least get the pinout and determine if it's a NPN or PNP. This board is the only place these transistors were used in the entire unit.

So, my issues are:
  • I am not 100% sure of the transistor part #'s.

    One says BC 340LA and I am pretty sure it is a BC340?
    The other says 320L and suspect that it's BC320, but the only BC320 info I could find shows TO-39 (not TO-92 as shown).

  • Unable to find dependable datasheets on either of these transistors (even if I was positive on the ID), so cannot be sure of the pinout.

  • Unable to determine suitable replacements (even if I was sure of the ID).
Here are pics of the transistors.

I am also attaching sketches of the circuit. There are most assuredly mistakes, but I am confident of at least the general idea. And I paid particular attention to the two transistors in question (circled in red). I labelled the pinout on the connections.

So if anyone can verify ID, suggest replacements, and most importantly, tell me what the pinout (CBE, EBC, BEC, etc) should be based on the diagram?

Note: as you can see the pinout appears to be different between the complimentary pair. Also, the measured voltage between the positive and negative leads is 60vdc. When measured to ground it is +30 and -30, so I assume it is balanced. All other transistors were pulled and tested good. Caps all test decent.

thanks,
Dogwan

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petehall347 said:
try this data sheet .
https://html.alldatasheet.com/html-pdf/75194/MICRO-ELECTRONICS/BC320/1444/1/BC320.html

pic of one here shows EBC .....https://www.radiomuseum.org/tubes/tube_bc320.html

some show as looking from the legs side .
Click to expand...

I suspect that the pinout differs between manufacturers. That radiomuseum page shows it labelled EBC in the pic, but in the diagram right below the pic it shows CBE!

I think at this point I just need to confirm on the diagram I drew what leg should go where and go from there. Unfortunately I don't know enough about the application to make that call myself.
 
The schematic shown does not indicate what the transistors do. However, it WOULD make sense if these devices were voltage regulators.
A BC340 is definately a TO-5 type of transistor...
So this did lead me to google your problem making these assumptions.

Here may be your "320" which popped up https://www.jameco.com/z/79L12A-Maj...V-100mA-Negative-Voltage-Regulator_51431.html
It also has 320 on it.

Probably the "BC340" will be a positive 12 Volts voltage regulator....

https://www.digchip.com/datasheets/parts/datasheet/321/LM340L-pdf.php

In the end, you already found out yourself they are providing power rails.
 
Last edited:
gslikker said:
The schematic shown does not indicate what the transistors do. However, it WOULD make sense if these devices were voltage regulators.
A BC340 is definately a TO-5 type of transistor...
So this did lead me to google your problem making these assuptions.

Here may be your "320" which popped up https://www.jameco.com/z/79L12A-Maj...V-100mA-Negative-Voltage-Regulator_51431.html
It also has 320 on it.

Probably the "BC340" will be a positive 12 Volts voltage regulator....

Or was somebody in there before and mistook the regulator for a transistor also, and National Semiconductor did make a special "BC340" in TO92 package (adding a suffix).

In the end, you already found out yourself they are providing power rails.
Click to expand...

OMG, I think you're right. I was looking at this all wrong. I let the form factor of those transistors steer me towards NPN/PNP pairs. The BC on the "340" threw me. I searched LM340a12 and got a matching +12v regulator!

The pinouts on the LM7912a and LM340LA12 match the pinouts on my diagram and are as follows:

LM7912a
1 = ground
2 = -Vin
3 = -Vout

LM340LA12
1 = +Vout
2 = ground
3 = +Vin

Thank you so much!
 
gslikker said:
I googled your amp, it looks a pretty scarce device :)
Click to expand...

Yes, the preamp is rare. The optional MC board is even rarer.

The whole PSE line is very well respected, but it wasn't widely distributed. It all has a cottage hand-built quality to it.

I'm sure this mid-70's MC head amp could easily be bested by modern circuits or even an SUT. But, due to the rarity I have a vested interest in getting it working again.

I already have replacement regulators loaded into into my shopping basket on Mouser.
 
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