P3A amp - BC546 Placement

dine1967 · 2nd January 2003, 01:23 PM

Folks, Happy New Year

Iam in the process of assembling a P3a amp. The layout on the PCB suggest that the transistor pins are arranged (looking in the front of device from left to right) as collector , base and emitter. I checked this a number of times to make sure.... hope iam correct. However, the datasheet for BC546 (philips) suggest that the transistor pins as emitter , base and collector for the TO-92 package. Iam a bit confused on the transistor placement.Is the transistor to be placed by turning it around? thanks in advance

sam9 · 2nd January 2003, 02:48 PM

It is quite possible. The NTE cross reference guide cautions on this. Appearentlt the leads are not consistent between manufacturers for some TO-92 types. Having stumbled on to this in the context of PCB layout software, I always double check the lead configuration of the device vs. the PCB pattern.

tiroth · 2nd January 2003, 03:15 PM

Yes, be very careful. I ran into this problem also.

carlmart · 2nd January 2003, 03:26 PM

Looking at an old Cricklewood catalog that I have, that usually served me to identify transistors, if you lie down the transistor, with flat face up and pins toward you, what you have is:

collector-base-emitter

From left to right.

Don't you have a multimeter to test that? In any case it should be better for you to match input tansistors for same Beta.

Carlos

MikeW · 2nd January 2003, 09:09 PM

Use the data sheet for the transistors you have and match up the correct pins. They may or may not match the board. Good luck.

Rory Christ · 2nd January 2003, 09:31 PM

Both the PCB and the data sheet are correct. The data sheet shows the pins from the BOTTOM of the device rather than the top. Once you look at it from this perspective, it all makes sense. Confusing? You bet!

I am referencing the following: http://www-us.semiconductors.philips...C546_547_3.pdf

I only realized this after I installed all my transistors backwards because I incorrectly assumed the diagram in the data sheet was a top view.

OliverD · 2nd January 2003, 09:33 PM

One thing worth mentioning is that a circuit can possibly work even if C and E of some or all transistors are swapped.

I had this problem several times - why do two amplifiers built on the same PCB, wired with the same cable, housed in the same chassis sound and perform so different? Took me days to figure out :-)

I don't know a way of finding out whether pinout is E B C or C B E with a multimeter... B C E would be easy, but...

Cobra2 · 2nd January 2003, 10:18 PM

Hi! Check out this...

http://www.peakelec.co.uk/atlas.htm

I have found this tool helpful...and a great help when you do not find the datasheet.

Arne K
NORWAY

Samuel Jayaraj · 3rd January 2003, 11:04 AM

I am yet to come across a BC546 in TO92 pack with a different pinout, from any manufacturer. As pointed out earlier, both the PCB layout and the data sheet are indeed correct. The data sheet shows the bottom view of the transistor with the flat side of the package facing you.

dine1967 · 3rd January 2003, 12:39 PM

thanks everybody. I finally figured that out after looking at the datasheet. It was a bit confusing. I must say that its been a pleasure to visit this fourm and a great place to learn. thanks again.

2nd January 2003, 01:23 PM	#1
dine1967 diyAudio Member Join Date: Jan 2003 Location: NJ	P3A amp - BC546 Placement Folks, Happy New Year Iam in the process of assembling a P3a amp. The layout on the PCB suggest that the transistor pins are arranged (looking in the front of device from left to right) as collector , base and emitter. I checked this a number of times to make sure.... hope iam correct. However, the datasheet for BC546 (philips) suggest that the transistor pins as emitter , base and collector for the TO-92 package. Iam a bit confused on the transistor placement.Is the transistor to be placed by turning it around? thanks in advance

2nd January 2003, 02:48 PM	#2
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	sam9 It is quite possible. The NTE cross reference guide cautions on this. Appearentlt the leads are not consistent between manufacturers for some TO-92 types. Having stumbled on to this in the context of PCB layout software, I always double check the lead configuration of the device vs. the PCB pattern.

2nd January 2003, 03:26 PM	#4
carlmart diyAudio Member Join Date: Mar 2001 Location: Brazil	BC546 Looking at an old Cricklewood catalog that I have, that usually served me to identify transistors, if you lie down the transistor, with flat face up and pins toward you, what you have is: collector-base-emitter From left to right. Don't you have a multimeter to test that? In any case it should be better for you to match input tansistors for same Beta. Carlos

2nd January 2003, 09:09 PM	#5
MikeW diyAudio Member Join Date: Sep 2002 Location: North of Boston	Use the data sheet for the transistors you have and match up the correct pins. They may or may not match the board. Good luck. __________________ MikeW

3rd January 2003, 11:04 AM	#9
Samuel Jayaraj diyAudio Member Join Date: May 2001 Location: Bangalore, India	I am yet to come across a BC546 in TO92 pack with a different pinout, from any manufacturer. As pointed out earlier, both the PCB layout and the data sheet are indeed correct. The data sheet shows the bottom view of the transistor with the flat side of the package facing you. __________________ Sam


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2nd January 2003, 03:15 PM	#3
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	Yes, be very careful. I ran into this problem also.

2nd January 2003, 09:31 PM	#6
Rory Christ diyAudio Member Join Date: Oct 2002 Location: Milwaukee, WI	Both the PCB and the data sheet are correct. The data sheet shows the pins from the BOTTOM of the device rather than the top. Once you look at it from this perspective, it all makes sense. Confusing? You bet! I am referencing the following: http://www-us.semiconductors.philips...C546_547_3.pdf I only realized this after I installed all my transistors backwards because I incorrectly assumed the diagram in the data sheet was a top view.

2nd January 2003, 09:33 PM	#7
OliverD diyAudio Member Join Date: Nov 2002 Location: Germany	One thing worth mentioning is that a circuit can possibly work even if C and E of some or all transistors are swapped. I had this problem several times - why do two amplifiers built on the same PCB, wired with the same cable, housed in the same chassis sound and perform so different? Took me days to figure out :-) I don't know a way of finding out whether pinout is E B C or C B E with a multimeter... B C E would be easy, but...

3rd January 2003, 12:39 PM	#10
dine1967 diyAudio Member Join Date: Jan 2003 Location: NJ	thanks everybody. I finally figured that out after looking at the datasheet. It was a bit confusing. I must say that its been a pleasure to visit this fourm and a great place to learn. thanks again.

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