Transistor Replacement

portlandlay · 11th December 2005, 10:28 PM

I am trying to bring my Sugden A21 (old) amp from the dead to the living.

It looks like one channel is dead and I think that a bad BFY53 transistor is the problem. The rest of the amp and the scematic only show BFY52. Since I am not a transistor guy I need help. I see that BFY52's are available and I want to use one of these instead. It looks like the h(FE) min for the BFY53 is 30 and 60 for the BFY52 otherwise they look very similar.

Is this OK?

anatech · 12th December 2005, 12:00 AM

Hi portlandlay,
I can't find data on the BFY53 so I can't advise. If the only difference is a higher minimum gain, then maybe - yes.

Anyone else have a clue?

-Chris

Original Burnedfingers · 12th December 2005, 12:06 AM

Can you post a schematic of the amp?

portlandlay · 12th December 2005, 12:26 AM

There is no exact shematic. The one under it is very very close to the one found at http://www.tcaas.btinternet.co.uk/index-3.htm then going to Sugden.

I found both the BFY53 and BFY52 specs (not much) at http://www.americanmicrosemi.com/pro...-05-1000.phtml

poobah · 12th December 2005, 12:42 AM

Hey Portland,

Does the other channel of the amp have the same __53 transistor?

Could this be a sloppy repair?

poobah · 12th December 2005, 12:57 AM

Hey Portland,

If the schematic says BFY52 (high hfe) and you found a BFY53 (low hfe) on the board... especially if the other channel on the amp has a '52; the manufacturer may have been measuring 53's and sorting out and using the 52's with high gain... happens all the time.

Anatech is dead on the mark though... usually you can sub an otherwise equivalent transistor with another unit of higher hfe.

Hope this helps,

portlandlay · 12th December 2005, 01:14 AM

Both of the channels have one 53. The schematic differs from this but the shematic was really not the same amp. It was by James Sugden during the time this was made but was different in some small ways from the A21 that I have.

anatech · 12th December 2005, 07:05 PM

Hi portlandlay,
Thanks for the link to the specs. They do appear identical except for the DC current gain.

What position in the 10W schematic is closest to where the BFY53 located in your amp?

-Chris

portlandlay · 12th December 2005, 07:14 PM

anatech,

No, thank you for taking the time to look at it. The 53 is the one that that is left on the schematic. It is not driectly feeding the ouput transistors.

Stephen

anatech · 12th December 2005, 07:19 PM

Hi Stephen,
I read that as TR3, an emitter follower (buffer). The higher gain will reduce the loading on the preceding stage. Go ahead and use the BFY52 instead.

-Chris

11th December 2005, 10:28 PM	#1
portlandlay diyAudio Member Join Date: Dec 2004 Location: Washington State	Transisitor Replacement I am trying to bring my Sugden A21 (old) amp from the dead to the living. It looks like one channel is dead and I think that a bad BFY53 transistor is the problem. The rest of the amp and the scematic only show BFY52. Since I am not a transistor guy I need help. I see that BFY52's are available and I want to use one of these instead. It looks like the h(FE) min for the BFY53 is 30 and 60 for the BFY52 otherwise they look very similar. Is this OK?

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12th December 2005, 12:00 AM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi portlandlay, I can't find data on the BFY53 so I can't advise. If the only difference is a higher minimum gain, then maybe - yes. Anyone else have a clue? -Chris

12th December 2005, 12:06 AM	#3
Original Burnedfingers diyAudio Member Join Date: Nov 2002	Can you post a schematic of the amp?

12th December 2005, 12:26 AM	#4
portlandlay diyAudio Member Join Date: Dec 2004 Location: Washington State	There is no exact shematic. The one under it is very very close to the one found at http://www.tcaas.btinternet.co.uk/index-3.htm then going to Sugden. I found both the BFY53 and BFY52 specs (not much) at http://www.americanmicrosemi.com/pro...-05-1000.phtml

12th December 2005, 12:42 AM	#5
poobah diyAudio Member Join Date: Nov 2005	Hey Portland, Does the other channel of the amp have the same __53 transistor? Could this be a sloppy repair?

12th December 2005, 12:57 AM	#6
poobah diyAudio Member Join Date: Nov 2005	Hey Portland, If the schematic says BFY52 (high hfe) and you found a BFY53 (low hfe) on the board... especially if the other channel on the amp has a '52; the manufacturer may have been measuring 53's and sorting out and using the 52's with high gain... happens all the time. Anatech is dead on the mark though... usually you can sub an otherwise equivalent transistor with another unit of higher hfe. Hope this helps,

12th December 2005, 01:14 AM	#7
portlandlay diyAudio Member Join Date: Dec 2004 Location: Washington State	Both of the channels have one 53. The schematic differs from this but the shematic was really not the same amp. It was by James Sugden during the time this was made but was different in some small ways from the A21 that I have.

12th December 2005, 07:05 PM	#8
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi portlandlay, Thanks for the link to the specs. They do appear identical except for the DC current gain. What position in the 10W schematic is closest to where the BFY53 located in your amp? -Chris

12th December 2005, 07:14 PM	#9
portlandlay diyAudio Member Join Date: Dec 2004 Location: Washington State	anatech, No, thank you for taking the time to look at it. The 53 is the one that that is left on the schematic. It is not driectly feeding the ouput transistors. Stephen

12th December 2005, 07:19 PM	#10
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Stephen, I read that as TR3, an emitter follower (buffer). The higher gain will reduce the loading on the preceding stage. Go ahead and use the BFY52 instead. -Chris

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