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do output transistors have to match ?

D

donberry

Super Member
Bose 1801 resto - almost done except the output transistors on one board bit the dust when the diode gave up the ghost.
Obviously do not make those anymore.
Question - do I have to replace all of the ones on the other board now to match them ? Mainly asking as there are 14 per board.
I am obviously pretty ignorant, but if i did not replace the ones on the good board, are the 2 channels going to sound the same ?
Yes, i am that ignorant .
 
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Depends. On both. There are measurable differences between devices and therefore IMHO, they could sound different. Is this an Emitter follower, Complementary feedback, type output design? What were the original number on the outputs?
 
the original ones were the 2N5840, which is in mine. Bose then replaced those with the MJ15011. Mouser has the MJ15011 - cost about $4.50 a piece and I have 14 per board.
I did just find some on ebay that I do not believe are counterfeit, supposedly NOS, NOT from Hong Kong that are under $3.00 a piece so am checking to see if he has 28 of them.

I guess after doing all of this resto, it would be kind of ridiculous for me to not match them. I was thinking it was something i could do later, but I just need to quit being in a hurry and do it right.
Was hoping to get the new binding posts and filter caps, but now will just hold off until nest month on those.
 
I have 19 of them. Give me your address and I'll send them to you, you can have them, They did not do well in a PL400.
 
I sent u an email. as mentioned tho, is too generous and will have to give you something for them. Just would not feel right karma wise.
 
laatsch55 said:
I have 19 of them. Give me your address and I'll send them to you, you can have them, They did not do well in a PL400.
Click to expand...

Your a real peach of a guy..Bravo..:thmbsp:

OP Don't buy the Onsemi's on Ebay...
 
laatsch55 said:
I have 19 of them. Give me your address and I'll send them to you, you can have them, They did not do well in a PL400.
Click to expand...

Now that's some great Karma-osity! Good Karma + generosity = Yes, Karma-osity:yes:

OK, didn't sound as funny the second time I read it. Either way, that's a very generous offer. This site's members never cease to amaze me in the offer of helping hands as we travel our various audio paths.

laatsch55, very generous and helpful indeed!
 
Leach's matching circuit was intended for matching small signal transistors, not output transistors. It might not be suitable. Also, I would want to know whether bose (non-capitalization intentional) matched the originals and to what extent. It might not be necessary.
 
I think it would reduce the distortion if the output transistors were matched.

I am guessing they were at least roughly matched by the OEM.
 
They should be matched to reduce the opportunity for current hogging.

Current hogging causes the output transistors with the highest gain to dissipate more power than the transistors with lower gain, thus reducing the aggregate power-handling capability of the amplifier.

If you buy the transistors from Mouser, they will automatically be fairly well matched.

Fred
repairing audio gear since 1972

* * * * *
 
Fred:
Are you saying that Mouser matches the transistors when they are ordered in quantity? I find it hard to believe that a mass distributor like Mouser or any other would have the resources and available labor to do this without charging for it. It wouldn't be economically feasible otherwise. I would expect possible variations within the manufacturer's broad spec limits in any shipment from any vendor unless they are specified otherwise, and that has always been my experience. Maybe you are just lucky?
Also, the low value emitter resistors (and in some cases, base resistors) connected to each output transistor tend to equalize current sharing. While it is in general beneficial to match transistors, it is not always necessary and many if not most designs do just fine without doing this.
 
Mouser Matching...

Yep Bubba, this one looks just like that one..Hand me one of those shiny foil bags..
 
If you buy a bunch of transistors they will likely be from the same lot and therefore be fairly close. I check the voltage drop across emitter resistors to verify current sharing.
 
To answer 2chanman's question --

When I buy transistors from Mouser or Digi-Key, I will usually get devices that were manufactured on a single production run. There are often codes stamped on the transistor bodies to verify this.

Transistors from the same production run usually have closely matched gains, normally within about 10%.

When I buy transistors from small suppliers, I will often get devices from different production runs, and these will often have divergent gains. Also, more and more, from small distributors, I am finding transistors that are either "culls" or counterfeits.

Here are some output transistors that really "kick ass" --

http://www.datasheetcatalog.org/datasheet/on_semiconductor/MJ21193-D.PDF

Fred
repairing audio gear since 1972

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(note - its been a while) When Bose first introduced the 1800, one of their problems was that they had such high requirements for matching transistors that it was holding up their production and kept the price high. I imagine QC and production standards are higher now, but would still try and get as close a match as possible with groups of parallel devices. I don't have a schematic, but the general rule of thumb is that the lower the emitter resistors, the closer the matching should be. The Phase Linear manuals had procedures for checking current sharing by comparing drops in the emitter resistors, and any amp with parallel outputs should be tested similarly. My $.02
Steve
 
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