MPS8099/MPS8599 vs: BC550C/BC560C - diyAudio
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Old 18th May 2005, 01:01 AM   #1
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Default MPS8099/MPS8599 vs: BC550C/BC560C

How about substituting some MPS8099/MPS8599 transistors for the BC550C/BC560C? The BC devices are proving difficult and/or expensive to source in the small quantity (3 pairs) needed.

However, my trusty parts box has produced 3 pairs of the MPS8099/MPS8599 and they all measure an Hfe of ~200 (with my meter). But the "C" in the BC devices indicate an Hfe range of 420-800. Otherwise most of the specs for the MPS devices are very similar to those of the BC devices.

What do you guys think? Are the MPS8099/MS8599 transistors close enough to use in place of the BC550C/BC560C? I'm not looking for perfection here, just a working amp that sounds good.

Thanks for your help .
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Old 18th May 2005, 01:17 AM   #2
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Hi Dick


You have to ask what is the circuit need for the "C" grade of BC550/560 as the four have similar minimum gains. There may be a reason for Hfe of 420-800 rather than 200. It could be a base bias restriction, or a stability consideration.
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Old 18th May 2005, 01:33 AM   #3
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not a problem should be fine for your application
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Old 18th May 2005, 02:23 AM   #4
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MPSA56/06 too (aren't these the substitutes that Dr. Leach had recommended?)

sometimes the MPS8599 are difficult to latch onto -- they are on 6 week backlog at the moment. MPS8099's can be had anywhere.
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Old 20th May 2005, 08:21 PM   #5
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Thanks to everyone for their comments. I also had an opportunity to confer with a consulting EE (not a member here). We compared Vcbo, Vceo, Vebo, Ft, etc. , and concluded that the MPS and BC devices are very similar with major specs being almost identical -- except for Hfe. He couldn't offer an opinion about the need for high Hfe BC devices when they are used in cascode with MJE340/350 devices. Anyway, he said "go for it" with the caveat the final product be checked with an o'scope for oscillation (a good recommendation for any amp project).

Cheers........
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Old 20th May 2005, 09:10 PM   #6
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Keep in mind the supply rail voltages!
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Old 20th May 2005, 09:10 PM   #7
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MPS8099/MS8599 is similar but with different pinout and much worse current gain, which probably isn't any problem but you may have to change some passive parts.

If you really want BC550C and BC560C I have lot's of them. Send me a message if you want some.
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Old 21st May 2005, 06:36 AM   #8
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The easiest and probably most reliable sources for BC550C and BC560C (or whatever else version) are in my opinion :

Fairchild Direct (just order 100 each and pay by credit card)

or Sample request from On Semi (limited to 25 pieces each, but you can order up to 10 semiconductor types for US$15, again credit card).

Have tried both. Very satisfied customer. And for sure no fakes.


Patrick
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Old 21st May 2005, 03:47 PM   #9
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EUVL,

I considered getting 100 each of the two devices needed and out of the 200 I should be able to extract sufficient number of matched pairs. Then, what do I do with the remainder?

Two hundred transistors at around $0.35@ would cost me $70 US. How much to buy 2 or 3 matched pairs? Do you want to sell me 3 matched pairs, matched at around 10% in the 550 Hfe range? How much for them?

I have gotten samples before but how large a group of devices would I need to extract matched pairs?

I don't disagree with you but so far do not think it is an economical way to get the handful of required parts. I am waiting to hear from Peranders who may have my solution. If he doesn't, perhaps you do?

Thanks.......
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Old 21st May 2005, 04:05 PM   #10
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a) These are so general purpose that you'll always find some use. I must have used 50 out of the 100 by now.

b) 25 samples from On-Semi should probably give you 3 pairs of each type easy. Hfe does vary between complementary pairs so one needs luck, like everyone else. But if you have 10 types of semiconductor to order (power transistors, logic chips, diodes, even regulators, .... ), On Semi is bargain.

c) I do not use them for amplifying (I used MPSA18, also from On Semi), and I do not use complementary, so I have no matched complementary pairs on hand. And I doubt anyone would want to offer complementary pairs for money because it is a lot of work and the items are low value. But maybe peranders or other DIYers can help you with matched pairs.


Patrick
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