:Help: Are these transistors interchangeable?

[tarnationsauce]

Just wondering if you guys think these two transistors are close enough to be compatible?

2SB1186A
http://pdf.alldatasheet.com/datasheet-pdf/view/88108/ROHM/2SB1186A.html

KTA1024
http://pdf.alldatasheet.com/datasheet-pdf/view/69643/KEC/KTA1024.html

They are part of an amplifier's driver circuit. It originally had the KTA1024, but it fried. And I have a few 2SB1186A's on hand.
I know the datasheet for the 1186A doesn't show pinout, but it's the same as the KTA1024.
I think they are close enough, but I'm no transistor expert and want a 2nd opinion.

 

[destroyer X]

Tarnationsauce, they are not perfectly compatible.

One of them have a very nice small capacitance...but a very small colector to emitter current.... this one is the KEC.

The Other one has enormous capacitance, and a very good colector to emitter current.

Removing the KEC and placing the other will be better than the oposite....this will depend of your application.

I do not think they are perfect substituted one for the other...only in very special cases of very low current applications.

Those transistors are not made to audio applications they are more adequated to power supply switching purposes.

Yes, they can work to audio, as one of them are already working, but some guys have the idea that the audio produced is not so good as can be when using standard BJTs, custom made for audio frequencies.

If you decide to replace, please inform the result.... as i have some doubts....lets listen other guys in advance.

nanabrother@yahoo.com

regards,

Carlos

 

[tarnationsauce]

Yeah, I notice 4-5pf vs 30pf is a pretty big difference.
This will be for low current application for voltage control.

I think I'm going to try it replacing the KTA1024 with th B1186A . I'll report back.

 

[destroyer X]

Yeah!...in your case, it will work!

But tell me some, after replacement.

There are always something to learn...will work...but i will be happy to listen if you could perceive some advantage or the opposite.

regards,

Carlos

 

[tarnationsauce]

I replaced the transistor and the amplifier plays audio, but buzzes then goes into protection mode.
So I either have something else wrong. Or something about this transistor makes it incompatible.

 

[anatech]

Check to see if you are now a radio station.

-Chris

 

[tarnationsauce]

Check to see if you are now a radio station.

-Chris

I forgot to mention that this is a high power audio amplifier.

 

[anatech]

RF. You have an AF amp. Is it now an RF amp also? (Oscillation)
-Chris

 

[DUG]

A better choice would be a 2SA1124

get the data sheet through Digi-key and compare.

ft is higher but the rest is very similar

 

[tarnationsauce]

RF. You have an AF amp. Is it now an RF amp also? (Oscillation)
-Chris

Lol, sorry I misunderstood your question.
Actually, yes! Just about .5 seconds before it shuts down it oscillates. It sounds like it's about 60Hz. I have a scope at my disposal, should I take a reading of it? Is there a way to stop it? And how did you know that was a possibility? Was it the high Cob of the b1186a?
also, is your avatar a quote form That 70's Show? 😀

A better choice would be a 2SA1124

get the data sheet through Digi-key and compare.

ft is higher but the rest is very similar

Yeah that does seem like a good replacement, except the hFE is quite a bit higher too. Doesn't that mean it has more gain? A higher ft shouldn't effect anything I don't think.

Thanks, everybody for your help so far.

 

[Eva]

2SB1186A is not a good replacement at all.

There are some standard models that should fit your needs, though:

2N5401 (TO-92)

MPSA93 or MPSA92 (TO-92)
MPSW93 or MPSW92 (same as previous but in a big TO-92 case rated at 1W)

BF422 or BF420 (TO-92)
BF472 or BF470 (same as previous but with TO-126 case)
BF872 or BF870 (same as previous but with Philips propietary case)

Be careful with pinouts 🙂

 

[tarnationsauce]

Thanks, Eva. I'm going to look into those transistors.

However, I replaced the transistor from one from a working channel of the amp. And it still is distorted andshuts down. So my problem is somewhere else. But I checked every component except the caps. But usually caps dont fry when a transistor's junction melts. I suppose maybe it could be an opamp. 🙁

 

[tarnationsauce]

Alright. I hooked the output to an o-scope. It plays really distorted audio, then ramps up to +20vdc, then 60hz oscillation. Then the amp turns off.
I have a feeling the problem is in the preamp circuit. Because the power amp's rail voltage is quite a bit higher than 20v. But the preamp/protection circuit appears to run off +/- 15v.

 

[anatech]

Hi tarnationsauce,
It sounds like you may have other problems there. Can you post a schematic or at least a make and model (in case I missed it).
-Chris

 

[tarnationsauce]

Hi tarnationsauce,
It sounds like you may have other problems there. Can you post a schematic or at least a make and model (in case I missed it).
-Chris

Chris, My amp is an Alesis RA500. I looked high and low for a schematic. On Alesis's website they claim the amp is "non-servicable" and must be repaired by Alesis. So I'm sure they're going to be unwilling to give schematics.

The good thing about the amp is it's extremely modular. The PSU / power amp / preamp& protect are all on seperate boards. But to remove the preamp from the power amp would be pretty hard as it's soldered/glued into place.

It uses three each, 2sc5200 / 2sa1943 with one c4793 / a18c7 drivers respectively.

When the transistors blew, the 5w/ .22 ohm Emitter resistors blew. I replaced them with .25 ohm resistors as I couldn't find 5w .22 ohm resistors any where. But I doubt that affects the amp this way.
THere are 2 original power transistors (2sc5200) that survived, but maybe they are bad but read good on a meter. My next test is to borrow 2 known good transistors from the working channel.

All in all this is a verry simple design and it's frusterating thateverything checks good, but it don't function properly.

Anybody know a good way to test zeners PIV without building a test circuit? All my zeners forward voltages read good ~.53v

 

[tarnationsauce]

BTW I forgot to mention the KTA1024 is one of the differential input transistors.

 

[anatech]

Hi tarnationsauce,

Okay, I couldn't find where they say it can't be serviced. I did find a description that gives you an idea of what the circuits generally look like.

Replace all outputs with new. Do not use parts from the other channel to find out what's going on. The other channel works, it's important you leave it alone. Without a schematic this is crucial!

-Chris

 

[TonyTecson]

hmm...output trannies survived is a miracle! make sure you get all busted parts found out and replaced before attempting to power up! i would check around the bias circuit up to the input ltp.

 

[tarnationsauce]

2SB1186A is not a good replacement at all.

2N5401 (TO-92)

That transistor worked perfectly, thanks for the recommendation.

Replace all outputs with new. Do not use parts from the other channel to find out what's going on. The other channel works, it's important you leave it alone. Without a schematic this is crucial!

I replaced all the transistors and it still is did the exact same thing.
So I went through and replaced all four of the zeners (1N4148) and voila! It works perfectly now!

Thanks a bunch everybody for helping. 😀

 

[Eva]

It's not desirable to mix different transistor models in differential pairs since that would degrade performance. It would be a good idea to replace the other KTA in case you haven't done it yet.