Transistor Substitutions

Thanks rottalpha, yes it would be all the 4 (PNP and NPN) replacing trannies. My concern is that a fT of 20MHz (or 25MHz) could cause some stability problems (oscillations) when replaced the original 10MHz ones. Safer to use MJ21193/94 (fT of 4MHz), I guess. It's for an AU-317 II (1980).
 
Is there anybody familiar with Power pack or Power Amplifier STK0050n 10 pins 50w? I found STK0050II wondering it is the same as stk0050n?
Thanks!!
 
Is there anybody familiar with Power pack or Power Amplifier STK0050n 10 pins 50w? I found STK0050II wondering it is the same as stk0050n?
Thanks!!

Chances are what you found are cruddy fakes that will fail after a while, the STK0050's are pretty much unobtanium now since they haven't been in production for over 30 odd years. But yeah I'd imagine they're the same as the 0050II.
 
Hi!

I'm repairing a Metaxas Solitaire III mono bloc that someone plugged in 230V mains when it was configured for 110V. Let's just say it is total carnage in there. I'm having some trouble finding replacements for the power transistors (NEC 2SA1227/2SC2987) and the drivers (NEC 2SA985/2sc2275). For the drivers I was wandering if going for the Onsemi KSA940/KSC2073 would be a good idea (they are a lot slower though : 4Mhz against the original 100Mhz, and have a lower gain : about half).
Thanks !
 
I'm having some trouble finding replacements for the power transistors (NEC 2SA1227/2SC2987) and the drivers (NEC 2SA985/2sc2275). For the drivers I was wandering if going for the Onsemi KSA940/KSC2073 would be a good idea (they are a lot slower though : 4Mhz against the original 100Mhz, and have a lower gain : about half).
Thanks !

2SA1227/2SC2987
Silicon PNP/NPN
Purpose: audio frequency power amp

Pd: 120 W
Vcbo: -+140 V
Vceo: -+140 V
Vebo: -+5 V
Ic: 12 A
ft: 60 MHz
hFE: typical 130

Package: X104-1 or TO-3PFa (this looks like a TO-220 would fit, but I can't tell from just the photo)

Modern contenders for this application, minus those whose specs don't fit the above, are:

Part Vceo Vcbo Vebo Ic (A) Icmax (A) Pd (W) Hfe Package
MJW3281A,MJW1302A 230 230 5 15 25 200 100 TO-247
MJW21194,MJW21193 250 400 5 16 30 200 50 TO-247
MJW21196,MJW21195 250 400 5 16 30 200 50 TO-247
MJE4343,MJE4353 160 160 7 16 20 125 35 TO-247​

To hit the HFE you've had with the original, I think you'd just aim for the MJW3281A,MJW1302A NPN/PNP pair.​

2SA985/2sc2275
Silicon PNP/NPN
Pd: 25 W
Vcbo: -+ 120 V
Vceo: -+ 120 V
Vbeo: -+ 5 V
Ic: 1.5 A
ft: 180 MHz
HFE: MIN: 150
Package: TO220

Your choice of KSA940/KSC2073 seems fine. You may want to look at a "common here on AK" driver pair like the MJE15029G, MJE15031G, MJE15033G, or MJE15035G (these are all PNP parts of a PNP/NPN pair. The datasheet for each will tell you the matching NPN device).
Good luck!
 
Thanks for the info, I think I might indeed go for the MJE15030/15031 as drivers and the MJW3281A/1302A as outputs. Just one concern, won't the big difference in transition frequency and gain be a problem ?
 
Drivers:
Toshiba:

TTA004B
TTC004B

Absolute Maximum Ratings
Characteristics Symbol Rating Unit
Collector Current IC 1.5 A
Collector Current ICP 2.5 A
Collector power dissipation PC 10 W
Collector power dissipation PC 1.5 W
Collector-Base Voltage VCBO 160 V
Collector-emitter voltage VCEO 160 V
Electrical Characteristics
Characteristics Symbol Condition Value Unit
Transition frequency (Typ.) fT - 100 MHz
DC Current Gain hFE (Max) hFE - 280 -
DC Current Gain hFE (Min) hFE - 140 -
Collector Emitter Saturation Voltage (Max) VCE(sat) - 0.5 V
 
Thanks for the info, I think I might indeed go for the MJE15030/15031 as drivers and the MJW3281A/1302A as outputs. Just one concern, won't the big difference in transition frequency and gain be a problem ?

Im a hobbyist, not an E.E. or pro tech, so take anything I suggest and carefully double-check with people who actually know.

That said, yes, you should look for a device that has a simialr or higher hfe gain. The various hfs gain codes (like MJE15030 "E" vs "G") is what you should look at. The gain codes will tell you "when I get these new parts, how much gain will they have".

The ft is a bit different. If I understand ft correctly, it is the frequency at which this device stops working (i.e. Amplifying). Because this is an audio frequency application, you require a ft of at least 20k Hz. Your original part was 60 MHz and the new part is way higher. That means both will amplify your audio frequencies just fine. The _trouble_ would be if your circuit is delivering higher frequencies, i.e. RF, and these newer, higher ft devices would happily amplify them. That's not good as you could get oscillation (motor boating) and the amp will work harder with no audio benefit.

Circuit designs, especially newer ones, have tiny capacitors in an amongst the driver or adjacent stages to act as a low pass filter and cut out any frequencies above 20k Hz (or so). The trouble if you use a newer device with higher ft would be if your circuit IS picking up RF and DOES NOT low-pass filter it.

Now someone with much more experience and knowledge can point out where I'm wrong and give you a better answer. I think your above choices are good ones.
 
Very fast transistors (60MHz) are used because they are more linear in the audio range. This is necessary for fast amps with high slew rate. I'm sure the amp manufacturer would have not specified a 60MHz transistor when a less expensive 4MHz transistor would work. The 60MHz transistor will have less distortion, etc. in the audio range. I would not alter the original design too much by using transistors that are rated 1/15th the speed of the original.

Sanken is still making output transistors that are 50 / 60 MHz..
 
Very fast transistors (60MHz) are used because they are more linear in the audio range. This is necessary for fast amps with high slew rate. I'm sure the amp manufacturer would have not specified a 60MHz transistor when a less expensive 4MHz transistor would work. The 60MHz transistor will have less distortion, etc. in the audio range.

Huh. I guess I have no idea what ft really means. I was under the impression that the zone of linearity of solid state device was a part of its operating characteristics, effectively the equivalent of a tube's same thing. And that this is why you supply it with a particular voltage and pay such careful attention to the bias voltage. So, you're saying the ft directly relates to, influences or governs, whether a device is linear in the audio range? I'd love to actually understand this parameter better.
 
Hi!

I'm repairing a Metaxas Solitaire III mono bloc that someone plugged in 230V mains when it was configured for 110V. Let's just say it is total carnage in there. I'm having some trouble finding replacements for the power transistors (NEC 2SA1227/2SC2987) and the drivers (NEC 2SA985/2sc2275). For the drivers I was wandering if going for the Onsemi KSA940/KSC2073 would be a good idea (they are a lot slower though : 4Mhz against the original 100Mhz, and have a lower gain : about half).
Thanks !
Mjw3281A and 1302A are probably as close as you will find for the outputs.
2SA1930 and 2sc5171are (IMHO) a closer fit for drivers. 2A 200mhz 180 volt parts. Only rated at 20 as opposed to 25 watts.
2sa1859A and 2sc4883a. 2A 60mhz 180 volt parts. Also rated at 20 as opposed to 25 watts.
Depending on the circuit, slow drivers may not work well.
Dimensionally, TO-247 is the squared off version of TO3P, and should be interchangeable.
My 2 cents....
 
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Thanks for your inputs. The 2sa1930/2sc5217 look indeed a great replacement, trouble is they are obsolete as well. Mouser suggests TTA004B/TTC004B as equivalents for this part as did redk9258 above. They are only 1.5W devices, I don't know in which amount the drivers dissipate but that does seem a bit close. I assume they didn't choose 25W devices for no reason when designing the amp.
The Sanken Parts are more expensive then the Mjw3281A and 1302A and there doesn't seem to be that much improvement spec wise to prefer them.
 
This novice needs assistance with a proper transistor substitution. Only the 2SD1200 was shorted next to a blown resistor on the Integra I'm customizing/restoring. Question is, Should I also replace its "complimentary" even though it tests good on the MK328 device?
Screenshot_2018-10-28-07-28-01.png
 
@ dlucy,

I have to admit, I'm no EE. Just a hobbyist. I've read several threads here at AK by people that are very experienced about subbing driver / output transistors. Mark The Fixer for one says slow transistors will cause a Pioneer Non Switching Amp to not work properly. I'm pretty sure I've read similar posts by Echowars.

The slower transistor might work but maybe distortion will no longer be to spec. I don't know. I would not sub a transistor with one 15 times lower fT.
 
Replacing transistors can be a minefield.
I replaced the output transistors in a 1980's Maplin disco amp 225WRMS.
I then got oscillation on the output. I had to put in bigger VAS capacitor to slow things down.
The new transistor had a much higher gain than the originals.
And that was with same number 2N3055/MJ2955 so using different transistors could be troublesome.
By gain do you mean beta/hfe? Why does having a higher beta/hfe represent a problem?
What was the cause of the oscillation? Did the closed loop bandwidth of the amp increase, or did the phase margin decrease?
 
Thanks rottalpha, yes it would be all the 4 (PNP and NPN) replacing trannies. My concern is that a fT of 20MHz (or 25MHz) could cause some stability problems (oscillations) when replaced the original 10MHz ones. Safer to use MJ21193/94 (fT of 4MHz), I guess. It's for an AU-317 II (1980).
Why will replacing a device with an FT of 10MHz with one with an FT of 4MHz be better than replacing it with one of 20MHz. What oscillations are you concerned about?
 
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