Transistors replacement to repair a vintage SS amp

Hello!
I'm trying to fix a vintage SS guitar amp that has a very bad distorsion.
It's a try and guess so i'm replacing transistors... but some are hard to find, would someone know about good replacements ?

MPSA55 (only available at one store with heavy shipping cost)
MPSU06 (this one is fried so i need a new one...)
BD507
SSC PLZ 417 (looks like a diode, cannot find anything related?)
BF315
BC209B


thanks !
 
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I would replace the capacitors before swapping transistors. Capacitors are known to go bad with heat and age. Have you done any troubleshooting? What makes you think it’s the transistors? I think you may end up doing more harm than good by your approach. I’m sure someone with more knowledge that me could help you do some troubleshooting. Good luck.
 
1) this thread should be moved to Musical Instrument Amplifiers

2) which amplifier are we talking about?
Brand and Model please.

3) replacing parts at random with no troubleshooting leads to disaster.

Tell us something about your amp, symptoms, etc. and we might suggest something in return.

4) what Country are you in?= Suggestions are strongly tied to location.
 
What country are you in?
MPSA56 is better than MPSA55, higher Vceo, is available everywhere (newark, digikey, mouser). Moto only made MPSA55 when the fab had a bad day, or some ninny purchasing agent wanted $1 off the 10000 quantity price.
MPSU06 has a weird pinout. Datasheets are no longer available, but I've found them in Allen organ S100 amp. The alldata sheet is a big lie showing picture of MPSW06 which is not the same pinout. A mje340 should handle the power but you have to figure out the pinout and twist the legs around.
I'll leave the european numbers up to Europeans.
2nd the advice of royxc, ELECTROLYTIC capacitors are time fuses designed to make you buy a new amp in however many years the marketing department picked as their price point. I like the 10000 hour service life replacements, so I don't have to do this 4 times like on my ST70 amp. Often they short, and can take out resistors, fuses, even transistors & diodes.
Diodes from 60-s 70-s equipment are either silicon or zener. If followed by an electrolytic cap, you need a schematic to pick the replacement zener voltage & wattage. Zeners have the line connected to the plus of the cap, rectifiers have the not-line connected to the plus of the cap. If generic silicon, try any 3 amp >200 PIV silicon diode in stock at your distributor. You might get away with 1n4004 but they are 1 amp rated.
I replace transistors only if they fail the double diode test or leak too much current with 12 v C to E (-12 for PNP) . Big symptom, the collector of a common emitter circuit is not between 1/3 & 2/3 of the rail voltage. Warning to newbies, when working with power on, no jewelry on hands nor neck, 1 v through a ring can burn your flesh to charcoal. Touch circuit with one hand at a time, current above 25 v across your heart can stop it. Wear safety glasses, parts sometimes explode.
 
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Thanks for your answers!
i'm in france.
Amp is a "musique industrie 915 traffic". schematics are nowhere to be found.
I build and repair tube amps but i'm have very few knowledge regarding SS amps.
I already changed all electrolytics caps (signal caps and filtering caps)
Also replaced all solid caps.
Looked for cold joints, broken leads, etc...

Tried to make a schematics but the pcb is so busy it's a pain to trace...
disconnected the preamp boards from the power amp and sending signal straight to the PA, output is distorted so i know the PA has something wrong
Testing components, i found a dead BC109B (this one was use as a diode ? B and C being tied together) and i accidentaly fried the so hard to replace MPSU06 with a probe slip :/
I tested all the transistors, they test good on my cheap chinese TC1 transistor tester... but sound is awfull.So my last hope is to try and replace the transistors...
The power section use 4 2N3055 with 2 2N3055 drivers . Each section has a 0,25R resistor. I get 20mA in one, 4mA in the other. Something's wrong !
 
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Well, the 20 ma emitter resistor idle current (no AC input) is fine, but you may later want to increase the 4 ma. there is some device to make the bases of the drivers about 1.2 v apart, either a double diode, a resistor, a small transistor connected to the heatsink, something. You would do something to the circuit to increase the 1.2 v (or 1.1, or 1.3) a little. Hopefully the bias circuit collapses the voltage a little as the output transistor heat sink heats up, to prevent thermal runaway.
It helps to listen to the circuit, especially in the preamp, to find out where the distortion starts. could be the input pot. In front of your other amp make a sound probe, which limits the current AC & DC into the other amp input. from your + probe and ground probe, put a 47 k resistor in each. Follow each with a .047 uf >200 v cap. .1 uf will work. Connect the output of the two caps with red LEDs line to not line, or 2.1 v zeners. One side of the two LED's is the hot to the amp, the other side is the ground. Connect the input ground to the preamp analog ground. Connect the hot with a clip lead or something to various points like transistor collectors, to see where the bad sound starts. Clipping is normal, learn to detect that with your ear, obviously signals bigger than 1.2 v will clip.
So pay attention to the stage where the sound is first bad.
 
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Well, the 20 ma emitter resistor idle current (no AC input) is fine, but you may later want to increase the 4 ma. there is some device to make the bases of the drivers about 1.2 v apart, either a double diode, a resistor, a small transistor connected to the heatsink, something. You would do something to the circuit to increase the 1.2 v (or 1.1, or 1.3) a little. Hopefully the bias circuit collapses the voltage a little as the output transistor heat sink heats up, to prevent thermal runaway.
It helps to listen to the circuit, especially in the preamp, to find out where the distortion starts. could be the input pot. In front of your other amp make a sound probe, which limits the current AC & DC into the other amp input. from your + probe and ground probe, put a 47 k resistor in each. Follow each with a .047 uf >200 v cap. .1 uf will work. Connect the output of the two caps with red LEDs line to not line, or 2.1 v zeners. One side of the two LED's is the hot to the amp, the other side is the ground. Connect the input ground to the preamp analog ground. Connect the hot with a clip lead or something to various points like transistor collectors, to see where the bad sound starts. Clipping is normal, learn to detect that with your ear, obviously signals bigger than 1.2 v will clip.
So pay attention to the stage where the sound is first bad.
thanks,
but i need to replace the MPSU06 first to go on testing...
and yes, i need to build that probe :)
 
thanks,
but i need to replace the MPSU06 first to go on testing...
In Europe a BD139 may be easier to find than a MJE340, but they are kind of light on power handling ability. Determine the collector resistor size, the rail voltage, and using 1/2 the rail voltage, calculate I*V across the MPSU06. If wattage greater than 4, you might have a problem. A heat sink would help.
You still have to figure out the input (base) output (collector usually) and ground pin (usually emitter) by looking at the board. Then twist the pins around.
 
In Europe a BD139 may be easier to find than a MJE340, but they are kind of light on power handling ability. Determine the collector resistor size, the rail voltage, and using 1/2 the rail voltage, calculate I*V across the MPSU06. If wattage greater than 4, you might have a problem. A heat sink would help.
You still have to figure out the input (base) output (collector usually) and ground pin (usually emitter) by looking at the board. Then twist the pins around.
Collector resistor seem to be a 4,7k
i have +50 and -50V
so I=50/4,7 = 10mA = 0,01A

P = 50x0,01= 0,5W ?
 
If you like the sound of that amp, i'd suggest youy replace only the fried transistor and only with the same type! .
MPSU06 is NOT AVAILABLE!!! A lot of them blew up, Motorola quit making them.
Of course you can buy a counterfeit any number on ebay/alibaba . Which is probably not even a transistor, just silicon in a TO92 case. Just replaced 21 counterfeit transistors supplied on a new PC by a clueless service dept at an organ supplier. The numbers match! The board tries to make the shutters close & open, fast & slow, all at the same time. The old board had a hole burned in it, no going back.
Nasdak, check voltage between bases of drivers on the two channels. The voltage on the good sounding channel is right. The voltage on the "no idle bias current" is wrong. Maybe a bias diode is shorted or a pot wiper has lost contact. Of course, OT's could still be leaking, or driver transistors.
 
Replacing random transistors is not a good idea.
You have to identify which transistor is not working - amplify.
If you short-circuit the base and emitter the voltage (VDC) in the collector should increase because you are canceling the base emitting diode. If it increases, it is OK, if it does not, the transistor is defective.
Be careful with the correct identification of the TR, if it is a PNP or an NPN.

https://www.diyaudio.com/forums/newreply.php?do=postreply&t=347917

And what exactly is E, B, and C

Find a link in English if you can't translate it,

("how to identify a defective transistor or something like that")
 

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" ¡necesito algo para el BD507, BF315 y BC209B! "


I have searched my TR manual for 1975.
It was a famous manual here, by the authors Algarra-Rodriguez.
It contains TR manufactured until that year with the equivalences between TR of USA, Europe and Japan.

There are none of those transistors!
 
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so, the MPSU06 has been changed for a MJE340 with a little pin bending
Amp is back to previous state : working but very high distorsion ; one 0.25R gets 20ma, the other gets nothing...

You don't have an audio generator and an oscilloscope?
The method is to inject audio signal from the circuit input to the output and observe what happens at the output of each TR
 
Seems that the BD507 could be replaced by a BD139. BF315 seems to be a low power PNP. You might be able to use a BC557 for that. The BC209 could be replaced by a BC549B.

Whenever you try to troubleshoot by replacing transistors it is worth removing all of them and checking them individually. That would also allow you to test parts of the PCB without the devices shunting resistors etc.

Not sure about replacing the MPSU06 with an MJE340 - the frequency response of the latter is not spec'd and could well be slower than the U06, which may cause problems.

BD139 might not quite manage +/- 50V rails. It is rated at 100V BVcbo, but that assumes reverse/zero bias on the base. And as Mullard/Philips do not seem to make it others have only spec'd this at 80V BVcbo/BVCeo. Something like a 2SC2911 would be better for a low power stage (VAS perhaps, rated 160V but only 140mA) but a driver device may need a TO-220, although a BD139 should work in class AB driver where its base is reverse biased in the off state. And C2911 seems to be hard to find, but there may be other similar devices.

Can't help any more without knowing what the circuit is.
 
The power section use 4 2N3055 with 2 2N3055 drivers . Each section has a 0,25R resistor. I get 20mA in one, 4mA in the other. Something's wrong !

Collector resistor seem to be a 4,7k
i have +50 and -50V
so I=50/4,7 = 10mA = 0,01A

P = 50x0,01= 0,5W ?

+/-50 volts with 3055’s? That’s a bit iffy. Especially using them for drivers, where leakage gets multiplied by the output transistor gain. They seem to be mismatched (also bad) so you might end up changing them out for MJ15015 which is a higher voltage 3055.

Half a watt in the U06? Also not a good idea. The U06 is an A06 on a bigger leadframe, but it’s still a dinky small-signal transistor. That’s why a lot of them blew out - trying to get too much blood out of a stone. It’s pretty usual practice to replace those old MPSU’s with MJE243/253 or 340/350, depending on the operating voltage.