Transistor substitution
Below iv compiled a table of possible substitutes for the original driver & output transistors. Im unable to find all the originals so i have to substitute. Can anyone please comment on which are most suitable for the purpose, the values are for the most part comparable, although different test values. ie voltage, were used in some cases.
Also some drivers & outputs are classified as either low-frequency power amp,general purpose or small signal? Are they all suitable? Also can you find 'low noise' transistors with similar properties as those below? Cheers
Below iv compiled a table of possible substitutes for the original driver & output transistors. Im unable to find all the originals so i have to substitute. Can anyone please comment on which are most suitable for the purpose, the values are for the most part comparable, although different test values. ie voltage, were used in some cases.
Also some drivers & outputs are classified as either low-frequency power amp,general purpose or small signal? Are they all suitable? Also can you find 'low noise' transistors with similar properties as those below? Cheers
It's always difficult suggesting without knowing what is locally available.
You also need the PNP equivalents too.
How about TIP41C and TIP42C (Must be C version... 100volt rating) which are old old favourites.
For the drivers, perhaps BD139 and BD140 or MJE340 and MJE350
Make sure you order new insulating kits too.
Forget the vague descriptions, low power signal etc... they are pretty meaningless.
Noise doesn't even figure here
You also need the PNP equivalents too.
How about TIP41C and TIP42C (Must be C version... 100volt rating) which are old old favourites.
For the drivers, perhaps BD139 and BD140 or MJE340 and MJE350
Make sure you order new insulating kits too.
Forget the vague descriptions, low power signal etc... they are pretty meaningless.
Noise doesn't even figure here
I can get the original 2SD525&2SB595, but the Tip41X & BD243 are both 65W with very similar specs. These seem like a better option?
The BD139&140 & mje340 are rated quite a bit stronger than the originals, that cant be a bad thing i suppose..
Sorry, what do you mean by insulating kits?
Is in circuit oscillation an issue when using slower/faster transistors? how much faster/slower would they have to be?
The BD139&140 & mje340 are rated quite a bit stronger than the originals, that cant be a bad thing i suppose..
Sorry, what do you mean by insulating kits?
Is in circuit oscillation an issue when using slower/faster transistors? how much faster/slower would they have to be?
If you can get the originals I would probably stick with them just for the sake of keeping the whole amp "original"
Or mirror what you do on the good channel.
Are the drivers actually faulty ? have you measured them.
Oscillation won't be an issue. The HF response of the amp is determined by the other components and circuit design.
Insulating kits are the mica/silicon washers and plastic bushes used to insulate the tab of the transistor from the heatsink... I would use the new grease free silicon one and clean any old gunge of the heatsink with meths or iso.
Or mirror what you do on the good channel.
Are the drivers actually faulty ? have you measured them.
Oscillation won't be an issue. The HF response of the amp is determined by the other components and circuit design.
Insulating kits are the mica/silicon washers and plastic bushes used to insulate the tab of the transistor from the heatsink... I would use the new grease free silicon one and clean any old gunge of the heatsink with meths or iso.
Does it matter what combination of driver / output i select? Obviously whichever type selected must be a npn/pnp pair, but as far as those transistors discussed above, it doesnt matter?
Also the 0.47ohm ceramic resistors, these are easily replaced with round type carbon film resistors of the same specs?
Im buying all these replacements without testing because my meters on the way to pickup the components, which is far out of the way from where i stay...
Also the 0.47ohm ceramic resistors, these are easily replaced with round type carbon film resistors of the same specs?
Im buying all these replacements without testing because my meters on the way to pickup the components, which is far out of the way from where i stay...
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The circuit should work OK with "any" combination. Would I do it if it were mine... no even though it works I would want it done correctly...
The pairs given are "complementary" meaning the NPN's characteristics match the PNP's... although in practice they are very different. They come closer than unmatched types though.
The 0.47 ohms. Can you get 0.47 ohm carbon ? Not a "normal" item. I would get a couple of 330 ohms (driver emitter resistors) just in case.
Do you not know what transistors are available until you get there.
even though it works I would want it done correctly... The pairs given are "complementary" meaning the NPN's characteristics match the PNP's... although in practice they are very different. They come closer than unmatched types though.
The 0.47 ohms. Can you get 0.47 ohm carbon ? Not a "normal" item. I would get a couple of 330 ohms (driver emitter resistors) just in case.
Do you not know what transistors are available until you get there.
Yup, just as stated at start of thread, the fault lies with a power transistor, Q19 to be precise. All other drivers & outputs as well as 0.47 resistors appear fine, but Q19 shows short from B - E.. Im going to replace the 2SB595s&2SD525's with BD243C'S&BD244C'S, and the drivers with BC639'S&BC640's as suggested earlier, as well as the 0.47 with new 'cement/ceramics'.
One question about mounting, Do you apply heat sink compound on both sides of the rubber washer behind the transistor tab for better heat dissipation?
One question about mounting, Do you apply heat sink compound on both sides of the rubber washer behind the transistor tab for better heat dissipation?
A lot of the new "rubber" ? or silicon washers are meant to be used dry. You would have to check what type they are... but yes, compound on both sides. If you are not sure apply anyway, won't do any harm. Don't over tighten the power devices down, and check on ohms that there is no continuity from the tab to the heatsink.
And don't just switch on... use the bulb tester first to help save damage if there is any further problem.
And don't just switch on... use the bulb tester first to help save damage if there is any further problem.
Yeah the light bulb in series has already saved my multimeter from careless probe jabbing... Ive replaced the damaged output transistor with same type, and that channel (left) measures the correct reference voltages all over.. The right channel however measures wandering voltages all over, is this AC?! The two orange 34.5V leads from the secondary are fine.
Ive only changed that one transistor so will replace all driver & outputs to see if its one of them..
Or else its a capacitor? Why is the left channel shown in bold linetype on that schematic?
Thanks Mooly
Ive only changed that one transistor so will replace all driver & outputs to see if its one of them..
Or else its a capacitor? Why is the left channel shown in bold linetype on that schematic?
Thanks Mooly
Cheers gents, tested with speakers just now and the left channel (the stable reference voltage channel) is the one humming.. When i touch the volume dial it hums much louder so prob an earth prob as jim suggested cos pcb not screwed back on properly.
I re-tested the right channel and the reference voltages where pretty close what they should be, though they wander a bit, which the L channel doesnt
The light bulb dimly lights only on startup as the caps charge up, after that its complete off, except for when you stupidly short components... Think il replace all driver/output transistors now, let you know what happens
I re-tested the right channel and the reference voltages where pretty close what they should be, though they wander a bit, which the L channel doesnt
The light bulb dimly lights only on startup as the caps charge up, after that its complete off, except for when you stupidly short components... Think il replace all driver/output transistors now, let you know what happens
Ive replaced all driver / output transistors to be sure they werent the fault, however iv just noticed something disturbing, the driver trans were all soldered the wrong way.. Not sure if this amp was repaired before but this doesnt look right. The circuit board has a 'from above' symbol of a T092 with the cutaway & a dot, i imagine the trans is supposed to go on the board like that, with emitter on left and base on right?
If any transistor were fitted wrongly the amp (channel) would never work at all.
Check the pinouts here for the devices you have fitted,
Datasheet catalog for integrated circuits, diodes, triacs, and other semiconductors, view
just type the device number into the blank box and download the data sheets
and fit accordingly.
Look at the print on the PCB to see which is C B & E and then fit the parts. Parts are not always standard, just because they share the same package... always check for yourself.
Do you know which leg is which on the circuit ?
Your confusing things by referring to left and right channels just concentrate on one channel and get that working.
Does either channel work normally and play music ?
Check the pinouts here for the devices you have fitted,
Datasheet catalog for integrated circuits, diodes, triacs, and other semiconductors, view
just type the device number into the blank box and download the data sheets
and fit accordingly.
Look at the print on the PCB to see which is C B & E and then fit the parts. Parts are not always standard, just because they share the same package... always check for yourself.
Do you know which leg is which on the circuit ?
Your confusing things by referring to left and right channels
just concentrate on one channel and get that working.Does either channel work normally and play music ?
Sorry i should have just checked that logically.. The drivers are fitted correctly but the pcb printing show they should be other way round.. The rest of the trans on the board correspond to markings... very strange..
The right channel plays music softly with a hum, the left pops loudly & causes big current draw seen through the light bulb..
A question on the diodes then, the zener in the preamp section shows -18V at its anode, but negligible volts at its cathode, are zeners supposed to show same volts at both ends?
The rectifier diodes measure 0 ohm one way, and open circuit the other.. Is this normal?
The voltages on the right (popping) channel seem close to the left, just more unstable, varying slightly...
Ive tapped all components with insulator and only the zener in preamp made an intermittent difference..
If not a zener, do you think this could be a capacitor?
The right channel plays music softly with a hum, the left pops loudly & causes big current draw seen through the light bulb..
A question on the diodes then, the zener in the preamp section shows -18V at its anode, but negligible volts at its cathode, are zeners supposed to show same volts at both ends?
The rectifier diodes measure 0 ohm one way, and open circuit the other.. Is this normal?
The voltages on the right (popping) channel seem close to the left, just more unstable, varying slightly...
Ive tapped all components with insulator and only the zener in preamp made an intermittent difference..
If not a zener, do you think this could be a capacitor?
Hi colin kenwood/trio used differant driver transistors during the production. Possably because a shortage the 2SA850/2SC1735
and if my memory serves me right the allternative transisters were fitted the opposite way round as mooly quite rightly says the amplifer would not have worked at all if the transisters were fitted the wrong way by another repairer.
regards jim
and if my memory serves me right the allternative transisters were fitted the opposite way round as mooly quite rightly says the amplifer would not have worked at all if the transisters were fitted the wrong way by another repairer.
regards jim
You are going to struggle with this, I can tell... and it's getting late here.
If you are going to fix this at all you are going to have to follow instructions really carefully... and even then there are no guarantees.
It has to be worked through very methodically measuring all the way.
If you are prepared to give that a go on the forum here... we can give it a try.
It will mean fixing (trying to fix
) one channel at a time... and to be sure we would "disable" the channel not being worked on.Up to you if you want to give it a go... and no guarantees
What also worries me is that you seem to have an intermitent connection somewhere ,as you say you can tap parts and the fault alters.
And zeners... normally you should be able to measure the voltage across the diode and that should correspond to the value of the device.
The initial excitement of having new transistors and being 99% theyd fix this has slowly faded... But im up for this challenge, i really want/need this amp to work!I appreciate the ongoing advise i really do... methodical it shall be..
iv remeasured all reference voltages and the L channel shows stable voltages close to what they ought to be, the exception being the 0V by the 0.47ohm resistors which measures around 30-50mA.. I this a prob?
The R channel now is completely unstable, the only transistors with constant voltages are Q8 & Q10, the rest fluctuate at base, collector & emitter..
The supply voltages are stable so it must be caps/resistors in the pre/main amp?
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