It seems some semis are unreliable/shot and possibly the differential pair you replaced earlier on. It can not be the electrolytic caps anymore and it does not seem to be the speaker switch.
It are probably semis and before you know it you are spending weeks of valuable time. You could decide to replace all transistors except power stage, including all Zener diodes and diodes.
BTW some tips for after it has been repaired and you want to max it out:
- Resolder ALL connections. Often forgotten but really advisable with old stuff.
- It would be better to use MUSE 100 µF 16V bipolar electrolytic caps for C05 and C06 as its also AC coming there.
- C01 and C02 can be silver mica or Styroflex, I guess these are ceramic? Same goes for all the other very small value caps.
- C03 and C04 can easily be WIMA MKS2 10 µF 50V types in 5 mm pitch.
- C33, C34, C35 and C36 can easily be replaced for WIMA 4.7 µF 50V MKS2 film caps in 5 mm pitch.
It are probably semis and before you know it you are spending weeks of valuable time. You could decide to replace all transistors except power stage, including all Zener diodes and diodes.
BTW some tips for after it has been repaired and you want to max it out:
- Resolder ALL connections. Often forgotten but really advisable with old stuff.
- It would be better to use MUSE 100 µF 16V bipolar electrolytic caps for C05 and C06 as its also AC coming there.
- C01 and C02 can be silver mica or Styroflex, I guess these are ceramic? Same goes for all the other very small value caps.
- C03 and C04 can easily be WIMA MKS2 10 µF 50V types in 5 mm pitch.
- C33, C34, C35 and C36 can easily be replaced for WIMA 4.7 µF 50V MKS2 film caps in 5 mm pitch.
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These are excellent replacements for old crappy disk type ceramic caps:
https://content.kemet.com/datasheets/KEM_C1058_RADIAL_MOLDED_C0G.pdf
edit: I just read the post below and I of course meant the differential pair in the defective channel. I would however always replace them in the other channel too when the repair is successful. Channel differences are easily heard by many. Semis should be the same brand/type/age in both channels.
https://content.kemet.com/datasheets/KEM_C1058_RADIAL_MOLDED_C0G.pdf
edit: I just read the post below and I of course meant the differential pair in the defective channel. I would however always replace them in the other channel too when the repair is successful. Channel differences are easily heard by many. Semis should be the same brand/type/age in both channels.
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I remember the original thread and can see it was the left channel back then at fault.
The same comments apply now as then... you found there was a recognised issue with the diff pair transistors (a fairly common fault) although my line of initial thinking at the time was to suspect the hot running VAS transistor.
Vintage Toshiba 330 power amp problem, possible repair?
I think you have to go down the same route now. Look at the diff pair on the right channel and then take things from there.
The same comments apply now as then... you found there was a recognised issue with the diff pair transistors (a fairly common fault) although my line of initial thinking at the time was to suspect the hot running VAS transistor.
Vintage Toshiba 330 power amp problem, possible repair?
I think you have to go down the same route now. Look at the diff pair on the right channel and then take things from there.
Thanks for the input Jean-Pauk and Mooley.
I replaced 4 transistors last time, TR1, TR2, TR3 and TR4. Pretty sure that's the diff pair for each channel...
Just a thought but would the flat, disc shaped 4700pf 250V caps on the power switch be worth looking at?
My knowledge of circuits is pretty limited....
I replaced 4 transistors last time, TR1, TR2, TR3 and TR4. Pretty sure that's the diff pair for each channel...
Just a thought but would the flat, disc shaped 4700pf 250V caps on the power switch be worth looking at?
My knowledge of circuits is pretty limited....
Limited is the right word! 
Please think what those caps do when the amp is powered on....
They can not cause the issues the amplifier has. They could cause other issues if they would be defective. I learnt it is better to solve real problems first instead of creating other problems to solve...but that could entirely be my dutch upbringing
I would replace Tr1 to Tr6 and the 18V Zener diode without blinking an eye and then see if it is solved. While you are at it you could add heatsinks to the fresh Tr5 and Tr6.
Please think what those caps do when the amp is powered on....They can not cause the issues the amplifier has. They could cause other issues if they would be defective. I learnt it is better to solve real problems first instead of creating other problems to solve...but that could entirely be my dutch upbringing
I would replace Tr1 to Tr6 and the 18V Zener diode without blinking an eye and then see if it is solved. While you are at it you could add heatsinks to the fresh Tr5 and Tr6.
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Limited is the right word!
They can not cause the issues the amplifier has. They could cause other issues if they would be defective. I learnt it is better to solve real problems first instead of creating other problems to solve...but that could entirely be my dutch upbringing
I would replace Tr1 to Tr6 and the 18V Zener diode without blinking an eye and then see if it is solved. While you are at it you could add heatsinks to the fresh Tr5 and Tr6.
Thanks again,. Jean-Paul.
I'm going to order some more parts today. Was wondering about the 18v Zener diode, are there .ore than one of these? I've looked at all the diodes on the schematic but it's not clear (to me).
Thanks
Can anyone suggest a suitable substitute for the 2SC1628-Y (x2) ?
Replacement and equivalent transistor for the 2SC1628-Y
EL-componant suggests:
"You can replace the 2SC1628-Y with the 2SC2231, 2SC2231A or 2SC2483".
Having a hard time finding 2SC1628-Y, there is a seller on eBay but they're after £25 for a pair which seems a bit high...
Replacement and equivalent transistor for the 2SC1628-Y
EL-componant suggests:
"You can replace the 2SC1628-Y with the 2SC2231, 2SC2231A or 2SC2483".
Having a hard time finding 2SC1628-Y, there is a seller on eBay but they're after £25 for a pair which seems a bit high...
All done, no pops or crackles. So far so good!
I have noticed that the characteristics have changed, in particular bass reproduction seems to have been effected by the new transistors. Bass in much quieter on the settings I used to use, if I turn the bass potentiometer around to 3 quarters full volume I get a better mix of bass/treble but its not quite as it should be. As an example, I'm listening to the Police - So lonely, a song with very prominent bass.
The lower bass notes are much louder than the higher ones which sort of disappear into the mix the higher up the scale he plays.
Not sure what transistors would affect this but maybe I could try another type?
I did exactly this:
2SA841-BL --> 2N5401
2SC1628-Y --> 2N5551
2SC1624-y --> BD139
2SA814-Y --> BD140
It doesn't sound bad at all, in fact it sounds pretty great for the most part. Just this weird lack of bass on certain parts of the frequency spectrum.
I have noticed that the characteristics have changed, in particular bass reproduction seems to have been effected by the new transistors. Bass in much quieter on the settings I used to use, if I turn the bass potentiometer around to 3 quarters full volume I get a better mix of bass/treble but its not quite as it should be. As an example, I'm listening to the Police - So lonely, a song with very prominent bass.
The lower bass notes are much louder than the higher ones which sort of disappear into the mix the higher up the scale he plays.
Not sure what transistors would affect this but maybe I could try another type?
I did exactly this:
2SA841-BL --> 2N5401
2SC1628-Y --> 2N5551
2SC1624-y --> BD139
2SA814-Y --> BD140
It doesn't sound bad at all, in fact it sounds pretty great for the most part. Just this weird lack of bass on certain parts of the frequency spectrum.
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Pleased to hear you fixed it in the end
Different semiconductors will not affect the bass response at all. If you have doubts on the response then two key things to do are to play a 20Hz (or lower) to 20kHz test track and look with a scope at the output. Set the timebase really slow to cater for the 20Hz signal and then just look at the amplitude and make sure it is constant as F rises.
Another good check is by using a squarewave for both bass and treble and checking that it is passed correctly. A digital squarewave (test CD for example) is fine for the bass but no good for high frequencies.
To change the actual 'turnover' frequencies of the tone controls, in other words where in the frequency range they have effect would mean altering component values, and if the controls are wrapped around the power amp feedback loop (some old Japanese amps did favour that approach) then altering it could lead to stability issues.
Different semiconductors will not affect the bass response at all. If you have doubts on the response then two key things to do are to play a 20Hz (or lower) to 20kHz test track and look with a scope at the output. Set the timebase really slow to cater for the 20Hz signal and then just look at the amplitude and make sure it is constant as F rises.
Another good check is by using a squarewave for both bass and treble and checking that it is passed correctly. A digital squarewave (test CD for example) is fine for the bass but no good for high frequencies.
To change the actual 'turnover' frequencies of the tone controls, in other words where in the frequency range they have effect would mean altering component values, and if the controls are wrapped around the power amp feedback loop (some old Japanese amps did favour that approach) then altering it could lead to stability issues.
Maybe not all the transistors needed to replace, you can try put back the driver transistors 2SA814 and 2SC1624(do it one channel one time) and test it again.
I went with .5w 15v Zener diode.
I will try replacing as suggested and listen for difference. I'm pretty sure the traces won't lift, the solder flows real quick and I have a suction solder remover so can get it done without excess heat.
Jean-Paul, you say give the parts some time, I didn't think there was a break in period with transistors? Or did you mean give it time to see if I get on with it better?
It's really seriously lacking in bass so I think I'm going to have to try other things.
I will try replacing as suggested and listen for difference. I'm pretty sure the traces won't lift, the solder flows real quick and I have a suction solder remover so can get it done without excess heat.
Jean-Paul, you say give the parts some time, I didn't think there was a break in period with transistors? Or did you mean give it time to see if I get on with it better?
It's really seriously lacking in bass so I think I'm going to have to try other things.
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