So by drivers you mean that I need to replace TR9 and TR11?
TR11 unfortunatelly was replaced with a BC327 which I was told that it's a substitute for 2SA697 because the original was faulty.
As far as all the other transistors are concerned they are all original.
The bias setting was to minimum (0) during all the measurements - I don't know if it's wrong or right. I thought it doesn't need to be adjusted since it doesn't affect the channel.
"give minimum bias and that is when the pre-set is on maximum resistance". I don't really understand what you mean by that Mooly.
So before anything else do I need to replace these transistors? Any common substitutes ? The originals are long gone.
Bulb tester is in place.
TR11 unfortunatelly was replaced with a BC327 which I was told that it's a substitute for 2SA697 because the original was faulty.
As far as all the other transistors are concerned they are all original.
The bias setting was to minimum (0) during all the measurements - I don't know if it's wrong or right. I thought it doesn't need to be adjusted since it doesn't affect the channel.
"give minimum bias and that is when the pre-set is on maximum resistance". I don't really understand what you mean by that Mooly.
So before anything else do I need to replace these transistors? Any common substitutes ? The originals are long gone.
Bulb tester is in place.
TR07 is configured as a rubber diode (lol I'd never heard that one either until quite recently). Its a vbe multiplier 
Rubber diode - Wikipedia
You get minimum bias when that transistor is fully on. That means it appears as virtually a short between collector and emitter and that happens then the pre-set is is turned to appear as 470 ohms and not zero ohms.
So between B and E you want it to be 1470 ohms in total and not 1k.
Certainly TR11 needs replacing and I would replace TR9 as well.
Two common types often used for drivers are MJE340 and MJE350 and BD139 and BD140.
The BC327 is underrated here as I think was pointed out earlier. It could see higher than its voltage rating under signal conditions. Another possible is the 2N5401 and 2N5551 but they are becoming obsolete. The BD and MJE devices are more rugged.
Rubber diode - Wikipedia
You get minimum bias when that transistor is fully on. That means it appears as virtually a short between collector and emitter and that happens then the pre-set is is turned to appear as 470 ohms and not zero ohms.
So between B and E you want it to be 1470 ohms in total and not 1k.
Certainly TR11 needs replacing and I would replace TR9 as well.
Two common types often used for drivers are MJE340 and MJE350 and BD139 and BD140.
The BC327 is underrated here as I think was pointed out earlier. It could see higher than its voltage rating under signal conditions. Another possible is the 2N5401 and 2N5551 but they are becoming obsolete. The BD and MJE devices are more rugged.
TR07 is configured as a rubber diode (lol I'd never heard that one either until quite recently). Its a vbe multiplier
Rubber diode - Wikipedia
You get minimum bias when that transistor is fully on. That means it appears as virtually a short between collector and emitter and that happens then the pre-set is is turned to appear as 470 ohms and not zero ohms.
So between B and E you want it to be 1470 ohms in total and not 1k.
Certainly TR11 needs replacing and I would replace TR9 as well.
Two common types often used for drivers are MJE340 and MJE350 and BD139 and BD140.
The BC327 is underrated here as I think was pointed out earlier. It could see higher than its voltage rating under signal conditions. Another possible is the 2N5401 and 2N5551 but they are becoming obsolete. The BD and MJE devices are more rugged.
Thanks a lot for the advice ad suggestions Mooly.
Before I go to buy those transistors should I set the TR07's B and E resistance to 1470ohms? If yes how can I do it since the bias pot doesn't react so far?
I also think I should also buy a couple of output ones (TIP 41-42) like the other channel, just in case they are burnt or something. What do you think?
Yes, make sure the amp is OFF and just turn the preset now to its maximum resistance.
Remember that in circuit the resistance readings may appear wrong but it should be easy to see which way way to turn it.
Put your meter on ohms and connect it between B and E of TR07. Turn the pot fully one way and look at the resistance reading and then turn fully the other way and look at the resistance.
Select the direction that gave the highest total resistance. Be sure to use a ohms range and not the diode range on your meter.
Make sure you get the C versions of the TIP transistors if possible. These are 100v rated. The 80 volt B version are also OK for your amp as a second choice.
Remember that in circuit the resistance readings may appear wrong but it should be easy to see which way way to turn it.
Put your meter on ohms and connect it between B and E of TR07. Turn the pot fully one way and look at the resistance reading and then turn fully the other way and look at the resistance.
Select the direction that gave the highest total resistance. Be sure to use a ohms range and not the diode range on your meter.
Make sure you get the C versions of the TIP transistors if possible. These are 100v rated. The 80 volt B version are also OK for your amp as a second choice.
So it was set to maximum resistance
If you prefer
. You can say full left or CCW. Ok...resistance helps a lot.Success. Replaced all 4 transistors and now both channels bias and work as they should.
Before I rehouse the whole thing I need to express my sincere gratitude to the forum moderator Mooly. Without his experience, guidance and advice it wouldn't have happened.
Thanks everybody for the input, interest and help.
DIYAUDIO rules.
Before I rehouse the whole thing I need to express my sincere gratitude to the forum moderator Mooly. Without his experience, guidance and advice it wouldn't have happened.
Thanks everybody for the input, interest and help.
DIYAUDIO rules.
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