i will try to measure it in the evening again...
have to reconnect it.
It is cheap, not good. Whoever invented it, it is simply not how TO3 should be mounted.
First thing I did when I repaired A1's was to make this better. With 2 lugs per transistor. Also the replacement transistors casing material not always allowed for soldering to the casing and I at least had it once that there was a dry joint and a loose wire.
If it is an early one I recall also mains wiring to be eh.... particular.
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i checked and there is no connection from collector to the aluminium. so insulation is ok.
collector has good contact to wire.
collector has good contact to wire.
what do you mean with mains wiring?
i had to replace the transformer because it was defective.
By the way, it's not the full 20W in class A, only the first 8 W I believe. Although it gets hot enough to boil an egg on it.
For anyone that wants to play:
with 0.22 ohm resistors it runs at 260ma bias current and around 6.5 watt dissipation per output transistor.
Begin by measuring voltages carefully. You need to measure both to the transistors and also across the base/emitter junctions. Each junction should be around 0.6 to 0.7 volts if turned on.
This path should be trying to turn on the upper output (same for the lower). You have to see why that is not happening.
I'll look in later 🙂
For anyone wanting to try the sim you will have to put your own model in place.
with 0.22 ohm resistors it runs at 260ma bias current and around 6.5 watt dissipation per output transistor.
Begin by measuring voltages carefully. You need to measure both to the transistors and also across the base/emitter junctions. Each junction should be around 0.6 to 0.7 volts if turned on.
This path should be trying to turn on the upper output (same for the lower). You have to see why that is not happening.
I'll look in later 🙂
For anyone wanting to try the sim you will have to put your own model in place.
Are TR1 TR2 TR3 TR4 surely good? If yes, maybe R6 & R11 value needs tweaking in order to turn on the replaced output transistors?
yes I replaced them with BC550C and BC560C.
i measured them now and they are fine...
I will have a look in the evening if i can measure and update here...
i measured them now and they are fine...
I will have a look in the evening if i can measure and update here...
i replaced the R30 and R31 with 0R47 instead of 0R22, because they were installed before also with value 0R47.
I just replaced them with 3W.
Why use the most noisy transistors one can find?
You had a defective transformer. Mmmm. Burnt/open primary? Probably already asked but are the rectifiers still OK and what about the voltages? All good?
With this master piece of unreliability I had more than once detective rectifiers and filter caps. Also input selector and volume potentiometer.
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It was already confirmed that supply valtages are fine.
...
BC550, 560 may not be the first choice in phono stages,
but here it does not matter.
...
BC550, 560 may not be the first choice in phono stages,
but here it does not matter.
This is an intersting remark. However the output devices should turn "on" by themselves via the
path in red of post 26, only if a certain level is exceeded bias will be balanced by the input pairs.
What were the defects exactly!? You have to be more precise in answers. We can not possibly know what was detective and what you have done unless you tell us. The exact fault of parts may indicate why and what went wrong and why you can’t solve your problem.
Some will know what I mean. Nothing happened, the device just stopped, repair should not cost too much and then the repair guy discovers the device had 400V.
So transformer, all transistors, filter caps and rectifiers were replaced?
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okay.
here we go.
replaced:
transformer
rectifier diodes
output transistors
driver transistors
electrolytics
all 1W to 5W resistors.
some blown resistors and transistors in the phono power supply.
i think this is it
here we go.
replaced:
transformer
rectifier diodes
output transistors
driver transistors
electrolytics
all 1W to 5W resistors.
some blown resistors and transistors in the phono power supply.
i think this is it
1. What were the defects of the parts?
2. Did you simply replace anything except the PCB as it was total loss?
3. Are you very sure you replaced the NPN and PNP transistors for NPN and PNP transistors?
4. Did you buy original transistors by normal brands or Aliexpress versions?
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