I don't knwo yet what to think, but I loved to eared the sound before. Even as you know their is electronics elements of facts and ears at the end and all the chain of components including the record studio itself too...
May I conclude that for the transistor replacements after Motorola having passes the hands to OnSemi :
A8 -> 2N5878 ->MJ150025 ( PNP )
A6 -> 2N5876 -> MJ150024 ( NPN )
Correct ?
May I conclude that for the transistor replacements after Motorola having passes the hands to OnSemi :
A8 -> 2N5878 ->MJ150025 ( PNP )
A6 -> 2N5876 -> MJ150024 ( NPN )
Correct ?
Hi,
It seams that I am accumulating bad luck...
The track silver colored on the PCB negative chanel "pc OS 1 b" has been snatched when I was unsoldering on of the cables solded. My hand push the "green" cabled and it snatches the track from the PCB...
Most likely due to his old age...
Olivier
It seams that I am accumulating bad luck...
The track silver colored on the PCB negative chanel "pc OS 1 b" has been snatched when I was unsoldering on of the cables solded. My hand push the "green" cabled and it snatches the track from the PCB...
Most likely due to his old age...
Olivier
in fact it was not the cupper but the thin layer covering the cupper track in tin that was snatched. so the repair is simply to sold back after cleaning the cupper track no more the cleaning will be important to prevent any self or capacitor effect.
I just ordered the NPN and PNP transistors for ending my repair from OnSemi distributor. They should arrive in a couple of days.
I am anticipating that perhaps I should change the resistance too if the fonctioning point of the transistor on its line is not good...
I just ordered the NPN and PNP transistors for ending my repair from OnSemi distributor. They should arrive in a couple of days.
I am anticipating that perhaps I should change the resistance too if the fonctioning point of the transistor on its line is not good...
Hi Oliver, just curious are you using mica insulators/heat sink compound on the TO-3's? I've got some work to do on a S/350e and was looking into changing over to Sil pads. I used to repair a lot of amps many years ago and haven't done it in a while, so I was looking to see what if any improved options are now available.
Thanks,
Kevin
If you don't like goo, look for Keratherm® Red.
Personally, I like the ceramic ones, still need goo though.
I don’t mind the gout. When I install my transistors I make sure that I don’t see goo oozing out and I like a nice clean look when it’s finished. What I was looking for was something with out the goo that would also have better thermal performance without having any reliability issues long-term.
Thanks
Kevin
I am the original owner and need help with my 400A. The right channel is working fine.
It has a DC offset of 15mv. The left channel has a DC offset of 120mv. but no output.
The fuse is not burnt and it has the + and - 60 volts at the rails but, it does not warm up at idle. It seems like the output transistors are not being driven but I can't spot and burned parts or bad solder joints. Any suggestions where I should start looking?
It has a DC offset of 15mv. The left channel has a DC offset of 120mv. but no output.
The fuse is not burnt and it has the + and - 60 volts at the rails but, it does not warm up at idle. It seems like the output transistors are not being driven but I can't spot and burned parts or bad solder joints. Any suggestions where I should start looking?
*************************************************************
The next day I moved the 5K trimmer resistor and the left channel started warming up and I set it to draw .4 amps at a temperature of 40 degrees C.
The issue that I'm having now is that the DC offset is -70mV. Should I replace the 10 mfd and the 470 mfd electrolytic capacitors?
Hello, Mr. Pass,
Thank-you for your response. I replaced the 5K Cermet Trim Pot and bias to 50 deg C. The offset fluctuates between 100mV to 80mV. The issue that I'm having is that the speaker pops on turn-on and turn-off. The other channel is fine and the offset is 20mV.
P.S. I also own a CAS-1 and over 30 years ago I built a 40A from your schematics.
Thank-you for your response. I replaced the 5K Cermet Trim Pot and bias to 50 deg C. The offset fluctuates between 100mV to 80mV. The issue that I'm having is that the speaker pops on turn-on and turn-off. The other channel is fine and the offset is 20mV.
P.S. I also own a CAS-1 and over 30 years ago I built a 40A from your schematics.
I replaced all the electrolytic capacitors including the two 9800 mfd. in the power supply. I replaced them with 22,000 mfd. Being concerned about the inrush current on turn-on, I also installed a thermistor CL-60. I don't see any negative results from having done this. The offset is 20mV on both channels. After playing music for a couple of hours, the temperature is at 52°C. The 400A sounds great again!
I think I might have a couple. I would have to go to storage to check.
