Over the last week I rebuilt my recently acquired SA-9800. The reason for the rebuild was to ensure reliability.
The following were the power supply voltages before the rebuild. Values in bold are from my amplifier
AWR-194 (Power Supply Assy)
pins 1&2: -51.9v regulated, -52v
pins 3&4: +52.5v regulated, +52v
pins 5&6: +32.4v regulated, +32v
pin 7: +19.2v regulated, +18v
pin 8: 0v, ground
pin 9: -53.1 -50v, raw, unregulated
pins 10&11: -32.6/ 32.6 v regulated, -32v
pin 12: 50.7 +49v unregulated raw
pin 13: 70.4 +69v unregulated raw
pin 14: 0v, ground
pin 15: -71.5 -70v unregulated raw
pin 16: 54.3 +6.7vac, this is an AC voltage - this voltage was taken while the pilot light was burnt.
pin 17: 54.4 +53.4vac, this is an AC voltage
pin 18: 54.6 +53.7vac, this is an AC voltage
This is the pic before the repair -
As you can see it is in pretty good nick
This is a pick after the rebuild.
Please note that I have soldered the D4 diode in the wrong direction, I corrected this after the picture was taken
What I have done is -
Change upgrade all transistors apart from Q5 and Q6 as per Solutionrooms list.
Change all diodes
Change all resistors to high precision military grade metal films of the same power rating except the R20 because I could not find a similar heat handling metal film.
The board has been upgraded to the AWR-196 European/HG version with 4 transistors to handle the heat with new heat sinks. The new heat sinks are 26mm tall and touches the metal undercover when closed. So these heat sinks have been isolated from the collector of the transistor with silicone pads sandwiched between thermal paste.
I left the ceramic caps alone.
I did not change the chassis mount R1 and R2 between pins 15&9 and pins 12&13
These are the voltages after the rebuild.
pins 1&2: -50.9v regulated, -52v
pins 3&4: +50.9v regulated, +52v
pins 5&6: +31.5v regulated, +32v
pin 7: +18.5v regulated, +18v
pin 8: 0v, ground
pin 9: -55.1 -50v, raw, unregulated
pins 10&11: -31.3 v regulated, -32v
pin 12: 51.9 +49v unregulated raw
pin 13: 72.3v +69v unregulated raw
pin 14: 0v, ground
pin 15: -71.5 -70v unregulated raw
pin 16: 55.3 +6.7vac, this is an AC voltage - this was before the pilot lamp was replaced.
pin 17: 55.3 +53.4vac, this is an AC voltage
pin 18: 55.3 +53.7vac, this is an AC voltage
My findings
The Q11,12,13 and 14 still run finger burning hot. I'm not sure whether I converted 2 burning transistors to 4 burning transistors.
My questions
1) Will replacing the chassis mount R1 & R2 will help to bring the pin 9 and 12 voltages more towards the spec?
2) I have a few 2SK30A-Y transistors, will replacing the Q5 & Q6 with these will be a good idea?
The following were the power supply voltages before the rebuild. Values in bold are from my amplifier
AWR-194 (Power Supply Assy)
pins 1&2: -51.9v regulated, -52v
pins 3&4: +52.5v regulated, +52v
pins 5&6: +32.4v regulated, +32v
pin 7: +19.2v regulated, +18v
pin 8: 0v, ground
pin 9: -53.1 -50v, raw, unregulated
pins 10&11: -32.6/ 32.6 v regulated, -32v
pin 12: 50.7 +49v unregulated raw
pin 13: 70.4 +69v unregulated raw
pin 14: 0v, ground
pin 15: -71.5 -70v unregulated raw
pin 16: 54.3 +6.7vac, this is an AC voltage - this voltage was taken while the pilot light was burnt.
pin 17: 54.4 +53.4vac, this is an AC voltage
pin 18: 54.6 +53.7vac, this is an AC voltage
This is the pic before the repair -
As you can see it is in pretty good nick
This is a pick after the rebuild.
Please note that I have soldered the D4 diode in the wrong direction, I corrected this after the picture was taken
What I have done is -
Change upgrade all transistors apart from Q5 and Q6 as per Solutionrooms list.
Change all diodes
Change all resistors to high precision military grade metal films of the same power rating except the R20 because I could not find a similar heat handling metal film.
The board has been upgraded to the AWR-196 European/HG version with 4 transistors to handle the heat with new heat sinks. The new heat sinks are 26mm tall and touches the metal undercover when closed. So these heat sinks have been isolated from the collector of the transistor with silicone pads sandwiched between thermal paste.
I left the ceramic caps alone.
I did not change the chassis mount R1 and R2 between pins 15&9 and pins 12&13
These are the voltages after the rebuild.
pins 1&2: -50.9v regulated, -52v
pins 3&4: +50.9v regulated, +52v
pins 5&6: +31.5v regulated, +32v
pin 7: +18.5v regulated, +18v
pin 8: 0v, ground
pin 9: -55.1 -50v, raw, unregulated
pins 10&11: -31.3 v regulated, -32v
pin 12: 51.9 +49v unregulated raw
pin 13: 72.3v +69v unregulated raw
pin 14: 0v, ground
pin 15: -71.5 -70v unregulated raw
pin 16: 55.3 +6.7vac, this is an AC voltage - this was before the pilot lamp was replaced.
pin 17: 55.3 +53.4vac, this is an AC voltage
pin 18: 55.3 +53.7vac, this is an AC voltage
My findings
The Q11,12,13 and 14 still run finger burning hot. I'm not sure whether I converted 2 burning transistors to 4 burning transistors.
My questions
1) Will replacing the chassis mount R1 & R2 will help to bring the pin 9 and 12 voltages more towards the spec?
2) I have a few 2SK30A-Y transistors, will replacing the Q5 & Q6 with these will be a good idea?
Last edited: