Technics SA-424 Restoration

[Ldsc2002]

Hi,

I just bought this Technics SA-424 receiver, and I am looking at restoring it. The amp is in pretty good condition, but there are some things that need fixing.



The first one is the volume potentiometer, which is really dirty and makes a lot of noise when changing the volume. Is deoxit the best option for fixing this or should I try to take it apart to clean it?

The second thing I have to fix is the light bulb for the analog tuner meter. What would be a suitable replacement for this bulb? The service manual says it is a 6.3V 0.25A bulb but the original part number is no longer available.

Lastly, one of the speaker terminals appears to be stuck, is there anything I can do to fix it or is my only option replacing the speaker connection board?

Any help will be greatly appreciated!

 

[Ldsc2002]

After a good cleaning, polishing the glass, and changing the tuner bulb, this thing looks almost brand new! I haven't had time to listen to it a lot, but I like what I hear so far.



Measuring DC offset, it hovers around 6mv on both channels. I think someone replaced the STKs at some point, as they look much newer than the rest of the amplifier. Should I try measuring ICQ voltage? I understand it's an old amp and it might need adjusting, but I don't want to risk shorting something if its not worth it.

For what it's worth, I measured the temperature on both STKs after an hour or two of running with a pair of B&W 606 speakers, and they both were around 95 degrees. I also noticed R711 is running really hot, around 160 degrees and enough to scorch the board, is this normal?

 

[Jim Russo]

Hi, Just ran across this thread. I'm the original owner of a SA-424 and it always had an overheating problem, even when new, which I worked around by running a small fan behind the unit. Fast forward 40 years and it's on the shelf after a stint in the garage. I thought I would go through it and Deoxy/Fader Lube the volume pot and some sticking switches. After doing that and testing it on the bench I noticed the smell of cooking electronics even when it was plugged in, even if turned off- I thought maybe the result of a dusty garage environment, but it didn't resolve with a thorough cleaning. The source seems to be the resistor you pointed out which runs hot and I was thinking of replacing it with one rated at a higher wattage. I wonder what you did to hopefully solve the issue.

 

[MCS3125]

Just in case anyone wants to know what dial lamp is in the SA-424 (and SA-222), it is a 6.3v wedge type lamp 0.25A. Mine said Stanley 259, so I assume a standard automotive 259 lamp. The silicone grommet that the lamp fits into said "Stanley" as well and the lamp terminals were crimped onto the wires, so it must've been some type of lamp assembly.

 

[MCS3125]

Just in case anyone wants to know what dial lamp is in the SA-424 (and SA-222), it is a 6.3v wedge type lamp 0.25A. Mine said Stanley 259, so I assume a standard automotive 259 lamp. The silicone grommet that the lamp fits into said "Stanley" as well and the lamp terminals were crimped onto the wires, so it must've been some type of lamp assembly.

The 259 bulb did the trick. Soldered on to the existing harness. Photo of the original bulb below.