meeskees

Thanks for your detailed response, James. So far I have only resoldered the tube sockets and filament connections. I will re-solder the other soldered connections in a few weeks. Unfortunately I don't own an oscilloscope and I wouldn't know how to use such a device. I'm not that technical. For now I'll leave it at that, because the amplifier will eventually function normally after three minutes and my health won't leave much room for any effort in the coming weeks.

Par already pointed it out to me and now Kevin Gilmore has done so too, so who am I to doubt these authorities. This afternoon I removed the board again and re-soldered the connector for the filaments. To be on the safe side, I also provided the tube socket pins with fresh solder. Once everything was put back together, I turned on the amp. And.......no hum this time. Unfortunately we cheered too early. After dinner I wanted to listen to music and the hum was present again, but fortunately it disappeared again after 3 minutes. A short circuit doesn't seem likely to me, because when I swapped the board, the hum moved with the board, while I had connected the other winding for the filament voltage

My amplifier also contains an Alps R27. The position of this potentiometer has no influence on the hum. The current state of affairs is that, after switching on, I have 3 minutes of hum in the right channel (after exchanging the boards and then the amplifier is silent and everything functions as it should. The tubes are not the cause of the hum, because the phenomenon also occurs with other pairs of tubes. Both with GE and RCA tubes. So apparently there is an imbalance that is resolved after three minutes. Fortunately I can just listen to music, but if anyone has a good tip?

In Europe, at least in the Netherlands, lead-containing solder is still widely available. When I cleaned my boards of flux residue, I checked all solder joints with a loupe for cold welds or bad connections. I couldn't find any errors and thought I had actually soldered it very neatly Coincidentally I discovered today that the hum disappeared after just over three minutes. Until now I switched off the amplifier as soon as a hum was heard.To be on the safe side, I replaced the tubes of the right channel with another pair, but that makes no difference. The hum also lasts about 3 minutes before it disappears.I am going nuts of those tubes.

Last night I wanted to listen to music. Unfortunately the hum was back, but this time, as expected, in the right channel. After adjusting the offset and balance, everything worked properly again. I have no idea why I have to readjust everything after every listening session. All suggestions are welcome

This morning the hum was prominent immediately after switching on. Today I had some free time and I swapped the amp boards to see, as mwl168 suggested, if the hum moved with the board. I have no idea yet, because after switching the amplifier on and off 3 times, no hum has been heard and I am now listening to music. I don't know yet whether this has solved the problem. In any case, thanks for the suggestions made

Today I removed the left amplifier board from the housing. There was nothing wrong with the Phoenix connectors. They were still perfectly connected to the PCB and the connection to the cables was as it should be. I cleaned the bottom of the print with alcohol to remove any flux residue. After adjusting the offset and balance, I turned off the amplifier and activated the servo. After switching on I heard the familiar hum again, only softer this time. After a few minutes the hum disappeared and I can enjoy the music as usual. I don't feel like I've really solved the problem yet. So if anyone has any suggestions, please let me know

They are indeed Phoenix connectors. I'll start working on it tomorrow. Thank you for this practical tip. The problem cannot be very serious, because the amplifier also works well from time to time.

After almost ten years of loyal service, my KGST is starting to show signs of malfunction. Since last week I have a loud hum in the left amplifier channel. I replaced the tubes with another pair and readjusted the balance and offset. No hum could be heard and I could enjoy the music undisturbed again. The next day the hum unfortunately returned. Readjust everything and the hum was gone. After switching the amplifier off and on again, the hum returned. I have swapped the filaments, but that didn't solve the problem. I also left the gyro turned off, but that doesn't make any difference either. Hopefully someone has a good tip to try.

After almost ten years of loyal service, my KGST is starting to show signs of malfunction. Since last week I have a loud hum in the left amplifier channel. I replaced the tubes with another pair and readjusted the balance and offset. No hum could be heard and I could enjoy the music undisturbed again. The next day the hum unfortunately returned. Reset everything and the hum was gone. After switching the amplifier off and on again, the hum returned. I swapped the filaments, but that made no difference. I also left the servo turned off, but that didn't make any difference. Hopefully someone has a good tip to try.

That's what I remember too,but I had the feeling the RCA's are more involving and the bass was a bit tighter.

That would be interesting. I have compared GE and RCA ones. It wasn't easy because it takes quite some time to change the tubes and set the offset and balance again. I thought the RCA's were the better ones, but I am not really sure about that.Good luck!

It is the Korean version.You have to look at the self price quote. Look also at the kakaku site for prices.

http://www.pricejapan.com/k_front/k_good_info.php?code=536&category=10

Not a Mk3.0?