MattiaM
Active Member
I got my hands on a beautiful TA-8650 that I bought broken a couple of weeks ago and brought back to life.
It's the best example I have ever come across, nobody had ever worked on it, and it was in storage for a very long time (in a very dusty place). It came with 3 of 2SK60 gone and a burnt resistor, but I had 3 spare ones laying round with the same ranking, so after cleaning it (a LOT of dust) and recappping it entirely, it was up and again ready to be tested. All the biases checked correctly, the DC offeset too, I plugged the oscillocope and the signal generator and... nothing. No waveforms at all.
After a bit of troubleshooting, it turned out it was the switches, that were still in need of more cleaning (at firist I thought one of the ICs had gone bad). After taking them all apart (what a pain), now the amplifier is back and works quite nicely.
Two things though do not seem quite right:
the first is that it runs HOT. I am used to the fact that vfet amplifiers run hot, I have already a TA-4650, two 5650, and also a TA-F7 in my collection, but this one is on another level hot: I can't really keep my hand on the top cover at all, because it just burns, although the thermistors never sent the amplifier into overheat protection for now, even after a few hours of continuous operation. Is it normal that it is that much hotter of a 5650?
The second problem is a slighlty annoying hiss from the speakers, regardless of the volume, which can be heard quite distinctly at equal levels in both channels. I assume it is a power supply issue, although I have not investigated much for now.
In case I decided to replace the main filtering caps, those in the TA-8650 are quite unique. It has two double filtering caps, one large one with two 10000uF caps inside, and a smaller one with two 3000uF caps.
As the amplifier looks pristine, I want to keep the cans of the original caps to keep the original look. Especailly for tube gear, I have seen people emptying the cans and using them to put modern replacement caps inside, but I have never done it myself. Has anyone got any suggestions on how to do that?
It's the best example I have ever come across, nobody had ever worked on it, and it was in storage for a very long time (in a very dusty place). It came with 3 of 2SK60 gone and a burnt resistor, but I had 3 spare ones laying round with the same ranking, so after cleaning it (a LOT of dust) and recappping it entirely, it was up and again ready to be tested. All the biases checked correctly, the DC offeset too, I plugged the oscillocope and the signal generator and... nothing. No waveforms at all.
After a bit of troubleshooting, it turned out it was the switches, that were still in need of more cleaning (at firist I thought one of the ICs had gone bad). After taking them all apart (what a pain), now the amplifier is back and works quite nicely.
Two things though do not seem quite right:
the first is that it runs HOT. I am used to the fact that vfet amplifiers run hot, I have already a TA-4650, two 5650, and also a TA-F7 in my collection, but this one is on another level hot: I can't really keep my hand on the top cover at all, because it just burns, although the thermistors never sent the amplifier into overheat protection for now, even after a few hours of continuous operation. Is it normal that it is that much hotter of a 5650?
The second problem is a slighlty annoying hiss from the speakers, regardless of the volume, which can be heard quite distinctly at equal levels in both channels. I assume it is a power supply issue, although I have not investigated much for now.
In case I decided to replace the main filtering caps, those in the TA-8650 are quite unique. It has two double filtering caps, one large one with two 10000uF caps inside, and a smaller one with two 3000uF caps.
As the amplifier looks pristine, I want to keep the cans of the original caps to keep the original look. Especailly for tube gear, I have seen people emptying the cans and using them to put modern replacement caps inside, but I have never done it myself. Has anyone got any suggestions on how to do that?