Sony TA-8650 restoration

[mattworld]

Hi,

I am working on a new project, the restauration of a Sony TA 8650. It was sold as making noise but not working. I hope it is not the VFET.

I am not familiar with this model. Can you advice me ?
What components should I replace before switching it on ? What voltage should I check for the VFET ?

 

[Old'n'Cranky]

Stop.

Have a read of the other threads regarding sony v-fet amps and their repairs / restoration.

If after reading those you really think you have the equipment and skills, then go for it.

Otherwise you will need to find an experienced tech to do the work for you.

 

[kannan_s]

Please read threads on restoring Sony VFET amps like TA 5650 / TA 4650 as well as mention about this amp in Audiokarma website - if you google restoring or repair of SONY VFET amps, you will see dozen or more hits. They were all well documented. Your amp is well regarded second generation one but you have to exercise caution in restoring. You should not use Variac for powering these as slow rise of Input power will destroy the VFET. I had recently restored TA 5650 which came to me with broken non working Power supply.
Read a lot before embarking on restoring and it is worthwhile effort. You will definitely find the unique sound quality VFET amplifiers enjoyable.

 

[mattworld]

Hi,

Ok, thanks for your response. I already start reading threads about this amp.
I will start by removing and verify all the VFET impedances.

Here is what I plan to do :
- I need to change the 7 VD-1221M diode with dual 1N4148.
- Replace all the electrolytic and film caps on the power, pre and power bords.
- Verify the preamplifier functionality
- I'will next verify voltages on the power bord without the power transistor and place then on the radiator with new thermal paste.
- Verify the voltage drop on R737 and R787 without the +/- 60V
- Make the bias ajustement and the DC balance.

I still have questions : what's is the bias voltage for the amp. Do I need to change all the films caps (this amp is from 1975).

 

[Old'n'Cranky]

If you keep reading all the v-fet articles (both here and in Pass forum) I suspect you will find everything you need.

Plenty of others have asked about film cap replacements so just keep on reading.

Sorry if this seems like a short (cranky) answer, but there are sooo many posts from beginners about caps, and caps, and more caps, and not one of them does their own research.
Sooo many posts. Maybe try using the forum search function for 'replacing film caps' ?

 

[rottalpha]

.. Your amp is well regarded second generation one

The TA-8650 is a first gen v-fet (integrated) amp...IIRC, it is the first V-fet amp to hit the market anywhere...