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Vintage Sony TA-8650 V-FET Integrated Amplifier

Jon S

Jon S

Super Member
I have a vintage near mint 1974 Sony TA-8650 V-FET amplifier which EchoWars serviced several years ago, replacing bad parts, diodes and restoring it to spec. I rarely used the amp, maybe putting a hundred hours since the repair. I have now put the amp into service and it sounds really smooth with great imaging and soundstage, beating any amp that I have or had since.

Now my question is, how often should i have it serviced? It sounds okay now and the top panel gets extremely hot (characteristic of a V-FET amplifier). I would ask EchoWars but it seems he has not posted in over a year (I hope he's okay.) I know that some of the knobs and switches needs cleaning because there is static when turning or buttons are sticky when pushed.

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I have a restored TAN-8550 V-FET power amp, and it doesn’t get unusually hot in use. Sony issued a service bulletin for all the V-FET amps in this series, specifying a lower bias setting. Yours may need to be adjusted. It also may need some caps replaced, if they’re all the originals - those weren’t designed to last over 40 years.
 
Sony V-FET amps all get hot... I have owned a few of them (all brand new) and they all did get very hot.

If you look at Nelson Pass's custom V-FET amp that he demoed in 2014, you will see the case was a humongous heat sink. That amp generated 100 watts. Pass made eight amps, gave six to Sony and kept two for himself.

For some reason, my original post did not show the images... The pics here are of the Pass V-FET amp and my Sony TA-8650. Early production models of the Sony did not have the metal chimneys around the power transistor boards. The odd thing about the Sony is that it only had one capacitor for the power supply, I never saw that before.
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If the amp was running at that temp when it came back to you from Echowars then its probably running at the right temperature. Although you may still need other owners with this amp to confirm that.

I have 2 VFET amps - they are homebrew and both of these do run pretty warm - but even the one running in Class A doesnt get "extremely" hot.

This would be something I would confirm if I were you.
 
hi everyone, looking for 4 sony VFET for my sony TA 4650 vfet integrated amp, does anyone have spare VFET that I can buy, thanks! Ali
 
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