'Sounds heat related to me and as the first reply pointed out, the amplifier is 38 years old. Now what happens to electrolytic capacitors over such a long time, I wonder?
Yep, they dry out and fail - heat exacerbates the problems. Do everyone, including the amplifier, a favour and replace the capacitors - all of the electrolytics with suitable modern versions of the old ones which will not only be unaobtanium but also useless by now. Even if the problem is not actually down to a cap, you still need to do this if it has not already been done in the last 20 years.
The usual culprits on these amps (notwithstanding age of caps etc...), are the switches (corrosion) and relays (corrosion and micro-arcing due to offset drift with time).
Aside from that they do have a few known problems such as thermal transfer grease drying up, and potentially deadly problems with bias failing if the bias power supply caps become marginal, as welll as in the case of the 4650 and 5650 VFET gate stopper resistors as well as a few high-power resistors going open due to age and overheating (the latter can be connected with a design trade-off in the driver circuits of these amps). 8650, 5550, 8550 have a different output stage which dies not have these particular problems, but them 8650 and 8550 have dual main filter caps which can become marginal and are not easy to replace without some modifications. A search on this site and the web will disclose some service info on 4650 and 5650 amps which recomends replacement of some components in the protection circuits for better current limiting.
These amps were considered the high-end offerings (even the smallest 30WPC 4650 was signifficantly more expensive than the much more powerful but lower in the lineup 3650 BJT based amp), and are built to those standards - kind of like the difference between regular and ES Sony gear in later years.
Aside from that they do have a few known problems such as thermal transfer grease drying up, and potentially deadly problems with bias failing if the bias power supply caps become marginal, as welll as in the case of the 4650 and 5650 VFET gate stopper resistors as well as a few high-power resistors going open due to age and overheating (the latter can be connected with a design trade-off in the driver circuits of these amps). 8650, 5550, 8550 have a different output stage which dies not have these particular problems, but them 8650 and 8550 have dual main filter caps which can become marginal and are not easy to replace without some modifications. A search on this site and the web will disclose some service info on 4650 and 5650 amps which recomends replacement of some components in the protection circuits for better current limiting.
These amps were considered the high-end offerings (even the smallest 30WPC 4650 was signifficantly more expensive than the much more powerful but lower in the lineup 3650 BJT based amp), and are built to those standards - kind of like the difference between regular and ES Sony gear in later years.
I have noticed recently a couple of Sony ta 8650 v-fet owners commenting about the input /output clipping indicators flashing or staying on when the amp is playing at reasonable levels , I can only assume the independant gain controls on the rear of the amp have been turned up too high , overloading the pre-amp , try turning them down to give more headroom to the pre-amp , if it's the output clip indicator flashing , it could be overdriving and exceeding the rated distortion level , or DC at the speaker terminals , a check by a qualified V-FET expert would be a good way to go !
Hey glad to hear your TA-8650 is still going strong and giving you listening pleasure!
I wound up rotating out my reconditioned B-1 with a B-2 for the summer months since the B-1 runs hot and there's no AC in this old house making it already hotter in here than I can stand. I must say that the B-2 is such a superb sounding amp that I didn't really miss the B-1 ... but with that said I'll be moving the B-1 back into place soon (groan - I hope my back is up to it) since it's getting cooler and the B-1 deserves to be listened to too rather than just sitting there on my bench looking beastly. So for me it's B-1 listening from fall to spring and B-2 listening from spring to fall.
Regarding your TA-8650 running cool as compared to the 2 others you had; is it possible that the bias might be set a bit low in yours since V-FET amps generally run hotter than Class AB BJT amps because of the higher bias current required? Have you checked it lately to see that it's set right? You might find you like how it sounds even better if it is set low now and you adjust it up to spec ...
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Hey Yamahear great to hear from you again ! We V-FET obsessives need to keep the flag flying !!!!! We yes the bias was checked , also idle current ,and dc, it seems on spec , I have had a couple of comments "it's running too cool for an 8650 , but it is quite , powerful , and has heaps of grunt , so I'm happy , I think the easy speaker load I have could be one of the reasons , JBL speakers are an easy drive for most amps , mine are 6 ohms , I am actually listening to George Benson's greatest hits as we write to each other , This amp is freakish , it hasn't been touched in over 30years , and I pray that it doesn't fail , as trying to get any V-FET work done here in Perth Western Australia , would like flying to Mars looking for a Coke Can ! Fingers crossed the old girl stays alive !
Yes indeed!
If the bias/idle current was set a little too low you'd still have grunt and the amp would run cooler but the THD level would rise a bit ... or a lot depending on how far off it was ... but if you're happy with where things are now that's all that matters.
If it were mine and it was untouched for over 30 years, at the very least I'd be making sure that there's no nasty Sony VD1221 diodes hiding in there!
I have a customer's Sony TA-8650 on the bench now for recapping and troubleshooting a problem of weak audio in the left channel. On the analyzer, I see that it is actually a problem of no low to mid frequencies getting though.
If I take a heat gun to the BX-270 (IC103 buffer amp) for 5 seconds, the channel comes back to life with flat frequency response to match the good channel.
I'm concerned that this little green hybrid IC is bad. Even after recapping all the front end boards, this problem remains. Heat up the little green device package and channel comes to life. Not the sort of part I want to be hunting down!
If I take a heat gun to the BX-270 (IC103 buffer amp) for 5 seconds, the channel comes back to life with flat frequency response to match the good channel.
I'm concerned that this little green hybrid IC is bad. Even after recapping all the front end boards, this problem remains. Heat up the little green device package and channel comes to life. Not the sort of part I want to be hunting down!
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