Sony TA-4650 integrated amp

[Kenneth Swauger]

Hello,
Here's a classic Sony integrated amp that uses V-FETs for the output devices. This one belongs to a friend that had not been able to get it working. I had to source 2SK60 and 2SJ18 matched pair transistors from Hong Kong. The DC bias had malfunctioned and blown one of the original 2SK60s. I used 1N4148 as replacements for the bias diodes and some new coupling caps (Black Gate) and Panasonics. The ESR meter was a great help in checking out the caps. Some overall cleaning and a listening test with an SACD player and a pair of LSi7. Talk about a sweet sound? Very listenable, I hope he's not in a hurry to get it back.
Enjoy, Ken

[polkatese]

Very nice and beefy looking vintage Sony. What is the specs Ken? circa 1980?

[jon s]

Ken,
I have a couple of TA-4650s which are somewhat working but in need of service. I am thinking of tossing them if you are interested. One has crosstalk issues (if you have the tuner on, you can hear the signal thru the phono stages) and the other works but i believe the bias diodes are bad, one of the speaker terminals is busted... the problem is that i live in Hawaii and shipping them anywhere is very expensive... as you know, these amps are heavy for their size.

I am currently using their TA-8650 V-Fet amp, rated at 80wpc which was worked on by EchoWars of Audiokarma.org. Cost me $300 in parts and $500 to ship back and forth to Kansas.

Polkatese, the amps are rated at 30 watts per channel. They are from the mid-70s. V-Fets were expensive output transistors which only Yamaha and Sony made of some expensive amps.

[Kenneth Swauger]

Hello,
It was designed to produce 35 watts/channel with dynamic power as 90 watts/channel. The THD was less than .1%, which is what I measured. The V-FET was a way to produce a solid state device that had a similar operating profile as a vacuum tube. They are very hard to find and need to have a closely matched Vgs to work properly.
There are very few coupling caps in the circuit and some seem to be film type. there is a slight channel imbalance, probably in either the volume or balance tracking. The tone controls have a "cancel" button to take them out of the circuit path.
There is a "bigger brother" to this amp, with four V-FETs per channel. It would be expensive to replace all of those.
Ken

[polkatese]

Very nice. thanks for the info.

Ken, the inside looks brand new. What a labor of love!

[Kenneth Swauger]

Hello Jon S,
This is my first time looking at a V-FET amp. I've been helping out a few friends, getting a classic Marantz tuner working. Also an ARC LS3 muting stopped working and some Moscode items. There's a Nak cassette deck next in line. Outside of the un-obtainable power transistors the Sony was fairly straight forward. I like learning about things as I try to get them working.
Mostly I flip Revox decks as a way to keep out of trouble.
Ken

[Kenneth Swauger]

I discovered a new method for getting the outside of a component very clean. I used a very lightly dampened paper towel and a squirt of Dawn liquid dish washing soap to wash the AC transformer, front faceplate and rear panel. Then wiped off the soap with another damp cloth. I removed the control knobs and brushed them with a toothbrush and Dawn and really got them nice and clean.
For the circuit boards I use a lot of Q-tips and Googone and go around each part carefully.
But the Dawn worked well.
Ken

[Kenneth Swauger]

Hello Jon S,
I've been thinking about the signal leakage you mentioned in your Sony amps. I noticed that there was a shorting plug in the "phono 2" inputs. If you're not using a turntable to either of the inputs try putting a shorting plug into them. That should prevent hearing the tuner through that input.
I just checked the DC bias and it was still around 75mV after three hours of playing. The bias diodes are "heat sinked" to a nearby transistor with heat sink compound. I guess they can drift if they get too warm.
Ken

[mhardy6647]

Nice and not terrifically common amplifier.
You know of the Vintage Knob, yes, Ken? :-)
http://www.thevintageknob.org/SONY/s...650ST3950.html
(closest Axel has is the TA-3650)

[Kenneth Swauger]

Ah, yes. That is a very well done site, some beautiful gear there.
Ken

[geebolt]

I still have a TA-5650 I bought new but haven't used in years.. Rated at 50 watts per channel. And I can attest to the great sound the V-FETs are capable of. Someday I may have to put it back into service...

George

[Kex]

I discovered a new method for getting the outside of a component very clean. I used a very lightly dampened paper towel and a squirt of Dawn liquid dish washing soap to wash the AC transformer, front faceplate and rear panel. Then wiped off the soap with another damp cloth. I removed the control knobs and brushed them with a toothbrush and Dawn and really got them nice and clean.
For the circuit boards I use a lot of Q-tips and Googone and go around each part carefully.
But the Dawn worked well.
Ken

Reported!

For spamming!

http://www.dawn-dish.com/en_US/home.do

C'mon! Admit that you own a boat load of stock in this!

[hearingimpared]

Ken that is a beauty! I love that vintage look and it appears to be a heavy sucker.

[Kenneth Swauger]

You found me out! I invested my complete 401K in stockpiling Dawn liquid soap. Please, everyone, clean all the stereo equipment you can! How about a National Clean Sound Day?
:o

[billbillw]

Ken,
I've always been curious about trying out one of those V-FET Sonys. They often sell relatively cheap, and I like the style, but I have fears of expensive paperweights if the output trannys go bad. I always thought those replacement V-FETs were basically un-obtanium. I guess you have connections.

[Kenneth Swauger]

Hello,
Yes, the Sony is pretty substantial, 25lbs according to the service manual. Mostly metal in the chassis construction, especially the heat sink and AC transformer.
The Sony V-FETs are pretty difficult to find. I first tried a supplier in England but that didn't work out too well. I finally went with an electronics supplier listed on eBay and that was better. A pair of output transistors was $70.00, so not a light expense.
If you have an older unit I would recommend having the bias diodes replaced and the power supply and amplifier circuit board caps checked. Also, don't allow the amp to be used with a Variac. The gradual increasing voltage could cause the output devices to malfunction. Also, in all likelihood, the thermal compound that allows the excess heat of the output transistors and the heat sink should be cleaned off and replaced and the isolation gasket replaced if needed.
Kind of like hugging a porcupine, tricky at best.
Enjoy, Ken