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Repair WEGA V4810 / SONY TA5650 V-FET Solidstate Heaven By Helmuth.

hello friends

Well I have found what was the problem....I didn't turn the potentiometer enough.. I Know I Know, I'm not an elecktronic guy...Anyway I put the bias level on 50mV and start too listen. Well in fact its a tube like sound, but when the bias was on 0.1->1mV I had better resolution, better 3d, better separation, only bass was a littel bit smaler, but everything was almost better. Maybe it was better because of the my system character. Helmut turn down bias level and tell me how does it sound in your system. All this story gives me new knowledge about vfets and the bias. Well we can tune vfets changing the bias level- you should check this by your self. I think that bias level is the best when it is on the lowest level at once with distortions that doesn't improve.
 
Hi Intuos

I just placed some more MKS capacitors I have all capacitors up to 10uF replaced with a Wima MKS 2 type. More resolution in the sound. and placed a 0.47uF under the 1000uF parallel.

The bias must be checked between the + of the Left or right speaker output and the bias tab of the left or right channel, next to the potentiometer.

I do not want to have more crossover distortion so I leave it like it is 50mV=150mA. It can only be better then low current.

Regards Helmuth
 
Helmuth said:
It can only be better then low current.
Click to expand...

Well, above the specificatrion I always use my ears
many times when I was making some tube amp with my friends which is a tube constructor, I was as a listener and I was making a sound revision and I must say that in audio many thing look different than on paper, and different voltage on the heater and net make a big improvment to the standard specification.
So try :) but it is your decision.


about the recaping I am slowly geting on it.
 
intuos said:
which is the preamp board in wega?
Click to expand...

The boards mounted on the front next to the volume knob. First remove al knobs and the front plate.

And left the board with the switches. The MKS2 you cant get up to 100V but in the signal path it isn't a problem there is no high voltage. The Sony designer choose High voltage to prevent leakage current sounds I think.

MKS2 50V /63V will do fine they even got a self repairing effect in them so they are very good only do not make them to hot with your soldering iron because they do not like temperatures above 100 degrees.


Watch out there is a 3u3 cap 100V of the riaa amp powersupply that one needs to be 100V! When I got it right C106.

Regards, Helmuth
 
intuos said:
hello friends

....Anyway I put the bias level on 50mV and start too listen. Well in fact its a tube like sound, but when the bias was on 0.1->1mV I had better resolution, better 3d, better separation, only bass was a littel bit smaler, but everything was almost better. Maybe it was better because of the my system character. Helmut turn down bias level and tell me how does it sound in your system. All this story gives me new knowledge about vfets and the bias. Well we can tune vfets changing the bias level- you should check this by your self. I think that bias level is the best when it is on the lowest level at once with distortions that doesn't improve.
Click to expand...


Hello Intuos,

I checked with low bias some time ago my Sony TA5650 and did distortion measurements with oscilloscoop because there is so much confusion in the forums.
Below 28 mV bias no visible distortion under severe test conditions. I use now 30 mV, but because of spread in components it is probably wise to use little more (sony latest advised 50mV). With low bias, sound was defenitely of less quality in my set.
For details see: http://audiokarma.org/forums/showthread.php?t=74078 (nr 12 dd 16/6/2009)
Because of your good listening experience with 0 mV bias and degrading sound with bias, i would expect some error!
With help of an oscilloscoop you can see what is happening. Without i would measure Hfe of transistors and look for partially faulty ones.

regards,
Piet,
 
RealWorld said:
Hello Intuos,

I checked with low bias some time ago my Sony TA5650 and did distortion measurements with oscilloscoop because there is so much confusion in the forums.
Below 28 mV bias no visible distortion under severe test conditions. I use now 30 mV, but because of spread in components it is probably wise to use little more (sony latest advised 50mV). With low bias, sound was defenitely of less quality in my set.
For details see: http://audiokarma.org/forums/showthread.php?t=74078 (nr 12 dd 16/6/2009)
Because of your good listening experience with 0 mV bias and degrading sound with bias, i would expect some error!
With help of an oscilloscoop you can see what is happening. Without i would measure Hfe of transistors and look for partially faulty ones.

regards,
Piet,
Click to expand...

Hello Piet,

Probably my home set play better on this value of bias. I was chcecking 5mV,10mV,20mV and 30 also. The best is with 0-5mV, I dont know why it is so.
But without a doubt with value of 0-5mV this amp bring me the sound of big,huge 3d scene, with lot of details, I just love it. Well this bias was put by service so I don't know why they did it with bias on this level.
With bias on 30mV the sound was much more warm, tube like, but the 3d scene and details started to hiding, that's why I left it on level that was before(service put). Maybe every thing will change when I recap all unit.

regards,
Tom
 
hello everybody
after long time of my absence I finally recaped all device. Two big capasitors are now Nichicon Gold Tune 15000uF 80V-prime series, bypassed with 1000uF Nichicon muse KZ 1000uF 50V and bypassed with PIO capasitor 0,5uF(polish army stuff). All section of pre amp supplay are recaped wit nichicon muse KZ with original capacity.
The pre amp signal capacitors where changed with PIO MBGO capacitors bypassed with teflon capcitors.
The power amp section also were changed with Nichicon Muse KZ capacitors and with film capacitors.
Amp with new capacitos have been working for only about 20-24 hours.
everything seems to be better, speciale bass- WOW! More air, better seperation, airnes. The more hours it plays, the better sound comes form it.
Fotos coming soon.
 
and one subject more- 3d and space.
The space and 3d image are just incredible, one of the best from this what I have heard. For example yamaha cr2020 is at liest one class down in sound presentation vs wega 4810.
VFET MAGIC!!! :)
 
Fixing a TA-4650

You probably all know that you can buy Vfet's on Ebay.
There are several vendors who have them.
Since I bought a defective Sony TA-4650 amp I had to purchase two pairs from a Honk Kong dealer Jim's Audio. When I got them it turned out not being pairs at all. The amp had large offset voltage on the speaker outputs (200-300mV) and the B2 voltage was out of balance. At that time was an other dealer in England (Littlediode) who sold 2SK60-s (no pictures), so I bought two from them. When they arrived, it turned out not being Sony's, but had a Hitachi logo on both. I made some measurements on all and also on an original Sony SK60, which I removed from a TA-5650 amp and which I'm owing from day one. The way I compared them to make a simple source follower choke loaded stage and drove it with a clean 1kHz signal from a Philips Cd player headphone output (max 4V out). The Cd with a 1kHz signal was made with the help of Cooledit 2 and the result was observed with a help of a HP analyzer. The signal coming from the CD player was free of harmonics ,as much I could see on the HP analyzer.
In the picture you can see the bias voltage needed for the 1A current, and the drive voltage needed to achieve the 2.2V output on the 8 Ohm load. The spike at 7kHz is from the returning track from the player.
 

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Repairing Wega JPS 350V

Hello guys, I am new on this forum, and what got me to this site is the fact I tried to find out more about my vintage Wega JPS 350V amplifier. I know Sony made almost identical versions of their amplifiers under Wega logo, but I really couldn't find out exact version of Sony amplifier that is exactly the same as Wega JPS 350V. Closest "candidate" is Sony TA-11, but this one have more options added to the design. Reason why I need that information is repairing that amp. When amp is on, light comes on, but no sound at all. So far I found one open fusible resistor, replaced it, but problem still exists. I even desoldered four transistors in power amp stage (Sanken 2x 2SC1986, and 2x2SA771). All four seems to work fine (or I'm wrong?). Forward voltage on each pn-junction is around 0.45V. In opposite way DMM shows "OL". But I expected more voltage, for example 0.6 or even 0.7V. Does this mean transistors get weak or are they just ok? When I use headphones I could hear something, only when I crank volume to the maximum. VU-meters don't work, there is just a light, but that's all. On the output transistors, before I desoldered them, was a voltage of about 42V, on the base and emitter, and on collector almost nothing. Two transistors had same positive voltage, and other two same negative voltage.
It's difficult to troubleshoot without even block diagram. I tried to connect sine wave and to trace it through and watch on my oscilloscope, but I couldn't find where I lose signal. I think it's somewhere between volume pot, and differential amplifier. Also strangely, I determined that I lose signal on the other end of one resistor. Remove them, and found that resistor have proper value, so I soldered it back. Most of the fusible resistors checked on board, seems to have ok value. Also cement ceramic resistors MPC2 0.47x2 seems to be fine.
So does anyone know what Sony service manual I should find?
Any kind of advice is much appreciated.
Thanks in advance.
Edit: I managed to repair amplifier without service manual, it turned out to be only resistor problem! I replaced 10 of them, half of them had wrong value, and other went open.
 
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