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Technics SU-VX800

Stereo Integrated Amplifier (1991-92)

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Technics SU-VX800

Specifications

Power output: 110 watts per channel into 8Ω (stereo)

Frequency response: 20Hz to 20kHz

Total harmonic distortion: 0.007%

Damping factor: 80

Input sensitivity: 0.25mV (MC), 2.5mV (MM), 150mV (line)

Signal to noise ratio: 67dB (MC), 79dB (MM), 100dB (line)

Channel separation: 50dB (line)

Output: 150mV (line)

Speaker load impedance: 4Ω to 16Ω

Dimensions: 430 x 158 x 429mm

Weight: 17kg

Year: 1991

Price: GBP £450 (1991)

Downloads

service manual  English

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Comments

Solving heatproblem at Q652/Q654 in a Technics SU-VX800

Q652/Q654 was never moutetd on a heatsink - a major problem and big mistake. I opened some of theese (very good) Amps and it's always the same. Q652 /Q654 got so much hot, the pcb looks more ore less burned. And the soldering of these both suckers got bad, because of the heat. The other day a friend had one of theese Amps with a pretty much burned and smelly board to repair at my house. Even my VX800 board looks slightly roastet. It is my Spare-Amp, usually i run a BOSE 4401/1801 Combi with four 901 Speakers. But i like this Technics very much, if it did not had the heatproblem it was a perfect and strong Amp. So what to do? I got some Fischer Heatsinks they look like made for this problem. So i mounted one on the board with a 35mm thread bolt. In the back of the heatsink i made a connection to the main Heatsink - yust for stability, then i mounted all 4 Transistors (Q651 to Q654) on the Heatsink and with short wires i connectet them to the original connections. While i did this work i thougt about putting all the IC's on sockets and put some threads in the main heatsink to mount the transistors. I don't like this kind of self tapping screws which was originally used. Allright so i took some more time and did some more repairing including resoldering this poor soldered board.
Then came the test: Steve Miller "Macho City", Volume half turned on. Fun even for the neighbors.
Yeah! this is it. The little Heatsink went to 62°C and is stabile, everything works fine.
So I put some pics into the gallery if someone want to do this very important job too. For those who want to know more and more pics - mail me.

Greets Richard

re: Solving heatproblems in a Technics SU-VX800

... and it goes on!
After removing the frontplate came another big surprise.
6 peaces (each 1,5 Watt 1,5KOhm) resistors (2 in a row) are producing a lot of heat. So much, the pcb is almost coal! They are current-limiters for zener-ziodes and have a 1,2W (59.9V/3000Ohms*0.02A) load. So far-so good and electrically was 1,5 Watt resistors allright. The problem is the area behind the frontplate. There is no air-flow and so theese resistors can produce lots of heat which is hangin' around at the same area. If all of this three zener-diodes have the same value, there will be a solution with a single zener and a transistor (power zener) on a heatsink, because there will be no more chance for soldering - the board is to crunchy. And while there are 59.9 volts there is no chance for just some regulators (most of them do 35 volts max.).
If the zeners are not the same value, so there will be a power-zener with 24 volts and after that comes some line-regulators - we well see.
The work goes on...

Greets Richard

next testing music will be Lynyrd Skynyrd : that smell ;-)

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