Sony TAN-5550 ancient VFet amp, can I just turn it on?

[Pruimenvlaai]

A friend gave me this amp, hasn't been used in years. Can I just turn it on or will I need to measure the caps etc. first so I don't blow it up? What are the risks? I'm an amplifier noob so I don't really know what I'm doing, all thougths appreciated!

 

[JonSnell Electronic]

It would be a good idea, with no inputs or loudspeakers connected, to put a 60Watt tungsten filament lamp in series with the mains to allow for current limiting. If after say half an hour the lamp is out or very dim, try full mains. If the lamp is full brightness, you have a problem somewhere.

 

[Welcome]

The vfet amps tend to have serious problems that need sorting out, else the vfets will eventually blow up and there is no way to repair it then.

It's a widely covered subject, so I suggest you simply google it.

 

[ilimzn]

It would be a good idea, with no inputs or loudspeakers connected, to put a 60Watt tungsten filament lamp in series with the mains to allow for current limiting. If after say half an hour the lamp is out or very dim, try full mains. If the lamp is full brightness, you have a problem somewhere.

WILL YOU FINALLY STOP GIVING 'ADVICE' WITHOUT LOOKING UP FACTS!!!!
Powering up a VFET amplifier with a 'dim bulb' setup WILL, I repeat WILL BLOW UP THE VFETs.
And when they do, I sincerely recommend that the author of the question bill you for the 8 that will die, which, IF you are lucky, will cost you $50 a piece.

Now for the real advice:
It IS possible to power up the amplifier without the VFETs fitted and check out the VFETs as well as the relevant voltages to know if it will work. It is NOT trivial (needs some clever mechanical tricks as the VFET screws also hold the power amp PCB), but it can pass enough signal to drive a set of headphones with which the basic functionality can be checked.

There have been many threads here and also over at audiokarma.org, regarding all the Sony VFETs...

 

[miklos]

Normally yes, but first you have to change the biasing diodes D501, 502, 601, and 602. Replace them with series connected regular silicon diodes.
Than adjust the bias to 25mV on the V-Fet source resistors, or 20-25 Celsius above ambient temperature. Some amps have smaller heatsinks.

 

[joshvi]

Be care full ! V fets are difficult to get. First remove the bottom plate. you can get access to the V fets. Remove and check them.Do you know how to check V fets ? V fets are depletion mode devices so very low resistance between source and drain.But between G-S and G-D shows as diode. If all the v fets are okay check the power supply voltages before putting the vfets back.

Service manual from here. Sony TAN-5550 Stereo Power Amplifier - HiFi Engine

Today repaired my sony ta4650. Smaller brother of ta5550. Very nice sound

 

[east electronics]

WILL YOU FINALLY STOP GIVING 'ADVICE' WITHOUT LOOKING UP FACTS!!!!
Powering up a VFET amplifier with a 'dim bulb' setup WILL, I repeat WILL BLOW UP THE VFETs.
And when they do, I sincerely recommend that the author of the question bill you for the 8 that will die, which, IF you are lucky, will cost you $50 a piece.

Now for the real advice:
It IS possible to power up the amplifier without the VFETs fitted and check out the VFETs as well as the relevant voltages to know if it will work. It is NOT trivial (needs some clever mechanical tricks as the VFET screws also hold the power amp PCB), but it can pass enough signal to drive a set of headphones with which the basic functionality can be checked.

There have been many threads here and also over at audiokarma.org, regarding all the Sony VFETs...

Please dont get upset with John ...he is been told many times before for similar issues ....some things will simply never change ...

Repairing above 1000 audio machines per year this the only thing we NEVER DO the minimum will be a visual inspection for capacitors and soldering issues before even think on powering up .

Machines that operate in higher bias than typical a few ma consumer amplifiers do , simply NEVER !!! Expect 100 timer more troubles in high bias machines ...

 

[miklos]

Pruimenvlaai I don't know how far you come with the switching on the amp, but I would listen to what ilimzn said. This is not about low or high bias, this is about the correct bias being there when the output stage gets his power. The v-fet is a depletion device, without the bias it represent a short to the B+, that's why would it self destruct.

 

[Zen Mod]

frankly ..... that amp is not bite to swallow for novices .........

either bring it to someone with proper and adequate knowledge , or toss it directly in dumpster

I made service/restoration on few of them , spent enormous amount of energy just cursing previous butchers and experts

 

[east electronics]

Frankly ?

 

[miklos]

dumpster?
if they still good only the output transistors worth over $400

 

[Zen Mod]

que?

 

[Zen Mod]

what I intend to say is - result is the same - ignorant repairing that amp , or tossing it directly to dumpster

isn't that obvious ?

 

[Pruimenvlaai]

Okay, it'll have to sit on the shelf until summer holidays, when I can really dive deep into this subject and do some maintenance/repair before turning it on.