Sony TA-5650 - To switch on or not to switch on?

[MichaelThwaite]

That is the question.

I picked up a nice vintage amp in 1999 from a shop in Harrogate - 'cause we all knew the modern ones would stop working come the millennium 🙂

It's a tidy, clean TA-5650 (sn:601683), in OEM box and even has the wood side panels. I used it as my computer hifi through to about 2015 - never gave it a thought other than that it looked great, and sounded pretty good too.

It went into a cupboard in about '15 and it's now 2023 and I'm reading about suicide diodes and impossible to find JFETs and was going to plug it in but lost my nerve!

Given that it probably works fine, how can I be sure before I plug it in? Has it already been updated with new diodes, capacitors, etc. How can I tell? Can you all tell?

I've enclosed some photos in case there are some obvious tells, like the JFETs are a bit messy and HG-53 which looking around I'm wondering if it's a tell?

I really appreciate your experience, I can solder stuff and even own a hand-held oscilloscope but, I'm in a different pool here!

MPT



FYI: I can't register an account on HiFiEngine to get the manuals as I have the wrong everything.

 

[Indigent Audio]

Of course the right thing to do is ship it to me so it can be properly tested…it’s rare and valuable, dbt, scope or taking it to an expert all seem reasonable

 

[MichaelThwaite]

I'm certainly not opposed to that, might be pricy as it's very heavy as you may know. But PM me, I'd like to understand my options, thanks.

 

[madis64]

You will find the downloadable service manual at elektrotanya.

Taking a quick look into it - it seems to have some unusually high voltage power rails (97V by the schematic) and some only 100V rated lytics on these.
These lytics have been out of use for 8 years now - with blunt powerup I would say your luck may vary 🙂

 

[rayma]

Get a Variac and power up slowly and gradually, over perhaps 30 minutes or so.
You could combine that with a bulb tester, in case of a sudden problem at near full line voltage.
But either one does not take the place of the other.

 

[Indigent Audio]

Lots of experience here, an expert will chime in. Be careful of advice which involves harvesting v-fets for other (class A) designs

 

[MichaelThwaite]

You will find the downloadable service manual at elektrotanya.

I passed the test and got that one, thanks!

Get a Variac and power up slowly and gradually

I think I've read that the variac route may be problematic with this amp, not sure why, perhaps something to do with biasing the v-FET's and some kind of inversion!

I'm thinking that there's a diode fix but can't seem to pin down the details. I'm also looking for an opinion on re-capping.

 

[MichaelThwaite]

You will find the downloadable service manual at elektrotanya.

Sorry, I forgot to add, I'm looking for the service bulletins, I think that they have the diode patch and some advice on biasing. ElectroTanya doesn't have the bulletins as far as I can tell.

 

[rayma]

Here's a tech's experience with these, and some service bulletins.
If there are known issues using a Variac or a bulb tester with these, then do not use them.
https://retrovoltage.com/2015/03/04/sony-ta-5650-full-re-cap-and-adjustment/

 

[madis64]

I'm also looking for an opinion on re-capping.

A teaser (results from speaker terminals):

- an amplifier from mid 70-ies, full re-cap, all switches cleaned, signal path lytics being 10 uF and less replaced with film caps.

Measurements done with a sound card and RMAA software so they are not "academically accurate" but the change is visible.

 

[MichaelThwaite]

Here's a tech's experience with these, and some service bulletins.

Thanks, he found his variactor diodes had already been replaced, have my Variactor diodes already been replaced?

Looking at is that stock - that's thermopath on there?

A teaser (results from speaker terminals):

That's compelling! The drop in the noise floor is enough! Thanks.

 

[rayma]

Check the part number on the diodes and compare with the service manual.

 

[MichaelThwaite]

Check the part number on the diodes and compare with the service manual.

I've actually gone ahead and bought a complete set of diodes for the varactor diode replacement and the PSU mod... That's $1.50 I might never see again.

 

[ElArte]

WOW. How much we have advanced in so little time!

 

[MichaelThwaite]

WOW. How much we have advanced in so little time!

Yes! I know, I've spend hours and hours following threads trying to get my head around the various options but, actually, just posting and listening to your comments and following the links has kind of solidified the mission as it were into some manageable steps; get parts, open unit, check/do known fixes, follow service manual.

... I'm feeling pretty confident 🙂

(Oh, and sorry to the mods, I'm a new account so everything has to be approved... thanks guys, appreciated, been there, done that, have the scars!)

 

[rayma]

I've actually gone ahead and bought a complete set of diodes for the varactor diode replacement and the PSU mod... That's $1.50 I might never see again.

Hopefully they're from a known, reliable vendor, and you will test them before installation.

 

[Citizen124032]

No variacs or dim bulb test with these amps, or the v-fets are destroyed instantly.
The very problem are the dual-diodes, four of them in the 5650 (three in the humble 4650), to be replaced by two serial 1N4148 (or alike) ASAP-NOMATTERWHAT.
Then the caps in all the supply lines, the swept up hv-supplies first of all.
That very supply modification is fruitfull.
Also, depending on the serial number, grounding issues can happen but leave it as is if the amp performs right.