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Purchasing Sony ST-A6B - please help

sheiku

sheiku

Member
Hi ,
I can buy from an a local private seller an Sony ST-A6B for about 130 euro.
I asked him to make a demo for the functionality.
It seems that a lot of lights or bulbs do not light.
It is so bad? Can be replaced easy? i am handy at recapping and soldering.
But my main concern is to work fine in stereo mode, and also to lock the stations and not to loose the locking station, because i do not see the stereo led lightning
Just as a story , i received in the past an double mono tuner for a seller. One channel was dead and he wired the dead channel from the " alive" channel.

In the video the seller told that he do not have any antenna coupled at the back of the tuner.
please see:
and



Thanks for any thoughts..
Dan
PS
I was in searching for a Sansui but the prices for TOTL or second position from the top are ....huge and increased day by day..until i found this sony with very few but positive reviews.

all front pannel and dial line must be lighted like in the picture:
ST-A6B.jpg
 
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Hello
I cannot say if the bulbs are easy to replace but I can read that this is a good tuner.
Go to the middle of this page: https://www.fmtunerinfo.com/sony.html
Also here: http://www.thevintageknob.org/sony-ST-A6B.html
Do you have access to a technician that can do the alignment after you fix the bulbs and change some capacitors? A tuner of this age (1978) will need an alignment for lowest distortion and best stereo reception and separation.
some modifications suggestions : https://www.fmtunerinfo.com/DIY.html#ST-A6B

good luck
paba
 
Thank you ,
I did not resisted and i ordered it..after an short negotiation, with 120 Euro
In 2-3 day i should receive it... hope God help me to be in good condition.
Regards,
 
Tank you paba,
For changing capacitors or other components including mods ( but with clear instructions) i will do the work. I made the recap in the past with success to some sansui big amps.
But i do not find no one in my all country to do an alignment. I searched on interned for about 2 years an technician and no one to find.

So I am preparing this week am order for capacitors and other components to recap most of my tuners..

i have an
Sansui TU-x701
Mitsubishi DA-F20
Hitachi FT 8000 ( and i am waiting the ST-A6 Sony)

all sound very GOOD to my ears, BUT , i have an Sansui TU-217 ( the bottom position in the line) and strange it sounds almost better:
>absolutely identical with Mitsubishi DA-F20 ( in blind tests i canot tell wich is)
>better than Hitachi FT 8000 ( mitsu sound a little boring, liniar, no 3d )
>and a little more involving than Sansui TU-x701 !!
but ...Sansui TU-217 have the worst sensitivity from all
So , my conclusion is that ( maibe) sansui was restored by the previous owner and the other are not recapped and not realigned.

Recapping is easy for me , but the realigning is impossible.

Thank you all
I will post when i will receive the sony to tell my impressions
 
You have a good set of tuners, not sure you need another one :rflmao:but we always get just one more. :banana:
Maybe what your ears want is a tube tuner, if you find all those a little lifeless or flat or they all need alignment and maybe fresh caps in the signal path of the circuit.
I assume the signal is good at your location (antenna?). But you know FM stations broadcast crap and then they process it with extra loudness and compression of dynamics. See if you have at least one station that exercises care in the post processing and also selects music that is well recorded.
 
Oh paba...i promise this will be the last. :)
I will try to improve what i have with fresh caps. If i will not have good results i will sell some of them. And i will switch to internet or HD radio.
And i plan to buy an tube preamplifier..maybe i will have another sound.
Anyway in my region i have about 15 radio stations with good signal and some with excellent signal. And almost no HD radio. And internet radio even is flat and compressed when i do comparition with FM even on 128kbps or more. And i do sometimes AB testing
Thank you all
 
So, i received the Sony. Quite disappointed:

Very bad packaging.
In 9/10 estetical shape. 3 minor scratches on the aluminum front visible from close look

BUT things i discovered that are not working:
1) the tuning needles (or the "VU metre" - the second from the right) is not working. It is stuck at 4 o clock not six/down and it is not moving at all. On the demo video it was working so i think it is from the transport.
2) All the upper leds are not working . I do not understand why because at least the SIGNAL led from the signal Vu metre was working on the demo video. So the only working bulbs are on the scale.
3) the most bad news : cannot hear STEREO.
let me explain how it sound: better than my unmodified Sansui Tu-x701. It have more air, better high, more 3d i feel. Sansui have more bass i feel. But I also hear that on one channel the medium and low frequencies are not so good. So it certainly need an recap and i will do it.
But when i listened on headphones i hear no stereo sound. On the commercials on Sansui i hear sound moving different from left to right but on sony no ..just double mono.
there is a solution for that?
NOTE: Hard to receive stations are easily received with Sony. So it is more sensitive than Sansui. But it shows with the same ( long wire antena) that the signal is weaker. let say 3/5 on sony and 5/5 signal from sansui.
Inside there is now trace of intervention. No soldering sign.
This is the second tuner i bought with same symptom: double mono, even on strong signals on Sony let say 4 / 5 as signal i have mono. I canot tell what the stereo led is tell me because all leds are not working.
i have no one technician to repair it. Only me , my soldering gun and my ohmetre.

Thank you all

PS for other with the same problem: i found yesterday about some similar cases with no stereo on vintage tuners. I found no help but there are some sollutions proposed
1) the stereo mode will fix after an complete recapping
2) there is a trimpot near the Fm Multiplex IC.. FM MPX IC for stereo separation ! ( must go deep on this idea) here https://audiokarma.org/forums/index.php?threads/fm-but-no-stereo.662632/
and here https://www.audiokarma.org/forums/index.php?threads/sony-str-v6-stereo-fm-lamp-wont-light.472603/

PS2: i followed your tips regarding the cleaning and i cleaned the FM gangs and al the knobs and switches. No stereo , but there is an improvement because there is less hiss between stations.
 
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Good luck! I hope your ambition pays off well. Please post some photos when you can! Thanks!
 
@sheiku
If you don't have it yet download the service manual. I just took a very quick look and I suggest you adjust the variable resistor RT-301 until you have a nice 19 kHz signal present at the 19Khz test point (near pin 12 of IC 301). The PCB should be labelled. Do this while tuned to a station you are certain is stereo and with an antenna to get the strongest possible signal. Stereo bulb might be burned or have issues, but if you get 19Khz at this point you know something. That variable resistor or pot might have drifted so the chip no longer has a good PLL lock.
Nearby is another pot RT-302 which is to adjust the stereo separation. Don;t touch that unless you know how to adjust for max stereo separation. The manual suggest a procedure but you can only do this step when the MPX is decoding stereo first.
good luck
/Paba
 
paba said:
adjust the variable resistor RT-301 until you have a nice 19 kHz signal present at the 19Khz test point (near pin 12 of IC 301). The PCB should be labelled. Do this while tuned to a station you are certain is stereo and with an antenna to get the strongest possible signal.
Click to expand...

With respect, I don't think this is a valid way to adjust the PLL free-run frequency. If using a frequency counter, the adjustment should aim for 19KHz with NO signal (or with a strong un-modulated signal from an RF generator, which I think is a little bit better technique).

If adjusting "by seat of the pants" with no frequency counter, then just set the adjustment to the middle of the range in which stereo reception is enabled. If there is no stereo reception for any setting, then something else is wrong.
 
@chazix I assumed the owner doesn't own an RF generator or a generator of any kind but maybe owns a low cost digital multi-meter that counts frequency. The Sony service manual actually suggests as an alternative method the over the air signal as a source. So yes there is a better way but over the air gets you close. right now he has no stereo so at least he will have stereo potentially if the unit doesn't have other issues.
 
There are variations on setting the FM MPX VCO...most tuners require no signal at all to set the pot via frequency counter. However, a few require a strong signal, but no 19 kHz pilot, to set the frequency correctly with a counter.
In general, using a strong "off the air" stereo signal, and slowly rotating the VCO pot adjustment completely both ways will tell you if that is the problem. If so, you can proceed from there to set it with a counter, or proceed to adjust it similarly with a weak stereo station - to get it working under all conditions.
I have worked on 2 or 3 of these ST-A6Bs, but it was a long time ago. My recall is the stereo light bulb is part of the circuit that activates the stereo function- and the tuner does not activate stereo with a bad bulb. You could try using a good lamp from another function (like IF wide or narrow lamps) to test it. Test the bulbs resistance - if open, it's bad.
I think with some testing, one could develop a resistor / LED circuit combination to replace the bulb, and make stereo work, but never tried that myself.
 
I looked at the over-the-air procedure in the Sony manual. Seems to me that it is pretty much the same as what I described as a "seat of the pants" procedure. Specifically, it does not call for a frequency counter.

The reason a counter isn't needed is that, if the PLL is able to lock at all, then its oscillator will be running at 19KHz by definition. (Or rather, the PLL oscillator will be running at the same frequency as the over-the-air pilot frequency - but that had better be 19KHz!)

I'm glad I took a look. I like Sony's description of the over-the-air procedure enough that I think I'll just refer to that instead of trying to describe it myself.
 
Agreed, the method by chazix is great, same procedure as I recommend on my LM4500 website. It's pretty universal for any FM tuner that uses a MPX chip with a VCO adjustment.
The ST-A6B procedure is below, they show both methods.

The MPX chip 19 kHz lock curve width is dependent on the amplitude of the composite signal w/ 19 kHz pilot. For weak stations, the composite output from the detector (including the 19 kHz pilot) is usually lower in level, and if the not adjusted at the center of the lock curve, may not work in stereo. Using a counter will guarantee it's centered on the pilot lock curve (this is published in the MPX chip specs). But testing with a weak station usually can also work, provided the tuner allows stereo for weakish stations.
 

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wowww..many technical information and help.
Thank you all.
because i do not speak natively english i have to stay a little to read and to understand corectly what you wrote. And after that i will test and answer you

Thank you all again
 
Thank you all.
i have all the sony manuals and i found on the PCB the variable resistor RT-301 also the 302.
(@ paba )
I will read again the adjustments indication to be sure not to do something wrong..
i will came also with some picture.
Thank you

ps
Bob@FM i have only the dial bulbs working , not other bulbs. Can i use one from the dial?

33.jpg

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I am mostly going from memory here - My recall is no, the dial panel bulbs are different size and rating from the wide, narrow, and stereo bulbs which are small narrow bulbs.
It's been maybe 10 years since I was inside this one.
 
Ten years and you have a great memory @Bob@FM yes, today i checked and you have right in every detail.
I will search an alternative.
Thank you
 
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