My Vintage Collection: Time for some Housekeeping - or not?

[Family_Dog]

Me, Jan 17th 2015:

Sadly the amp is lying in pieces on my workbench




It played absolutely perfectly for about a week, then kept cutting out and going into protection. Traced various faults, one of which amazed me somewhat, somebody had fitted a NPN transistor (2SC640) in place of a high-voltage PNP one (2SA1124) in the power regulator circuit. But it still worked, strangely enough. Not having a 2SA1124 transistor I used the closest thing I had, a NTE159. Same problem, the amp stayed on for a while and then randomly went into protection mode.



Q312 was fitted, different lead lay-out hence heat shrink on legs to prevent short-circuits.

Tracing the speaker-protection circuitry - and here I was very ably assisted by my partner at work, who is an electronics fundi (I grew up on valves, not pieces of sand) - we came to the conclusion that the TA7137P IC had an internal fault where the final stage had an intermittent open-collector status and its output was going high intermittently, thus enabling the speaker-protection relay. Proof of the pudding was the fact that there was nothing triggering it to do so as those voltages were spot-on. By earthing the IC's output, I could bring it out of protection. But now I had no speaker protection!



The IC (Q551) is obscured under the two blue & one orange wires bottom left of the pic (of course, whoever said it would be easy!)

Frantic e-bay searching web-searching eventually led me to a local supplier who had just one IC in stock, as well as 2SA1124 trannies, so I am hopeful that by this time next week, the Technics will be its usual chirpy self again!

-F_D

 

[Family_Dog]

Me, Jan 17th 2015:

Sadly the amp is lying in pieces on my workbench



It played absolutely perfectly for about a week, then kept cutting out and going into protection. Traced various faults, one of which amazed me somewhat, somebody had fitted a NPN transistor (2SC640) in place of a high-voltage PNP one (2SA1124) in the power regulator circuit. But it still worked, strangely enough. Not having a 2SA1124 transistor I used the closest thing I had, a NTE159. Same problem, the amp stayed on for a while and then randomly went into protection mode.



View attachment 3103

It played absolutely perfectly for about a week, then kept cutting out and going into protection. Traced various faults, one of which amazed me somewhat, somebody had fitted a NPN transistor (2SC640) in place of a high-voltage PNP one (2SA1124) in the power regulator circuit. But it still worked, strangely enough. Not having a 2SA1124 transistor I used the closest thing I had, a NTE159. Same problem, the amp stayed on for a while and then randomly went into protection mode.

View attachment 3104

Q312 was fitted, different lead lay-out hence heat shrink on legs to prevent short-circuits.

Tracing the speaker-protection circuitry - and here I was very ably assisted by my partner at work, who is an electronics fundi (I grew up on valves, not pieces of sand) - we came to the conclusion that the TA7137P IC had an internal fault where the final stage had an intermittent open-collector status and its output was going high intermittently, thus enabling the speaker-protection relay. Proof of the pudding was the fact that there was nothing triggering it to do so as those voltages were spot-on. By earthing the IC's output, I could bring it out of protection. But now I had no speaker protection!

View attachment 3105

The IC (Q551) is obscured under the two blue & one orange wires bottom left of the pic (of course, whoever said it would be easy!)

Frantic e-bay searching web-searching eventually led me to a local supplier who had just one IC in stock, as well as 2SA1124 trannies, so I am hopeful that by this time next week, the Technics will be its usual chirpy self again!

-F_D

But not any longer! It is singing happily along (and has been for the past seven hours) since I replaced that gaga TA7137P speaker-protection IC. While I was at it, I replaced the temporary NTE159 transistor with the correct 2SA1124 which I also managed to get locally. The biasing was still perfect, so I guess I could just as well have left the NTE159 in, but I've got them now.



Sorry guys, still a keeper!

-F_D

 

[Family_Dog]

Me, Mar 16th, 2015:
Sadly, the replacement TA7317P is not an exact match for the original Panasonic SVITA7317P IC, and the amp has run into protection again. There is no fault on the amp other than the voltages on the replacement TA7317P pins are now way out, they make no sense at all. Substituting this with the IC originally fitted to the amp produces the correct voltages and the amp plays once more, albeit intermittently. I have not been able to source this IC anywhere as it is now considered as obsolete. Shorting the output of this speaker protection IC (pin 6) to earth prevents the speaker protection relay from operating and thereafter the amplifier plays perfectly all day long, no DC evident on the output terminals. But while this produces glorious sound, it is not an ideal situation should a fault ever arise as then the speakers will have no protection at all.

So: If anyone has either of the following ICs hanging around, you will be my mate for life:

Panasonic originals: SVITA7317P, or suggested alternative YWTA7317P, also by Panasonic.

The generic TA7317P is not suggested as a direct replacement for this IC, although the functions appear similar. There obviously is a difference in the original Panasonic product although their block diagrams look similar.



-F-D (Frustrated Dog)

 

[Family_Dog]

Me, Mar 29, 2015:

I became a bit disillusioned with the SE-A5 because nothing made sense, whenever I tested it on the bench, everything just seemed right.

And then a little gut feeling hinted to me to hook up the 'scope to the speaker protection IC 'trigger' pins, so I did just that. Lo & behold, all was revealed - there was a very noisy 50Hz half-wave floating on Pin 1 of the IC, which is the pin used to measure for DC on the Speaker terminals. Now this varied in voltage and when it hit positive peaks, it was just enough to trigger the IC into protection. This "AC ripple" is not evident when measuring DC with a DMM, which is what I had been doing up to then. The diode is used to provide a negative bias of -0.9v to pin 1 of the IC, any voltage approaching 0v and above will trigger the IC into protection.

Unfortunately I never took any photos of this because at that stage I figured it would not prove anything.

Now, high ripple in a rectified circuit is usually due to a reservoir cap being duff, so out with the 50uF 3.3v cap and in with a new 50uF 50v (all that I had, but same physical size) and I felt confident my troubles were over.

They weren't, a few minutes later the amplifier went into protection once more.

Disgusted, I left it for a couple of weeks partly because of the damn 'flu I picked up and also because I just didn't feel like taxing an already worn-out brain.

The 'flu passed and I wondered - not for the first time - whether the little rectifying diode wasn't faulty. But I figured it is such a low voltage (12v AC) and so lightly taxed with only milliamps flowing through it, that it could not possibly be faulty. A diode normally works or it does not, I have never come across one that works intermittently.

Until now! I replaced the diode with a 1N4007 (again, all I had) and switched the amp on again, expecting the protection lamp to once more burn brightly. Well... this was yesterday lunch time and up to now, Sunday afternoon, the amp has not yet gone back into protection. A quick couple of checks with the 'scope showed a near perfect DC waveform without AC ripple.

The guilty parties here are D551 and C552 in the circuit below.



Now the number of times I thought about putting a 'scope probe to the pins of the IC and then pooh-poohed the idea as insane, the number of times I bumped the amp against the 'scope base as I turned the amp over (the 'scope is mounted on a smaller shelf above the work bench in the previous pics), and the number of times I had to move the scope probe leads which kept getting in my way as well, were all trying to tell me something: Use the Oscilloscope!!

Touch wood, it seems that the cause of the intermittent tripping of the SE-A5 was one ridiculous 5c diode! Changing the electrolytic cap is also a good idea because the original cap would obviously have had AC applied across it during the times when the diode went leaky.

This is the type of repair that should only have cost less than 50c for components and 30 minutes labour - had one known! I tried to eliminate all the usual suspects and could never find a specific fault, although when I replaced the original TA7317P with newly-purchased ones, all the readings went completely haywire. It seems that those ICs were incorrectly marked and were actually other ICs but definitely not the same as original TA7317P types.



So far so good, the Technics is happily once again coupled to the Marantz tuner/pre-amp combo and Wharfedales and is once more making very sweet music!




-F_D

 

[Family_Dog]

Me, Jun 16th, 2015:

And the Technics SE-A5 did it yet again! Protection light came on - speakers dead. But once again intermittently.

Got a bit disgusted at this stage, so simply yanked the SE-A5 out of service and listened to LM Radio using a Denon 3805 powering the MA Silver 6 speakers for the past week or so.

Today being a holiday, I figured let's give it a go. First thing to do (of course!) was to measure and scope the ripple on D551, which powers pin 1 of the speaker protection relay to a negative voltage. Once again, the diode checked out fine and appeared to be doing its job, but pin 1 had a small positive reading of just about 500mv, enough top trigger the IC into protection. It should have read 0.9v negative. But once more, no fault found anywhere else in the amp, so I removed the diode, 1N4007, that I had previously inserted. Tested the diode again - it was 100%.

So now attention turns to the original diode - a Panasonic MA162A, the original of which is - of course - obsolete. But looking at the specs on a 1N4148 switching diode, the two appear to be a good match. I have 1N4148 diodes in stock, so inserted one.

That was three hours ago and the Technics is still a-singing! Now, what can a simple 1N4148 do that a far beefier 1N4007 cannot do, all it does is rectify a very low 11.8v AC at 50Hz, at a current minute enough to probably not even be measured. Perhaps that was its downfall, it might have been too beefy for the job and was incapable of performing at probably a few microamps? Don't know, but let's hold thumbs now for the 1N4148.

As nice as the Denon is, I feel the SE-A5 matches the Monitor Audio speakers better! I was starting to miss that bright and breezy sound.

And so ends another chapter in the saga, let's see for how long

-F_D

 

[Family_Dog]

This substitution of a 1N4148 diode in place of D551 seems to have cured the problem - finally! Some seven years later and all is still good, I'm happy to say.


-F_D

 

[Family_Dog]

Me, Jun 20th, 2015:

OK, the Technics is still playing and all still seems good!

I have added a 10k resistor across C552 in the circuit above, so that there is a small current drain through the diode at all times. Perhaps it became a bit shaky after the initial charging current of the cap passed through it and I'm surmising it would appreciate a small, but steady, current flow through it to keep it 'switched on'.

Time will tell, at the moment it is once more producing that lovely sound that I have grown to love!


-F_D

 

[Family_Dog]

Me, Jun 20th, 2015:

So AVF member Reef came to visit today, and I conned him into lifting the uber-heavy Sansui AU-111 from the lounge and carry it to the workshop for a once-over. This Amp was connected to the equally heavy 15" Tanny Monitor Gold speakers and should have produced gloriously blazing pure valve sound at about 40w - only it sounded more like 2w at full volume - both channels. This puzzled me because I had not had any volume problems with it before and the fact that both channels were affected seemed to indicate a power supply problem.



I opened the Sansui up and gawked at about 8 years of dust build-up. Connected the amp to my trusty 30w Sony satellite testing speakers and confirmed the volume was very low on all inputs. Inverting the AU-111 into an upside down position so I could measure HT and bias settings on the output valves - all was correct to within 2%, allowing for possible 240v AC mains variances from the mean.

At this point despair sets in. Was I doomed to rebuild this amplifier ala Johan Potgieter style? I was not looking forward to that and immediately wondered how busy Johan was. I ambled back to the PC & printer so I could print out a copy of the schematic for further digging - always useful when you are probing around 500v DC.

But all voltages checked normal, the valves were still 100% as tested on the AVO Mk 4, all the front panel controls were in excellent health and not sticky.

And that was about the time that I looked more closely to the hum-bucking pot on the rear of the channel which was mounted on the rear panel just out of site in the pic, above the 4 x KT88 output valves. This is commonly used to balance out any potential hum caused by small imbalances in the 6.3v AC heater wiring and I was somewhat astounded that they could use such a tiny dual-ganged pot instead of a beefier wire-wound pot for this. So I carefully adjusted this pot and.................. the audio level increased by some few hundred percent. Sansui had fitted an over-all sub-level audio control and if I had only had the rear of the unit facing me and not the front panel, I guess I would have noticed the pertinent wording that Sansui had so thoughtfully provided for people who lack suitable intelligence - "Sub Volume Level Adjust".

Anyway, all was not lost. I reset this to 90% and grabbed a cell-phone pic of the innards. Please do not compare this to Johan's restoration of the AU-111, but it still looks sexy!



Reef, you may come visit me again - I need to cart the monster back to the lounge.


-F_D

 

[Family_Dog]

me, Jan 19, 2016

So the "new" TA-N77ES with new meter lamps fitted...



This is playing over the Tannoy Monitor Golds in enclosures built by Perfectionist a couple of years ago and coupled to the long-last ST-S222ES tuner and a TA-E2000ESD processing unit. Graphic equaliser not indicating anything because I am running it in flat Stereo mode.

The TA-N77ES amplifier uses 6 x 12v globes in series for the meter display. These were last selling at $17 each from Sony - and they did not last long at all. I find it much more economical to get hold of a rope light - the kind used for Christmas trees - and strip the rope lights for the 12v 100mA globes, exactly what the Sony uses. As I got these from a friend at work, they cost me a total of.... nothing! Don't know how long they will last but I do have a plan B in place if they do not last.

So Chingy, what's next?


-F_D

 

[Family_Dog]

Me, Nov 28th, 2016:

Reading kubusi's thread on the restoration (link removed - no longer works on the other forum) of his Mullard 5-10, I realised I had not yet posted pics of mine in this thread. For what it's worth, it is a rebuild of a nearly 50-year-old amplifier and I still have to build its mate. Once again it was totally stripped down and the chassis was powder-coated. The transformers are Partridge.

Here is the finished product undergoing some workbench testing:






It originally had a 8+8uF dual electrolytic cap as the DC filter caps but I replaced this with a modern 50+50uF cap, as evident in the pic.


-F_D

 

[Family_Dog]

Me, Jun 30th, 2017:

Just testing Postimage since Photobucket went belly-up...



Pic is of a Trio 106 FM tuner, valves, that I bought with my Army pay back when the Government of the time decided the country would collapse unless I did my military service after leaving school. Notice the FM tuning range, which is common in Japan.


-F_D

 

[Family_Dog]

Me, July 1st, 2017:

Interestingly, I note that the US versions of this tuner cover the FM band from 80 - 108MHz, not 76MHz as my two units do.The unit above was bought new in 1963 from Wild & Marr and is original in all aspects, same valves. The tuner is standing on top of an upright piano which we were moving from one side of the lounge to the other and it took a tumble on to the parquet flooring A tiny dent in the blue metal cover which I managed to straighten, one valve popped out of its base (still worked when I plugged it back) and both 6.3v dial lights dropped their filaments. I replaced those.

Internals photo below courtesy of Radio Museum.org




-F_D

 

[Family_Dog]

Fredeb, Jul 4th, 2017:

Blikskottel ! They knew how to build them back in the day F_D .

 

[Family_Dog]

Me, Jul 4th, 2017:

Yep! All the above nowadays fits onto a single chip - where's the fun in that? I have two of these Pilots, one for parts and the other to be restored and then returned to its original solid mahogany radiogram cabinet, part of which the 'before & after' 5-20s are resting on in the second pic.






-F_D

 

[Family_Dog]

fredeb Jul 4th, 2017:

Wow F_D - the Pilot is sure gonna look good !

Do they sound good too , when restored ? What drivers will they drive ?

--

Me, Jul 5th, 2017:

The Pilot is a valve MW/SW radio, mono only. It originally drove an 8" PM speaker. Have no idea what happened to the speaker - I don't recall removing it from the cabinet - but will look for something suitable. Nothing modern, I need original sound. So if anyone has an old 8" PM speaker in working condition, I could be interested

I also need to find a suitable output transformer, driven from a single 6V6 valve to about 4 ohms as well as a "magic eye", 6-pin base.

-F_D

 

[marcochezzi]

I enjoyed the read on your SU-V5 amp, thank you for the entertainment..

Regarding the faulty diode (bridge), when I was working in the audio repair workshop at then National Panasonic as a young lad in the latter half of the 80's, I was handed a SL1200 turntable that would not maintain speed.. Would intermittently speed up for a microsecond and then settle back down again in perfect sync for hours on end.. Frustrating as all hell, where does one even start.... I can safely say that I spent many more unbillbale hours on that machine than my manager would have wanted, however the fault was in fact a faulty bridge rectifier diode, that would 'leak' intermittently causing a microburst of DC issues, then return to stability for a few more hours.. While the diode was clearly defective, I often wonder if mains voltage fluctuation could have been the reason for the fault rearing its ugly head every so often..??

 

[Family_Dog]

Thank you for this tip Marco, I have a SL1200 TT that has not yet shown any weird symptoms, but I am going file this for possible future use.

Yes indeed, diodes seem to have a mind of their own. I more or less expect this from Germanium trannies & diodes but not really silicon, but still, it happens!


-F_D

 

[Family_Dog]

Me, July 5th, 2017:

I used the Adcom GP-1 Preamp (pictured above under the Pilot radio) with the Steinhart Amp which is also just sitting now - I need to put both units in action again. Removed them when busy with house alterations. The Adcom has an issue with iffy RCA sockets that I really should replace and scratchy volume control, nothing insurmountable.



Please ignore the dust on the amp, the camera sees things that the eyes do not

Apologies if I start repeating pics but since Photobucket performed its nasty deeds there is no guarantee how much longer the pics already posted will remain visible.


-F_D

 

[Family_Dog]

Fredeb, July 5th, 2017:
That Steinhart TVP-800 is absolutely beautiful , I have a TVP-50E that looks like an air-conditioner

It is interesting , the way he shielded the different sections from each other with those U-extrusions . I guess the circuit of the TVP-800 is similar to the TVP-50 , swopping PL519's for KT88's ?

The PL519's are getting scarce and pricey too now-a-days .

Are those two massive C-cores behind each pair of KT88's ?

Me, July 5th, 2017:
His circuits are all much of a muchness, so I am sure with one or two minor changes it would be the very same circuit.

The transformers are potted, so have no idea what type they are. I personally feel this is one of the more successful amplifiers Gunther had designed and it is a good-looker too.

Fredeb, July 5th, 2017:

.... and it is a good-looker too.

That it is ....

 

[Family_Dog]

@Andre Vermeulen July 10th, 2017:
Those marvellous outputs in the 5-20's.....I have one and I search forever for another....

Me, July 11th, 2017:
Kent, they do pop up for sale now and then. I built one for use as a PA system for a local brick company many, many, many years ago. They are no longer using it but no-one knows what happened to it and my efforts to locate it have been fruitless. It looked the same as the others in my collection and it could have made its way to you with pleasure had I located it.