Restoration of HMV STEREO 666 (1976)

[reubensm]

My god!!!!!! Its near 2.5 lakhs in indian currency. Moreover, no service center in india. But its a Class A product anyway

Yes, the new SL1200 is (according to Technics designers and engineers) not like the original SL1200s. This one is manufactured closer to the legendary SP 10 Mk2. Only the dust cover is made with the same tooling of the last produced SL1200. The SP10 Mk2 is perhaps the greatest direct drive turntable of all time. However as it was a broadcast turntable, it was beyond the reach of many. Hence the SL1200 became the urban legend

 

[anirban420]

Yes, the new SL1200 is (according to Technics designers and engineers) not like the original SL1200s. This one is manufactured closer to the legendary SP 10 Mk2. Only the dust cover is made with the same tooling of the last produced SL1200. The SP10 Mk2 is perhaps the greatest direct drive turntable of all time. However as it was a broadcast turntable, it was beyond the reach of many. Hence the SL1200 became the urban legend

I fear that at this price tag it will not able to catch the market properly....

BDW, can you arrange me a pair of AD161/160?

 

[neelay2709]

Amazing and fantastic thread. Couldn't understand even a single bit of the technical jargon belted out. But i read through the whole thread. I saw the youtube video also. Don't think Manna Dey songs can be heard in digital format. That sweetness will never be there. Congrats on a job well done.

 

[reubensm]

I fear that at this price tag it will not able to catch the market properly....

BDW, can you arrange me a pair of AD161/160?

Yes, at that price range, one could probably look at stuff on a higher plane.

For the AD161/162 pair, you have to keep looking on ebay. They appear every now and then. Most germanium transistors are available. I have even purchased transistors as old as OC71, for an old radio job a while ago. Only thing is that there is postage involved. I had purchased the AD161/162 pairs with some other components hence the shipping costs were off-set. Including shipping the effective cost was around $5. I think the actual cost of the transistors was about $2 for each pair.

The amp project which we worked on was for an old man who was in the merchant navy back in the day and had heard this Philips amp during his European travels back then but for some reason, could not own one. We did a clone just to make him feel happy. Believe me, as simple that circuit is, it sounds really good but one would need to have high-efficiency speakers paired with it.

 

[aks07]

.. 'SL 1200'? Just WOW. Its the best tt ever

Going by the prevailing wisdom some of my other TTs would score higher on that "WOW" factor though I am personally more sober about that. I think the SL1200 is an unmatched act at its segment. But, and again based purely on my experience, its smaller brother the auto return SL Q2 is a more practical package for my everyday use. It is almost as nice as the SL1200 and Im hard pressed to spot any sonic difference with my half century old ears. The Technics duo are certainly a quieter lot. The Garrards too have zero rumble but the idler mechanism adds a bit of its charming notes.

Looking at your TT and speakers I think they would look nicer if you can get a carpenter to do up the laminate. Or wood veneer since you are doing it for keeps.

Ive no idea why the HMV 666 amp circuit is like this. It resembles the old HMV Fiesta design.

. a pair of AD161/160?

Did you check out Railton at Madan St? Even 5 years ago they had a huge stock of Ge transistors. I bought a whole bunch to fix my Grundig portable. They used to have all obscure stuff and depending upon the mood of the day you could strike gold. Try to speak directly with owner and be 400% nice when you do so. The more obsolete the items the nicer you need to be I have got most of my fancy valves, PIO caps, etc from these guys.

 

[greenhorn]

If the germanium sound is not a priority, perhaps the circuit can be redesigned for silicon transistors?
Redesign Germanium Transistor Circuits, Part 1

 

[anirban420]

For the AD161/162 pair, you have to keep looking on ebay. They appear every now and then. Most germanium transistors are available. I have even purchased transistors as old as OC71, for an old radio job a while ago. Only thing is that there is postage involved. I had purchased the AD161/162 pairs with some other components hence the shipping costs were off-set. Including shipping the effective cost was around $5. I think the actual cost of the transistors was about $2 for each pair.

Hi reubensm, can you arrange me ONE AD161? It is not available in ebay.in. I do not have International Credit/Debit card. So I can not pay in any site other than Indian ones. It will be a kind help if you can arrange it for me. This will make my Philips player alive again.

P.S. - I have searched this in Railton Electronics, they do not have this transistor.....

 

[anirban420]

Looking at your TT and speakers I think they would look nicer if you can get a carpenter to do up the laminate. Or wood veneer since you are doing it for keeps.

My dad forbid me to do any carpentry work on this machine. After all it is his machine, I should obey him....

 

[anirban420]

Is there any explanation of the placement of Volume pot before pre-amp? And why the output characteristic changes when it is placed between pre-amp and amp?

Finally I got the explanation of placing the Volume pot before pre-amp. Actually this is done to minimize the click and pop of vinyl. Conventional Log Volume Pot attenuate some High Frequency, and clicks and pops are basically high frequency sound. If we place the Volume pot after pre-amp, then pre-amp will amplify the whole spectrum of sound that will put unnecessary high frequency sound including clicks and pops in the amplified output and it will create further distortion...

 

[anirban420]

If the germanium sound is not a priority, perhaps the circuit can be redesigned for silicon transistors?
Redesign Germanium Transistor Circuits, Part 1

Yes Germaniums can be replaced by Silicons, but probably not by the method shown in the link you have given below, I think the methods shown in the link are theoretically incorrect. First of all, every practical amplifier we use is basically a collection of small amplifiers connected in series, You can get the idea of this if you see the circuit diagram of this machine which was uploaded few post before. To replace germaniums with silicons you have to consider three points - 1) overall gain, 2) Q-point Biasing and 3)impedance matching between every amplifying stage. If we want to replace the final Out-Put Stage (OPS) of the amplifier, its gain can the calculated from the values of biasing resistor and the beta gain (hfe) of the transistor. Now the replacement silicon transistor can biased in the similar gain if the replacement transistor have similar hfe, in this case the values of the biasing resistors can be calculated, next job is to ensure the biasing so that the transistor remain in their "always on" condition (Q-point) and the impedance of the input of the OPS be exactly the same as the output impedance of the output of the previous Driver Stage, impedance mismatch will make thermal runway either of the OPS or Driver stage transistor. All this 'Gain establishment', 'Q-point Biasing' and 'Impedance Matching' needs rigorous mathematical calculations that depends on the transistor of choice and amplification level needed. These are not so easy job.........

 

[anirban420]

Hi Folks,

How are you all. After a long gap, I am back with the remaining part of the restoration job.

My next job is to restore the Level Monitoring Circuit.

At first have a look in the Schematic Diagram of the circuit.

Its unusual because it needs AC input at VCC. Rectification is integrated in the circuit.

Basically the circuit is made up by cascading two Class-A amplifier. Polarity of all transistors and orientation of diodes in power section (D3, D4) in the one channel of the amplifier is just opposite to the other channel.

The first amplifier is made up of AC127 or AC128 (Q2 and Q1) which are acting as Voltage Amplifier here. This stage actually amplifies the transient responses of the incoming signal (Point 1 and 3 of SPEAKER_IN). The next stage is designed with BC158A or BC148A (Q4 and Q3). This stage is Unity Gain Current Amplifier. AC127 or AC128 produce 3V in its output, but the current is low, about 700-800 mA current is needed to en-light a bulb in its full glow. This massive current is produced by the BC148A/158A, but the output voltage is kept same as the input voltage in this stage.

The outputs of speaker is served as inputs of this circuit. And these inputs are connected in an unusual way. one input is connected both to the base of AC128/127 and the other input is connected both to the emitter of these transistors. Basically this is a very cleaver design. Careful placement of R3, R4, R5, C1, C2 ensures that both transistor operates in Class-A mode, these resistors and capacitors are shared by both of these transistors, but the cleaver design keeps the two channel separate. The fact can be visualized by simulating the circuit in any circuit simulator.....

Presence of AC (from speaker output of the amplifier) in point 3 of SPEAKER_IN port enlights LMP1 and presence of AC in point 1 enlights LMP2....

 

[anirban420]

Here is a picture of the board. The diodes (the left-most two and the right-most two) used here are very strange looking. These diodes are in TO-1 package. This type of package is used generally by transistors. I have never seen any diodes using this package....

I was very confused about the value of the Q1 and Q2 transistors. The marking of Q1 was gone, and marking of Q2 was very fed. rigorous editing of the close-up picture of Q2 revealed its marking.

Here is a close picture of diode. The picture was taken during the testing of the circuit. The diodes have very faint markings on it.

Specifications of the diode are as follows -

Diode Name = OR23
Forward Bias Voltage (Vf) @1mA = 168 mV
Forward Resistance = 900 Kilo-ohm
Maximum Current Handled (I-max) = 1A

The value of Vf is a very strange figure. Such a low value!!!!!!!!!!!!!! A good Schottky Diode have Vf at about 215 mV. Dont know by what the diode is made up of, whether it is a Schottky or a germanium diode. Another strange phenomenon I noticed that Reverse resistance of the diode is as same as the forward resistance, whereas reverse resistance should be 100 or 1000 times greater than forward resistance of a healthy diode. My question is, Based on the above-mentioned specifications, is there any Schottky replacement available?

 

[anirban420]

During component testing of the circuit, I found several faults.

1) There is BC548B in the position of Q4. Its a wrong one. BC548B is NPN Transistor. A PNP is to be used here. So I replaced this with BC558B. (Please note that BC548B or BC558B are similar to BC148A or BC158A, 'B' have high gain than 'A', BC'1'48 is lockfit package, where BC'5'48 is TO-92 package, rest of all are same).

2) AC128 found faulty during hfe testing.

3) Light Bulbs were missing.

4) Diodes behave strangely.

 

[anirban420]

Did you check out Railton at Madan St? Even 5 years ago they had a huge stock of Ge transistors. I bought a whole bunch to fix my Grundig portable. They used to have all obscure stuff and depending upon the mood of the day you could strike gold. Try to speak directly with owner and be 400% nice when you do so. The more obsolete the items the nicer you need to be I have got most of my fancy valves, PIO caps, etc from these guys.

It is a very frustrating situation if you find a Germanium in faulty condition. But as per the suggestion of ask07, I tried Railton Electronics. I called Mr. Vineet Ladha of Railton ..................................... AND YES,,,,,,,, THEY HAVE AC128 IN THEIR STOCK....... :yahoo: :yahoo: :yahoo: :yahoo:

I will visit their shop very soon... till then comments are welcome.....

 

[souravin]

This is an excellent thread, very informative and unfolding Anirban's journey towards final goal. Terrific step by step description. Understand how painstaking each step would be. As I use a Philips 533 player for playing 78 rpm, this is pure bliss on the vocals and mids.

I am staying at Dhakuria Kolkata and interested to touch base. Please let me know.

Thanks,
Sourav

 

[anirban420]

This is an excellent thread, very informative and unfolding Anirban's journey towards final goal. Terrific step by step description. Understand how painstaking each step would be. As I use a Philips 533 player for playing 78 rpm, this is pure bliss on the vocals and mids.

I am staying at Dhakuria Kolkata and interested to touch base. Please let me know.

Thanks,
Sourav

Thanks for appreciating my effort Sourav and a warm welcome to my thread. I have sent you my contact number, please check your message box. It will be very nice to meet a vinyl lover from my locality. BDW, I stay nearby to your location...

I am interested to see your Technics TT if you still possess that. And I wonder why do you still prefer old school Philips 533 for 78's? I have no detailed experience with sophisticated TT till date. Do these old TT sounds exceptional over the modern TT for playing some specific types of music?

 

[anirban420]

At first have a look in the Schematic Diagram of the circuit.

There was a careless mistake in the previous schematic. Here is the corrected schematic of the Level Monitoring Light Board Circuit of HMV STEREO 666 ........

 

[souravin]

Thanks for appreciating my effort Sourav and a warm welcome to my thread. I have sent you my contact number, please check your message box. It will be very nice to meet a vinyl lover from my locality. BDW, I stay nearby to your location...

I am interested to see your Technics TT if you still possess that. And I wonder why do you still prefer old school Philips 533 for 78's? I have no detailed experience with sophisticated TT till date. Do these old TT sounds exceptional over the modern TT for playing some specific types of music?

Thanks Anirban. Anyway I don't want to pick away the flavour of this thread. Let's discuss offline.

 

[aks07]

....But as per the suggestion of ask07, I tried Railton Electronics. I called Mr. Vineet Ladha of Railton.....

Do make it possible to meet the owners. On a good day you may even get treated by a special Sindhi chai.

 

[reubensm]

Thanks for appreciating my effort Sourav and a warm welcome to my thread. I have sent you my contact number, please check your message box. It will be very nice to meet a vinyl lover from my locality. BDW, I stay nearby to your location...

I am interested to see your Technics TT if you still possess that. And I wonder why do you still prefer old school Philips 533 for 78's? I have no detailed experience with sophisticated TT till date. Do these old TT sounds exceptional over the modern TT for playing some specific types of music?

TTs of different types and price-points will sound different as with TTs, there are many variables. However a lot of it depends on how one would perceive these differences. Was watching the video of our 666 playing and it sounded so sweet to my ears. I have been through them all, from low end plastic stuff to the top of the line and I have been able to enjoy my music every time I've played a record. I am onto Garrard for sentimental reasons but the best TTs I've owned or listened to are definitely from the Technics DD stable.