Restoration of HMV STEREO 666 (1976)

[anirban420]

What a wonderful site and a great ending.

Also not a bad idea to replace the bolt and nut on the headshell (which you would use as the Finger grip/Handle for the headshell), with something light weight and more appealing to the eye

The Nut/Bolts that are attached to the headshell for attaching the cart and as a handle are the original ones. I think their weights are so calculated that these would apply the correct tracking weight to the groove of record when played with OEM cartridge. Since I am using a (near)-OEM cart, I fear to change those....

 

[anirban420]

What a wonderful site and a great ending.

Not a bad idea to get some work done on the woodwork. With the restoration job which you have achieved internally, this would complete the project and get the TT back to a time when it was in the show-room.

I would second reubensm that you need to put your excellent skills on restoring the wood work.

Let me think what can I do for the wood work. I don't have any knowledge in carpentry. So, If I have to do some work with the wood I have to visit any carpentry shop. For that I have to detach all circuitry, transformer and wiring. Actually these things have to be done at the initial step, before restoring the electronics, or in the parallel to the electronics restoration work. I was not sure about my success, so I omitted that step.

The cabinet is not made up of real wood, its plywood. Every part of plywood is glued actually. During restoration, already a part fell off, I glued that afterword. The outside part which looks like a 'Wood Polish' is actually a cheap quality 'Sunmica'. Its just like a 'polish-looking' paper coating that are used in the outside of box cabinet now-a-days.

And I had not thought about the wood work restoration. Your comment made me to start thinking about it. I was only concerned about to play record in this machine in its near optimum condition, Did not thought or bothered about it's look. Feeling confused to open up everything (which might be a pain), and hand over the cabinet to the carpentry shop (don't know what will go on there during the work) for 2-3 days or a week. what to do? Give me some suggestions......

 

[anirban420]

The way you do things I am confident that this equipment is good for next 50 years. Just stock up on needles and idlers

WOW, will it last for another 50 years? The machine is already 40 years old. My dad overused the machine in his days. The original Ge transistors are still functioning. If it last for another 10-20 years, it will become an antique. I did not changed the value of a single biasing resistor in the power amplifier section, therefore the transistors are still biased in its original state. How long it can last more? I need any expert's suggestion.....

I have two styluses now which are brand new and plays LP on both sides. I am going to buy another stylus having a 78 rpm playing capability at one end. I will buy new or second-hand whatever I will get, if I get a second hand one I will preserve it exclusively to play shellacs. I do not stay in my home, rather go to my sweet home monthly where the player is. I stay there for 1 week. That time only the machine is being played. Whenever I get in touch with the machine I play records regularly. As I can remember, each side of stylus is capable of playing 400 hours of music regardless of shellac or LP. Are my stylus stock enough, what do you people suggest?

Idlers and matched Pulleys are hard to find. Whatever I know these things last long if not tempered. Should I stock an extra lot of those?

 

[anirban420]

Well done!! :yahoo:

Voted a well deserved 5 star.

:signthankspin: reubensm

:signthankspin: aks07

Thanks to the other members who showed interest in my post.

 

[anirban420]

The thread is not over yet. There are few things left.

1. I am going to post a video where I played a record in this machine.

2. I will provide the circuit diagram of this machine with a few detail description of the circuit.

3. The next plan is to restore the 'Level-Monitoring Circuit', I mentioned about this thing at the start of this thread. A few Discussion is needed in that circuit.

4. At the end I will re-post few of the initial pictures in such a format that can be available by non-members of this forum.

5. And probably the wood work restoration story........

 

[anirban420]

Here is the Video of the Player in which I have played a vinyl.

https://www.youtube.com/watch?v=CPfYvpV0flA&feature=youtu.be

 

[anirban420]

Here is the Circuit Diagram of the Amplifier Board.

 

[anirban420]

The circuit has many unusual things. Some of these have been discused earlier like pot mounted Baxandrel network, unusual values of capacitor etc. I am going to discuss another unusual thing in this circuit. Please note the position of the volume control pot, it is connected before the pre-amplifier stage. Generally it is connected between pre-amplifier and amplifier, specially between tone control and amplifier. But this is not done here. Tone control output is coupled to the input of amplifier by a 100n capacitor (C15). Very unusual, is not it? The explanation probably lies in the cartige output level. The cartige gives a near-line level voltage output, which is a common characteristic of ceramic cartridge. Therefore, at the first stage the voltage is controlled by the volume pot, then it is connected to a low gain pre-amplifier. This is my assumption only. I have neither checked the cartridge volatage, nor calculated the pre-amp gain. Any expert comment will be welcomed.

BDW, I used the term 'near-line level' for cartridge output. Its because no moderm amplifier can amplify the output of cartidge directly, a low gain voltage amplification stage is needed for this, I have checked it.

The pre-amp used here is a low gain one, I am quite sure about it. Because any external line level input (AUX, TUNER) is connected to the input of the pre-amp, not to the input of Amplifier stage. The pre-amp circuit type used here is quite common in cassette player pre-amp, the only difference is that those are high gain circuit. Therefore, they are never used for a line level input.

Once i have connected the cartridge directly to the pre-amp and placed volume control in between pre-amp and amp section. The result was increased noise, and change in the frequency response of the amplifier, also gain was changed. There was a high gain distorted output with sharp treble and very low bass. I want an explanation of his behavioral change of the amplifier. Please provide me some.......

 

[reubensm]

Here is the Circuit Diagram of the Amplifier Board.

Quick question, is the ceramic cart connect straight to the input, directly into the 1M pot? Also what setting have you used for the gain pre-set at the emitter of the BC148A in the pre-driver stage of the power amp? The tone control looks like a baxandall passive design.

Did you draw the schematic by tracing the tracks on the PCB or did you have the circuit with you. The old HMVs used to come with either the circuit hardcopy pasted to the inside of the turntable or at times, with the user manual.

 

[anirban420]

Quick question, is the ceramic cart connect straight to the input, directly into the 1M pot? Also what setting have you used for the gain pre-set at the emitter of the BC148A in the pre-driver stage of the power amp? The tone control looks like a baxandall passive design.

Did you draw the schematic by tracing the tracks on the PCB or did you have the circuit with you. The old HMVs used to come with either the circuit hardcopy pasted to the inside of the turntable or at times, with the user manual.

1. Output of cartridge goes to a source selector rotary switch which is not shown here. Output of the switch connects to the input of circuit shown here.

2. Oscilloscope and sine wave generator is needed to set the gain properly. I dont have the both. However, I can use online sine wave generator and oscilloscope app in mobile, but since they are crude technic, I didnot use them. I took the help of my 'audiophile' papa in this case. He used to play any vinyl keeping the tone controls in flat position in his time. He showed me one particular vinyl of our collection which will give satisfactory listening level in home lisyening environment with the Volume dial placed in 10'o clock. This was the key to set the gain. I adjusted the tone controls flat, kept volume at 10'o clock, played that particular vinyl and told my papa to guide me while I adjust the internal gain. This resulted the preset to set in the minimal position, at 7'o clock. Papa told me that some more gain decrease was needed. But it was not possible atm. To achive that, I have to change the preset to a higher value and I wont do that. The reason of this high gain probably lies in the change of BC148A to BC548B. hfe of 'B' is much higher than 'A'.

3. The tone control is not passive. Basically it's a modified Baxandrell. Original Baxandrell circuit was designed in tube. It has a transistorised version also which is biased in Class-A Common-Emittor mode, the tone control network works there as a feedback circuit placed between Collector and Base of the transistor. Here in this circuit, audio signal after C4 is at first proccessed in the Baxandrell Network, then it goes for voltage amplification at Q3, which also sets the gain of the amplifier via it emittor degeneration trim-pot.

4. I drew the circuit by tracing PCB lines. Its drawn in EAGLE and edited in Powerpoint. The machine had the circuit printed in its manual, as told by my papa. But the I never have seen that manual book in my life time, it has long gone......

 

[reubensm]

watched the video, very nice

looks like you have another TT on the rack, just below the drawer?

 

[anirban420]

Yes, its a Philips Hi-Q International. Forgot the model number though. It was bought in used condition few years back.... Its made up of AD 160/161 Ge pair, of which one transistor gone. Its impractical to search for a Ge replacement. I have planned it to sell to Musha Bhai

 

[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?

 

[aks07]

Loved the video. Your voice-over is as sweet as rosogolla ! :clapping:

And a thousand thanks for spinning Maa Maago Maa Aami Elem Tomar Kole. I am probably hearing it again after 40 years. A glorious ode to the Mother.

WOW, will it last for another 50 years? The machine is already 40 years old. My dad overused the machine in his days.

And why not? If it has survived 40 years it has already passed the test of time.

For reference my three Garrard turntables are from 60's. A pair of QUAD amp is from the 50's. My regular everyday Radio is from the 50's. The portable Grundig transistor set is from mid 60's. Its AF section still has the original germanium although the RF section has needed replacements.

Some of my everyday use triodes date back to the 40s. Currently my main amplifier is a SANSUI 771 which was made in 1972. The Nak 600 deck is from early 70's.

My youngest audio equipment is the pair of Technics SL1200 and SL Q2 from late 70s.

But I am not counting the various CD/DVD players as they seem to last only about 3 years max.

Almost all of my older equipment function perfectly. In fact the Technics pair look and perform just as they did when new. They are still in 100% original condition. Never needing any repairs and the maintenance has been the usual 2 drops of Singer oil each year. And they continue to be used extensively but of course handled more carefully nowadays.

The Garrards have been on original Idlers, springs etc. I have just once taken apart the motor and spindle for oiling and replaced some random rubber parts such as the grommets. That is all and they are still perfect although not as noiseless as the Technics.

All these equipment were bought used. But after a clean up and repairs/restoration wherever needed they have become almost new.

So dont worry and use them often. Along with periodic maintenance that is the best insurance policy for these things.

Added later:
Is the polarity of the output DC cap correct?

 

[anirban420]

Loved the video. Your voice-over is as sweet as rosogolla ! :clapping:

And a thousand thanks for spinning Maa Maago Maa Aami Elem Tomar Kole. I am probably hearing it again after 40 years. A glorious ode to the Mother.


And why not? If it has survived 40 years it has already passed the test of time.

For reference my three Garrard turntables are from 60's. A pair of QUAD amp is from the 50's. My regular everyday Radio is from the 50's. The portable Grundig transistor set is from mid 60's. Its AF section still has the original germanium although the RF section has needed replacements.

Some of my everyday use triodes date back to the 40s. Currently my main amplifier is a SANSUI 771 which was made in 1972. The Nak 600 deck is from early 70's.

My youngest audio equipment is the pair of Technics SL1200 and SL Q2 from late 70s.

But I am not counting the various CD/DVD players as they seem to last only about 3 years max.

Almost all of my older equipment function perfectly. In fact the Technics pair look and perform just as they did when new. They are still in 100% original condition. Never needing any repairs and the maintenance has been the usual 2 drops of Singer oil each year. And they continue to be used extensively but of course handled more carefully nowadays.

The Garrards have been on original Idlers, springs etc. I have just once taken apart the motor and spindle for oiling and replaced some random rubber parts such as the grommets. That is all and they are still perfect although not as noiseless as the Technics.

All these equipment were bought used. But after a clean up and repairs/restoration wherever needed they have become almost new.

So dont worry and use them often. Along with periodic maintenance that is the best insurance policy for these things.

Added later:
Is the polarity of the output DC cap correct?

Hehe, thanks buddy for your comment on my rasogolla voice, it made me laugh:lol::lol:, and also thanks for providing such valuable info.

And you have that very 'SL 1200'? Just WOW. Its the best tt ever, however now out of production. Somewhere I read that Technics may bring it back to production line. But just like 'Bajaj Chetak Reproduction Rumor' I don't know whether it will happen or not. Though I have planned to buy a AT LP-120 after completing my PhD this year. It will be a 'Thesis Submission Celebration' for me.

Yes, I have put the output cap in wrong polarity in the schematic by mistake........

But is there any explanation to my question?

 

[reubensm]

Yes, the 1200 is coming back, but with a $4000 price tag

On listening to the sound on your video, when you placed the tonearm on the record, a distinct hum (rumble) can be heard. I suspect your motor player's motor would need some internal service. Also probably the motor dampening can be improved. Also listen to the power transformer of the amplifier carefully, ascertain whether it is humming. If yes, ensure that it is dampened as well. These are purely assumptions based on what I heard.

Recently I was involved with the building of a clone of a vintage Philips amplifier 22RH580 for a dear friend and sourced the AD161/AD162 pairs from ebay for $5 a pair. Here is a pic of the original amp of which, the clone was built.

 

[anirban420]

Yes, the 1200 is coming back, but with a $4000 price tag

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

 

[anirban420]

On listening to the sound on your video, when you placed the tonearm on the record, a distinct hum (rumble) can be heard. I suspect your motor player's motor would need some internal service. Also probably the motor dampening can be improved. Also listen to the power transformer of the amplifier carefully, ascertain whether it is humming. If yes, ensure that it is dampened as well. These are purely assumptions based on what I heard.

Yes, the player has rumble in the motor. Papa said that it was present in new condition too. And this type of rumble was common in budget players in those days. Its heardly audible during music playback.

The motor is spinning without any drag, its shaft is also properly greesed, and its very free to rotate.

The amplifier dont have any kind of hum or hiss. Its a very low noise ampli, I have hardly seen such a low noise floor in budget ampli.

BDW, how is the sound of the player?

 

[anirban420]

Recently I was involved with the building of a clone of a vintage Philips amplifier 22RH580 for a dear friend and sourced the AD161/AD162 pairs from ebay for $5 a pair. Here is a pic of the original amp of which, the clone was built.

Nice amp. Eager to hear the sound of the clone you made. BDW, Can you arrange a pair of those Ge also for me? And a new Philips stylus? I can provide you the photo

 

[reubensm]

Yes, the player has rumble in the motor. Papa said that it was present in new condition too. And this type of rumble was common in budget players in those days. Its heardly audible during music playback.

The motor is spinning without any drag, its shaft is also properly greesed, and its very free to rotate.

The amplifier dont have any kind of hum or hiss. Its a very low noise ampli, I have hardly seen such a low noise floor in budget ampli.

BDW, how is the sound of the player?

Sounds very good. I have heard this turntable play when I was a kid. I distinctly recollect our visits with dad and mom, to the record store. They had the 666 and a 1010 for sampling music. I distinctly remember the level indicator lamps flashing too. Great memories.