Beogram 4000: Restoring the Hood

I finally got my act together and polished the hood of the recently restored Beogram 4000 from Norway. I need to be in the right mood for this 3 hour work out and so I put it up for a few days...it just was more fun to implant a custom designed transformer into a formerly humming Beomaster 4000..;-). 

The hood of this Beogram 4000 showed the usual signs of age and had some deep scratches and other blemishes. Here is an impression of the situation:

So I started out by planarizing the surface with 220 grit sand paper and then polished it back to a translucent state using a Micro-Mesh polishing kit:

After cleaning off all the polishing residue it was time to install new rubber bumpers on the front corners. They level the hood and make closing it a so much more dignified event. The original buyers were long broken off and only their mounting stubs remained embedded in the respective holes in the hood:

I used a 2 mm drill bit to get the stuff out:

and then implanted small segments of 2 mm diameter O-rings:

The 3D printed red square serves as a template for the razorblading of the rubber pieces to the right length on both sides for a level hood:

The final touch was to replace the screw that served as right side hinge with the original metal rod that was sent along with the turntable:

After implanting the rod:

Much nicer! This should be it. I will now play this Beogram 4000 a bit more to make sure that there are no loose ends or intermittent issues and then it will be time to send it back to its owner!

Beomaster 4000 (2406): Installation of Custom Designed Toroid Transformer

This is a follow up to my recent posts about a strongly humming transformer in a Beomaster 4000 (2406). This Beomaster is in great condition otherwise, so it made sense to install a new transformer to get this unit ready for the next 40 years of service. Most modern audio designs with analog power supplies use toroid transformers due to their much better EM characteristics. After characterizing the original transformer current loads in the secondaries, I designed a replacement and had it custom made by the Toroid Corporation in Salisbury, MD. It costs a pretty penny to get this done, but the result is pretty, too (at least from a geeky engineery point of view...;-). 

While the installation of a new transformer is fairly straight forward, the details can be pretty daunting. The first order of business was to remove the old 'rectangular' transformer. Here is an impression of the original state of affairs:

This shows the 'cavity' after removing it:

The challenge here was essentially to fit (and hold securely) a donut into a square space. Furthermore, The Laws of Beolove require to not drill additional holes into any B&O equipment, ever! My technical upgrades are always 'reversible', i.e. the units can be returned into their original state if so desired at a later point in time. So I set out to design a 3D printed mounting bracket that would fit exactly to the mounting holes of the original transformer case.

Since this bracket represents a fairly large part from a 3D printing perspective (the final design took about 26 hrs to print), I began the design process with an initial study that 'put the mounting holes into the right positions in space', but that needed minimal printing effort so the design could be iterated in a  reasonable amount of time (it is difficult to do precise measurements within a crowded enclosure). Here is an impression of one of these study parts implanted into the cavity:

Once the holes were close to the proper positions, I completed the design and created a final version of the bracket that was able to hold the toroid and the main rectifier in place:

This shows the final design after four prints (and about 1.5 kg of plastic filament...;-) that did not fit precisely and had other fit-related issues. It turned out that the 'study' prints were slightly flexible, which allowed me to bend the holes a bit to the right positions, while this final design is very rigid and so there was no more room for mismatch. This shows the toroid and the rectifier added:

Before I was able to install the toroid assembly, I needed to replace the reservoir and speaker capacitors to make a bit more room for the toroid. The original reservoir capacitor is a bit thicker than its modern replacement, and that gave me five more millimeters that were required to fit the toroid:

This shows the installed bracket with rectifier in place and the new capacitors::

Add toroid:

The next step was connecting the toroid to the input voltage selector. This shows the arrangement at the input selector:

The it was time to verify that the connections were made correctly for proper voltage transformation at all four input voltage settings. This was the moment where I would get proof that my transformer design was correct. All this can be a bit confusing since the input selector switches the various primary coils of the transformer in series and parallel depending on the tuns ratio that is needed for a particular input voltage. So I hooked up my 110-to-250V variac to the line plug of the Beomaster (turned 'on') and then slowly ramped up the transformer voltage for each of the input villages while monitoring the secondary voltages. This shows the setup:

The secondaries wires are held securely apart from each other by some carpenter clamps in concert with thick cardboard strips. This shows the measurements for the various input selector settings vs the 50V secondary. 110V input:

130V input:

220V input (and 22V secondary):

and 240V:

After this I put the input switch back into its box together with the fuse holder (secured in place with some double sided tape):

After this I connected the secondary windings to the two rectifiers:

And then it was time for the magic moment! I slowly ramped up the variac and the 'ON' light came on. Then I connected speakers and an antenna, and set it to FM. And everything seems to work! And of course no transformer hum at all! This is Beolove! I still need to procure a nice bolt to hold the toroid in place in its bracket, but I think it is pretty safe to say that this Beomaster 4000 is back in business. I will give it a full recap and then give it some play before sending it back to Italy! 

Beogram 4002 (5513): Infusing Oilite Brass Bearings of DC Motor with Oil Under Vacuum

One of the challenges with restoring DC motor Beogram 4002/4 Types (551x and 552x) is the restoration of the motor itself. Most of the DC motors present themselves with loud running noise and/or strong RPM variations at this point in time. It turns out that simply taking the motor apart and lubricating the brass sleeve bearings with grease is only a temporary solution.

The bearings used in these motors are 'oilite' brass bearings (see a recent thread on Beoworld where Dillen hinted at this). Such bearings are infused with oil after manufacturing. The brass is porous, and therefore oil can be 'inserted' into the metal itself via a vacuum based infusion process. This results in light duty bearings that can run without the need for external lubrication. However, over time the oil is slowly depleted from the bearing metal (and probably distributed inside the motor). Once the oil is gone and the bearing dry the noise issues and RPM variations start occurring.

The restoration of the bearings requires to infuse fresh oil into the metal. Unfortunately, one has to completely disassemble the motor to get to the bearings (one can force them out without disassembly, but it is impossible to get them back in...).

Here are a few impressions of the process. This shows the motor disassembled:

The two bearings are actually different:

The bottom bearing is shown right with its plastic support washer next to it. The top bearing is on the left. It is slightly bigger.

The infusion process can be done with SAE 30 motor oil and one needs to pull a vacuum in order to suck the air out of the pores of the brass volume to make room for the oil that it can diffuse in by means of Brown's motion. I did this with a FoodSaver vacuum sealer unit that came with an attachment for Ball mason jars. Here is an impression of the bearings in the oil under vacuum in the jar:

As soon as the vacuum is applied small air bubbles arise from the bearings. They accumulate on the surface of the oil as seen in the photo. It is interesting to note that the top bearing produced considerably more bubbles than the bottom one. This is probably a result of the higher friction seen by the top bearing due to the belt torque applied to it. After about six hours the bubbling pretty much stops and the bearings are ready for re-installation.

This is where it gets a bit difficult since the top bearing is held in place with a metal ring that is fixed in place with tabs that needed to be bent up to get the bearing out. It can be difficult to get the tabs bent back far enough to ensure a snug fit of the bearing in its fixture.

I designed a 3D printed tool to simplify this process:

The red cylinder goes inside the motor housing to hold the ring in place:

Once the ring is pushed up all the way the tabs can be bend slightly with pliers:

the final press fit of the tabs into the small recesses is then done with the top part of the tool and adjustable pliers against the red bottom part:

This results is a pretty tight fit almost as good as before disassembly:

I am planning to make a video about this process. But for now it is time to test this motor for 24 hrs using my BeoloverRPM device:

33.33! So far so good! Let's see how this motor feels about things tomorrow!

Beogram 4002 (5523): Some Final Touches - Replacing Plinth and Keypad

After installing the BeoloverRIAA internal preamplifier and the Commander remote control, it was time for some final touches for this Beogram 4002 (5523):

Here is an impression of its damaged plinth:

The replacement plinth I recently came across unfortunately also had some small damages. The corners were slightly banged up. Inspired by the veneer repair I recently carried out on a Beomaster 8000, I set out to do the same to this plinth:

This shows the right corner before:

and after I added a bit of veneer and colored it to match:

not perfect, but definitely much better than before. The left corner had a similar issue on the side:

I did a similar job here:

The original keypad had a big hole in the coating of the start key:

I replaced this keypad with a much better one:

Alright! This beolovely Beogram is now ready for the return trip to its owner!

Beogram 4002 (5523): Installation of Beolover RIAA Preamp and 4002 Commander Remote Control

I recently gave a Beogram 4002 (5523) the usual 'functional restoration' treatment, which concluded with the installation of gold plated RCA plugs. My customer subsequently decided on having my just completed internal BeoloverRIAA preamplifier installed along with the 4002 Commander remote control system that allows the control of all functions with a paired Apple remote.

So this is the first 4002 that is outfitted with both the Commander and the RIAA preamp. A truly 'back to the future' Beogram!

This shows the BeoloverRIAA board before installation:

and assembled with the 3D printed support:

and installed onto the output PCB (#8):

On to the 4002 Commander. This shows the board before installation. It plugs directly into the keypad connector on the main PCB:

This shows it installed:

Here is a view of both boards:

Time to celebrate this upgraded 4002!:

I selected "Sam' Suffy" by Marc Moulin. All his 'Placebo' records (1971-74) were recently reissued by Music on Vinyl on appropriately colored vinyl. Perfect for showcasing this ahead of its time Beogram 4002!

Beogram 4000/4002/4004 Relays: Professionally Manufactured PCBs!

I recently redesigned the Beogram 4000/4002/4004 relay adapter boards to be manufacturable by a professional PCB supplier. I started filling orders with the new boards. Today I made a bunch and I thought they look quite Beolovely!

Here is an impression:

They are available for both the old-style Siemens and the newer vintage National relays that are found as RPM and/or signal path grounding relays in the various 400x models. The boards simply drop into the footprints of the original relays. The relay featured on these broads is a modern encapsulated relay made by Omron, a major Japanese manufacturer. They are rated for a minimum performance of mechanical 50,000,000 and 100,000 electrical operations under load (1 Amp). Since the current switched in the Beogram applications is minuscule, they will last probably close to the mechanical performance limit, meaning that they will probably outlast the rest of the turntable by far. 

These blog posts give an impression about their installation in various Beograms:

Beogram 4002 (5521): Replacing the Electrolytic Capacitors, New Relays and New RPM Trimmers

Beogram 4000: Replacement of a Stuck RPM Relay with a Modern Encapsulated SMD Relay

Beogram 4002 (5513): Further Improvement of the RPM Stability Through Replacement of the RPM Trimmers and the RPM Relay

There is also a video about replacing the RPM relay in a Beogram 4000:

Beomaster 8000: Installation of New Keypad Ribbon Cables

I recently received the lower front panel of a Beomaster 8000 for the installation of new keypad ribbon cables. The original ones had developed some bad contacts in the attached headers.

I designed proper replacements and had them custom manufactured:

I extracted the original ribbon cables and installed the new ones:

Then I open up one of my Beomaster 8000s and tested the keypad with the new cables:

Beolovely!! All keys worked as they should and so hopefully this restoration will come to a successful end soon!