R206 MkI Mechanical Refurbishment

 The first task is to get the receiver working. It would not be a good idea to make it look nice if the thing had a dire mechanical fault. The first step was to investigate the controls. Everything was very stiff, the rotary controls and switches, including the main tuning dials and, worst of all, the wavechange switching. The latter would look at home in the engine room of the Queen Mary. I tackled this first.

The main parts are the turret tuner drum, mounted on phosphor bronze bearings, which is driven by a large worm gear coupled to a gearwheel bolted onto the end of the drum. A chain couples this gearwheel via a pair of toothed gears to an indicator dial visible through a plastic window on the front panel. There are four grease nipples so I investigated these first. The starting handle control could barely move the mechanism so maybe something is seized? After removing the grease nipples, I found each had grease in the threaded part but the bearings themselves were dry. Maybe that's the answer, so I filled each of the bearings with oil and tried again. Turning the starting handle was very slightly easier, except most of the movement wasn't the turret rotating, it was the drum moving laterally by bending the end casting sideways (and it's a pretty heavy casting). Maybe the main control shaft is bent? This would perhaps push the drum laterally rather than turning it.

I unscrewed the two bearing tops and, after dropping the chain, I removed the drum. Nothing obviously wrong. The starting handle turned easily enough. I looked at the worm drive. It was packed solid with hardened grease. More like toffee than grease. As the main drive shaft is riveted in place I had to clean the worm gear in-situ. Using a solvent I removed loads of the old grease.

Below: Drum removed from receiver

 The drum bearings are a little worn but perfectly serviceable. I removed almost as much toffee-like grease from the main gearwheel on the drum.

While the drum is off, I'll clean the contacts and check there are no missing screws etc. The drum carries 24 triangular nickel plated copper boxes containg RF coils and all their electrical contacts are rhodium plated.


Worm gear coated with toffee


End bearings, chain and band indicator

Below: Mating gearwheel for the worm gear

Below: Bearing at the other end of the drum

Below: Chassis with drum removed

Below: RF Module showing spring contacts for the drum

The wires are the connections to the 4-gang tuning condenser

 Next, I removed the band indicator. This was stiff to rotate but will be easy to clean and lubricate. The six numbers around the indicator are nearly black rather than white and will need cleaning or re-painting.

 Band indicator with badly discoloured numerals and part-seized mounting


Above-the cleaned up indicator.

Right the drive chain for the indicator which is very awkward to line up so the correct band number is visible in the correct place.



After putting the wavechange parts back in position I noticed a 4BA shim on the bench. Clearly not a washer as it was too thin. I discovered that without the shim beneath the RH drum bearing there was insufficient clearance between the worm drive and its gearwheel resulting in very stiff operation of the drum mechanism. Fitting the shim proved it wasn't quite thick enough so I fitted a slightly thicker shim and all was well. The chief problem then was to orientate the band indicator. One chain link out and the numbers were higher or lower than the window in the front panel. By trial and error I eventually got the orientation right, but only after a dozen attempts. Prior to this I cleaned the inside and outside of the plastic window.

 Thinking ahead, because of the difficulty removing the main wavechange drive shaft, I'll probably just remove all the knobs etc, mask some areas, and paint the front panel in-situ.

I made a new triangular metal cover for the aerial/earth terminals as this was missing. I may fit some terminals from an R107 or alternatively, just fit a PL259 socket. As the panel is detachable there's no reason to make the new one inconvenient to use.

The next job is to free up the tuning mechanism. This is a complicated thing with several gears and a slow motion drive unit.

Removing the two knobs revealed the rear of the larger one (with the vernier) was thick with toffee-like grease. The locking mechanism was fouling the inner circular disk. I removed the locking mechanism and found a couple of spacers were fitted. I guess these are not right. There are four 4BA nuts apparently securing the inner disk but removing these did not permit removal of the disk. After squirting penetrating oil into the gearing the mechanism was freer but appeared to jam at one position so further exploration is necessary....


This toffee-like grease was everywhere


Slow motion drive visible after knobs are removedThe outer disk is for locking the tuning



View after the slow motion drive is removed. This is done by slackening the securing ring behind the front panel using a long screwdriver.

On the left- before removing the vernier dial.

 Below are other parts. The vernier dial, locking mechanism and the cover from the tuning condenser drive gears.

 The next step was to free up the tuning dial. This is a drum carrying the six waveband scales on a cylindrical dial screwed to two circular end plates. The drum is mounted on a quarter inch shaft secured by 4BA screws to a pair of mounting plates. Both plain bearings were seized. The drum is also mounted on another plain bearing a couple of inches in diameter. This was also completely seized. The three bearings are all similar in construction with phosphor bronze rubbing against nickel. Lubrication is supposed to be via a channel running around the inside of each bearing. The three bearings are all dry and this has produced wear transfering the softer metal to the harder surface and eventual seizure. I dismantled everything and used a fine emery cloth to reduce the diameter of the shaft passing through the axis bearings and to polish the phosphor bronze surface of the larger bearing. this freed them up but not completely. The problem I think is the way the dial is secured to the end plates. The dial material has shrunk and because this isn't equal the two end plates are not exactly square. I slackened the dial securing screws to improve matters but it's not ideal.

The receiver I guess had a planned lifetime of the duration of WW2 so you can't blame the designers for events occuring over 70 years later.


 The dial is driven from a shaft coupled to the tuning condenser drive shaft. There's a centre shaft about which the dial turns.


 At the opposite end to the drive gear is a plain bearing which was completely seized.

The cable carries power to the lamp inside the dial.


 The dial is in really good condition apart from shrinkage which has resulted in bowing. The bowing which is slightly unequal has resulted in the end plates being slightly off-parallel hence making the bearings run at a slight angle.. hence stiffness.


 The dial cover. The plastic has shrunk and bowed and pulled away from its rivets in a couple of places.

The paint has deteriorated to the point it can be rubbed off.

On the left is a small door which can be opened to gain access to the bulb which can be drawn out on a shaft.

Underneath is an aperture for illuminating the vernier.


 The inner tuning knob in pieces for cleaning


 The inner tuning knob after cleaning and reassembling. It has considerable weight intending it to act as a flywheel.

 Right is the anti-backlash gear mechanism built into the tuning condenser, again smothered in toffee-like grease.


 Having just about got the dial itself more or less freed up the next step was to look at the tuning condenser drive. The tuning knobs are connected to a slow motion drive connecting to a 7.8mm (or 5/16 inch) output shaft To test for stiffness in the tuning condenser I had to make an adaptor so I could turn the drive shaft. There's a fair bit of resistance to turning. I have an old R206 and that one allows the dial to be spinned rapidly. The new one alas is too stiff for that and in fact is too stiff for the slow motion drive to operate properly. Finding the source of the stiffness was not easy. First the gearing. I squirted lots of WD40 to little avail, maybe only a 10% improvement. When I had the drum removed I remember seeing an adjusting screw which is only accessible with the drum removed, so I had no option but to remove the drum again. Slackening the adjuster nut allows the screw to be tightened or loosened. It seemed OK so I needn't have removed the drum, however I might check the parts inside the tuner unit and it'll be easier to do this with the drum removed.

What's left to sort out? The tuning condenser is a work of art. The four rotors are all isolated from surrounding metalwork and are connected to the tuner by brushes. Each rotor is made up of plates bolted together. Each of the four rotor assemblies is carried on a bakelite tube screwed to the condenser operating shaft. The shaft is connected to the lower bronze gearwheel in the picture above and the upper gearwheel connects to the input shaft carrying a worm drive.

You can just see in the picture above the main drive spindle emerging from the gearbox. This is carried by yet another phosphor bronze and nickel plain bearing, and I reckon this, and the one mounting the lower section, is seized. The bearing caps for the two bearings are secured by tiny screws which look to be inaccessible so I'm taking a break for now....

The next day I'd placed orders for some lift repairs so I had the afternoon to play with the new R206. The tuning condenser didn't seem quite as stiff so the penetrating oil is working. I removed the two end adjusters, one of which could only be removed once the wavechange operating shaft had been moved... four 0 BA screws. I was then able to move the main condenser shaft longitudinally to judge any bearing stiffness. Eventually after a lot of fiddling I decided it was worth calling it a day as the tuning seemed smooth enough, albeit slightly heavy.

 As the slow motion drive was pretty rough I dismantled it. There are numerous parts, none had any lubrication. The picture below shows the parts. It's held together by four 4BA screws with locknuts.

When the four 4BA screws are fully tightened there is some reluctance to produce drive when constrained and, as the slightly stiff tuning condenser and the slightly stiff tuning dial might prevent the slow motion drive working properly, I decided to look into tightening it up. It's basically a ball race using four ball bearings running in a groove in the operating spindle. The ball race is tensioned by an upper and lower cover (centre left and right). The cap at the top right is pulled against the disk, pressing the upper cover against the ball bearings via the spring (top left).

Because the oddly shaped spring has been under tension for 70 years I reckon it must have lost some of its springiness so I added a shim under the cap to provide more pressure on it. Tightening up the four screws showed that this had fixed the problem of slipping. With the four screws fully tightened the drive wouldn't turn. Slackening them gradually produced a nice smooth action without a lot of resistance. The next step was to adjust the four screws to allow the outer disk to rotate square and true. This was done by fixing the drive to an 8mm twist drill bit in a vise and turning the drive, noting which screws needed tightening or slackening by using a fixed pointer almost touching the outer rim of the disk. The task is like adjusting spokes on a bicycle wheel. Eventually the outer rim was able to be rotated without deviating. This rim is normally locked in place when tuning the receiver.

Finally the lock nuts are put in place on the four screws. Strangely, I found that tightening these altered the drive resistance, such is the sensitivity to adjustment. What must be happening is the screws are pulled against their threads, rather than vice versa, and the tiny variation is sufficient to change the friction setting of the drive.

 The next job is to reassemble the tuning gear and dial and, if it's all satisfactory, to detach the front end to check its components.

Then the tuning drum will be refitted.

The picture below shows the dial and the vernier refitted


Below: the tuning knob refitted with a cleaned up locking mechanism in place


 I was finally happy with the mechanical overhaul. There was almost no wear but all the bearings were seized and took a lot of persuading to free up. The next step was to apply power and see what happened.

 Next I'll proceed to the electrical refurbishment

See the R206 Electrical Refurbishment


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