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Monday, August 7, 2017

Beogram 4004 Type 5526: Finalizing Mechanical Adjustments

As usual with these Beogram 400x turntables it takes a good number of iterations on the mechanical adjustments before I am satisfied that the turntable is correctly aligned and ready to play records again.

The remaining final adjustments on this Beogram 4004 were the platter height adjustment, tracking force calibration, stylus tracking path check, stylus set down limit and the tangential tracking sensitivity.

For the height adjustment of 23mm between the Beogram platter deck and the top of the fixed arm I ran into a problem where the tangential arm assembly wasn't level enough with the floating chassis frame.

I stripped the Beogram chassis down again and moved the set screws for tangential arm assembly height so they could be adjusted from the top instead of underneath the floating chassis. This will save time in the future and not require taking everything apart again if that adjustment needs to be tweaked.

I ran into a second problem which was with one of the set screws on this Beogram. Someone previously had damaged one of the set screws where it could not be removed. I had to use a Dremel tool to drill it out, then re-tapped the hole for a replacement set screw from my spare Beogram 4004 unit.

Once I was passed that issue it was pretty straight forward to adjust the tangential arm assembly, using the set screws, to get the fixed arm level with the chassis.

I re-installed the floating chassis in the Beogram case and adjusted the platter so the top of the platter is 23mm from the top of the fixed arm. Sorry for no pictures but here is a link to some reference pictures from a previous project.

With the deck height set I went about calibrating the tracking force for the cartridge. The way I like to do that is to set the tracking force wheel to 1 gram, then adjust the counter weight and tracking force wheel as necessary so I measure 1 gram with my digital cartridge scale.

Since I haven't put the Beogram deck completely back together I needed a good base for the scale to rest on in order to measure the tracking force. The ridges on the Beogram 4004 platter don't allow room to put the scale under the tonearm so I borrowed a platter from a Beogram 8002 turntable which is completely flat.

I also left the Beogram 8002 platter in place for the stylus tracking path check.

For the stylus lowering limit adjustment though I switched the platter back to the Beogram 4004 platter as the adjustment is to make sure the stylus lowering limit clears the first ridge of the platter.

That is to protect the stylus if the Beogram ever fails to detect that a record is not present.

Everything is looking good so far. The final adjustment I make is the tangential tracking sensitivity. With the platter belt disconnected from the platter motor I can manually rotate the platter. The adjustment is to set the tonearm down on a record track, then adjust the tracking detector so the tangential arm drive motor begins rotating after a couple of (manual) platter rotations. After that the tangential arm motor should move the arm a little bit on every rotation. Obviously the exact results of this check can vary some depending on the record you use for the test. The Beogram service manual calls for a specific B&O test record (3621001) and track (5) that I have never been able to find. So I typically use a couple of old records I have and test the tracking sensitivity on several tracks.

Once the tracking is set I test play the old record and watch the tangential tracking system do its work.

Next step is to connect this Beogram to my listening room amplifier for the first record play test.

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