Hi:

I need to replace a 25V 25mA light bulb that sits in the base of the Beogram 4002 tone arm. It provides th servo signal to advance the arm.

I've not had much locating replacement bulbs of the right size in the USA. Does anyone have this part?

The alternative is to replace the lamp with a yellow or white led which may or may not work. Anybody try?

Derek

I suspect that you may need the bulb,rather than a led.The lamp light is reflected off the turntable onto a light dependent resistor,so sensitivity might be crucial?Apart from the arm drive system,there is also in place,a system to prevent the arm lowering onto an empty turntable and damaging the pu!

Can Martin (Dillen) from this forum perhaps help with the bulb?

To clarify, the bulb that needs to be replaced is not the bulb in the sensor arm.

The bulb is located in the tone arm carriage below the turntable platter.

RS Components (http//rswww.com)do a 28volt,24mA wire ended bulb,that I imagine would do the job.Part No.587-686.You need to position the lamp critically in order that the servo regulates correctly,ie:the arm should move approx once every turn of the turntable.

Link is www.rswww.com

There has been a rush on tangential parts lately and I have no lamps of the correct type in stock. RS 587-686 is a bit smaller than the original lamp but specs look close enough in my opinion and it may do the job. Do let us know how it works if you decide to try.

Martin

Solderon29, Martin:

Thanks for the link and the tip. The bulb is a bit small, and because B&O drives these things with only 20 volts (to prolong bulb life) the glass envelope may not disperse enough light or it may be more sensitive to positioning. One alternative is to use 2 12V bulbs of this size in series. 

Here was my solution:

I'm using a T5.5 Telephone slide lamp. The original lamp is epoxied into a plastic shell. Using a small flat head screw driver, I dug out the epoxy.  The T5.5 is a large lamp. It is roughly the same diameter but about 2.5X as long. I broke of the end of the metal slideing tab (the epoxy wedge on the lamp) and then soldered wires to it. Then I slipped it back into the plastic shell and screwed the entire assembly back in. The shell sticks out a bit, but works fine.

The more ideal substitute is a T1-3/4 European Wedge. Studer/Revox uses these to illuminate the VUs in B77/PR99 and A80 reel to reel decks. Our European friends will find this very common, but in North America, I've had no luck finding the 24 volt version of this bulb. You will of course need to solder leads on to this one as well.

I know neither of you really need this info but I thought I'd put my thoughts down for the record in case others stumble over this need.

I do think that a bright yellow or white LED is still a viable option but have not tried. I know people have used LEDs successfully to replace the lamps on the end of tape sensor on Studer mastering tape recorders.

Cheers,

Derek

Neat! Necessity being the mother of invention etc.? I remember that the bulb siting was critical,but assume it was because a light dependent resistor was used as sensor.Later,more sensitive led/photo transistor arrangements were used for this type of servo.You can't very often improve on B&O design,but it would be interesting to try a modern optical solution .

Regards,

Nick