Repairs on a Wurlitzer 300

[Figno]

Hello group,

I'm new here, so far I am impressed with the kindness on this forum. I wished facebook was like this :-)

I am working on a 300 for a local studio. This one makes a lot of noise (hissing and popping) like a leaking capacitor or broken resistor. But so far all the resistors and caps seem fine. When I disconnect the volume pot the noise dissapears. Introducing audio at the volume pot return line results in a clean signal. So the problem is in the pre-amp.
I noticed a faily new transistor at Tr2, a BC169B. I suspect someone has serviced this 300 before and replaced the transistor with something that seemed compatible but is not. So the hunt for the right transistor has started, but: I can't find any info on the 300. No part lists, no schematics. It looks fairly like a 206 schematic but its not exactly the same.

Does any of you have a schematic or partlist? Any ideas which transistors to use? I am tempted to 2n2926 or 2n5089 (as in 200 and 206).

Cheers and keep up the good work.

[pianotuner steveo]

Hissing and popping usually is caused by dust/dirt/solder blobs or other foreign matter laying on the reeds. It also can happen from condensation when moving a Wurlitzer from a cold environment to a warm one.

Inspect and clean the reeds before messing with components. A brush and an air compressor will help, but the compressor can cause temporary condensation as well.
The reed bar is essentially the preamp.

[Figno]

Hello Steveo,

Thank you for your rrply. The reeds were my suspect too but when I disconnect the reedcable the hissing and popping stays. I will do some more measurements soon with my scope to see where the noise is introduced.

[pianotuner steveo]

I thought that you said when you bypassed the reeds and injected a different signal, the audio was clean. I've never actually seen a 300 in person-do they have the little preamp board mounted in the middle of the reed bar like the 200A? If so, check that board for cracked traces, etc.

[Tim Hodges]

It uses a 200 model amp, so no separate pre-amp board.

[DocWurly]

Does a 300 have the same electronics as a 201?  If so, that would increase your potential user database a tad.

[Tim Hodges]

Not the best image but this shows a 300 amp:

http://www.kerschhofer.net/wurlitzer-replacement-amp/original-board.png

Found this comment by Jenzz:

The innards and circuit are the same as the EP201, a EU-Version of the original 200. The amp is close to the 200 schematic, but has some additional things like a trimpot for adjusting tremolo Speed and two trimmers for power amp bias.

Olivier's picture is intriguing, you can see some of the amp but I love how they've just taken a standard pedal and mounted it to the case:

http://olivier-grall.yusynth.net/instruments/Pianos/WURLITZER/wurli%20300%20rear.jpg

[Jenzz]

Hi all :-)

Since i have a 201 in for service (the 300 uses the same PCB), i will take some pics of the PCB tomorrow...

....stay tuned ...

Jenzz