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Topics - gacki

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The Wurlitzer Electric Piano / complete Wurlitzer 200A service manual?
« on: September 06, 2021, 05:44:17 AM »
I wonder if there's a really complete service manual somewhere out there?

The ones I have seen so far (vintage vibe and others seem to miss at least one page, possibly more.
The go up to page number 65 (which is the beginning of the description of the 200A amplifier) but there are clearly the following page is missing since the description stops mid sentence.

(A cursory search didn't turn up anything, so if this was discussed already please point me to the thread in question. Thanks.)

I'm more of a Rhodes person but was asked by a couple of fellow musicians to work on their Wurlitzer pianos. Recently I already posted about my experiences with a 200; now it's a 200A.
I did a 230V conversion that went pretty flawlessly although I wish the the transformator had longer primary leads.

The amp is generally sounding fine with the appropriate "bark" and with practically no hum (although the hum shield isn't installed yet). This radically changes when turning up vibrato.

On the 200 it appeared to me as if the vibrato circuit was attenuating the sound; on the 200A it seems as if the sound is boosted instead. Is that correct? It quickly goes into overload and also exhibits lots of hum in those louder portions of the modulation cycle.

Is this normal? Is there something that can/should be done except turning the volume down before turning vibrato up?

Hello everyone; I'm currently working on a 200 that had some amp problems.

It uses a mid-production version of the amp. Originally the amp had a number of problems: when switching it on R10 was emitting "magic smoke" and there was huge ripple on the 44V rail (around 10V). TR1 was swapped for a BC168H (which was highly sensitive to any movement and vibration). R8 was open. There were some modifications (including an additional cap that was practically leaning against the transformer leads) and the aux out wasn't working. TR9 and TR10 seemed to be shot.
After swapping out TR9 and TR10 (and TR8) the power amp started to work and R10 wasn't smoking any longer (I swapped it anyway since it probably was stressed). I recapped the whole thing, installed new power resistors, removed most of the later mods and installed the resistors for the final revision of the aux out. TR1 first got moved to one of the other positions but meanwhile got swapped for an NOS part.

In general it seems to work rather well now but I'm still unhappy with hum and heat generation. From what I've read I know that there are limits to what can be done with this type of amplifier. I would like to know if I'm close to those limits.

The preamp seems to work rather well; it has some slight hiss and minimal hum (the unit has the reed bar shields). When I'm using the aux out through a DI box it's sounding quite good.
The power amp on the other hand still hums slightly.
I'm concerned about the ripple on the 44V rail. This is around 1.8V p-p before R73; less behind it. That ripple is also still slightly present at the base of TR8. In general TR8 (the driver) seems to cause or worsen this: without TR8 the ripple is around 300mV. Power through TR8 is around 125mA. Simultaneously the power resistors get VERY hot; I think R7 already shows some discoloration. This is happening with both the new TR8 and the old one. I'm actually somewhat surprised that the hum isn't dramatically worse given the (comparatively) high ripple.

(There also is the issue with the transformer leads; however I don't think the ripple problem is coming from that. Even worse, there are four transformer leads running next to the amp because its a 220V model.)

So is this as good as it gets? Or can this still be improved?

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