Wurlitzer 200 Buzz - Lowish Volume

[Marcello7777]

I just got a Wurlitzer 200 and upon plugging it in, there is a loud buzz.  I thought it was the hum so I went ahead and did the buzz killer mod (to no avail).

Here is a video of it:
https://youtu.be/y5GW-39B4-U

My question is, I'm thinking of doing a complete rebuild of the preamp as the tremolo is also not functioning properly - I can kind of faintly hear it here and there in the buzz, but not really..  I am wondering if anyone has had a similar issue here and has fixed it?

Or would I be better off just going ahead and getting a vintage vibe preamp?

Any help is greatly appreciated

[pianotuner steveo]

Hi Marcello, I am more of an expert in the piano section than the amp section, but to me, it sounds like A: pre amp is working just fine. B: It still seems to be a grounding issue. Does it improve with a hum shield? Does it even have a hum shield? I seem to remember the non A 200 not having one. Also, the regular 200 does not have the separate preamp board on the Reed bar like the later models, it's a section on the amp board. If that were bad, you wouldn't get any sound.  And C: you need to adjust letoff on the keys. It seems like you have to hit them pretty hard - or at least some of them. The tool is sold on eBay.
I'm pretty sure the vibrato section might be the only issue. A broken ground here could cause both issues, hum and no vibrato. Always check things like this before spending money on parts that you may not need.

Have you carefully removed the amp board and inspected the bottom of it? It may just be a ground trace or two have opened up. Always unplug the Wurlitzer when touching the boards.

Hopefully someone with more amp experience will chime in on this thread.

[velo-hobo]

+1 To Steve's questions - where is the hum shield?

From the factory, a 200 would lack the reed bar shields that are located between the dampers and the pickups, as found on a 200A, but either model should definitely have the larger L-shaped hum shield that sits over top of the dampers. If your piano has neither shield, you are going to have a massive amount of hum like this - and no amount of money spent on a replacement amp will solve such a problem.

I've attached images of the hum shield and reed bar shield to better identify what I'm referring to.

As to the tremolo circuit, there are a few typical reasons why it might be malfunctioning on a 200-style amp:

*Caps and/or resistors in the trem circuit that have drifted in value to the point that the oscillator is longer stable. these passive components are cheap and easy to replace. You may need to try different resistor values to dial in the trem speed once you get it working. It can also make a "thumping" sound if it's not quite tuned correctly.
*Tremolo driver transistor is kaput
*Could be a bad potentiometer or else an issue of continuity in the wiring to the pot
*Some combination of the above
*Possibly none of the above

[velo-hobo]

Adding that another reason for massive hum could be bad or missing ground connection of the pickup output. If you disconnect the reed bar from the amp, you can remove the pickup noise from the equation as part of troubleshooting.

But you definitely need the hum shield, and I recommend adding the reed bar shields to any 200. Those make a big improvement in noise floor, IMO

[Marcello7777]

Thanks for your input on this guys.  I really appreciate it.

@Steveo - Thank you for the input.  It was doing the loud hum when I got it (the hum shield is off to the side).  I went ahead and re-flowed all of the connection joints on my board per your recommendation to look at all the connections on the board, and it seems to have solved the issue of the loud hum wohoo!!  A few of the connections were lacking a bit of solder.

Is this the tool you speak of?
Ebay Link

@Velo-hobo - I do have the hum shield, but not the reed bar shield.  This is what it sounds like after reflowing the connections on the preamp, and putting the hum shield back.  MUCH BETTER!  Still a bit of noise though.  You think I can further reduce this with a reed bar shield?

Here's how it is now:

As far as the vibrato circuit, any tips on where to start in testing / replacing?  I seen lots of people just doing a complete recapping and installing new transistors and whatnot.  I had some help previously tracing a problem on an oscillator for a Rhodes with an electrical engineer - which helped a ton!  As I am good with a soldering iron but reading these schematics is still not my strong suit - although I am slowly learning.

Lastly.  I appreciate you both in taking time out of your days to help.  It truly means a lot!

Best,
Marcello

[Marcello7777]

Also, my volume is at 100% to get a normal sounding volume.  Is this normal?  Or is something amiss?  I read the 200 series can be a bit quiet but just wanted to check

[velo-hobo]

That's great that reflowing solder joints helped resolve some of your problems. Some were never done properly at the factory, and on top of that, gig wear and thermal cycling over many decades can only add to the potential for issues in this regard.

The reed bar shields do make a noticeable improvement when added to a model 200, in my experience. Well worth it, IMO, if for nothing else than that they significantly reduce hum when you have the main hum shield off to adjust the tuning or action.

Re: volume being low. Could be something with the amp but it could also be that the trimmer pot for the pre-amp gain is adjusted too low or has some dirt/corrosion impacting signal continuity. That is the part that looks like a plastic wheel, soldered to the amp PCB to the right of the reed back input RCA jack. Mark the current position somehow and then try adjusting it to your taste. Too much gain can introduce distortion, but you might like it a little crispy sounding.

(Edit to add: if the signal crackles when you adjust this trim pot, it could benefit from some contact cleaner. you might spray some in there anyway, even if it doesn't seem to be a problem)

The main trem parts are as follows:
TR-4 - driver transistor
C27,C38,C44 - nonpolarized poly/film caps, all .12mfd/75V
R32,R33,R43 - resistors, various values - R32 is the primary one for adjusting the tremolo frequency

Check the function and connections/continuity of the trem potentiometer first. If the pot isn't working or isn't properly connected to the amp, the trem won't have any effect on the output.

The resistors and caps might be fine but they are cheap and widely available. I wouldn't bother replacing the transistor before doing the other components, unless you happen to have spares on hand already, or are placing an order with a specialty supplier that has these transistors.

Old-style carbon comp/carbon film resistors can drift in value with use and age. If they drift far enough from spec, it can detune the oscillator network causing it to become unstable and cease functioning. In some cases, replacing the resistors might be all that is required to get the trem working.