Help! My 200 has a "hot spot" around F5 and it's driving me crazy!

[e23]

So, I have a "hot spot" around F5 and it's driving me crazy. The notes in this area are a lot louder than the neighbouring notes. It starts around Eb5 (where the treble pickups begins) get's loudest around F and then normalises around G.

I feel like I have tried everything and I can not get this sorted out.

I have suspected reeds, hammers, resonance in the harp, the tightness of screws... But none seem to be the problem. To find out, I swapped pretty much everything I could, without it making a difference.

Reinstalling reed brackets (2 reeds in one bracket): No difference

Swapping hammers: No difference

Putting a clamp on the harp behind the pickups: I tried this because it made a difference when I removed the entire harp and hit it lightly with the grip of a screwdriver to hear it resonate. Without the clamp, it had a certain ring, which I suspected might be the problematic resonance. But with the clamp, it was muted and did not have that ring. But when the harp was installed, it made no difference.

Loosening/Thightening harp screws: A small difference maybe, but nothing major.

Loosening/Thightening pickup screws: A small difference maybe, but nothing major.

Swapping reeds: The F5 reed sounded loud in the F5 slot (hot spot), but sounded normal in the C5 and A5 slots. The A5 reed sounded normal in the A5 slot but sounded loud in the F5 slot.


So, it seems to have to do with the slot itself, not the reeds or resonance, right?
If it was the reeds, the problem should have moved to other slots alongside with moving the reeds.
If it was a resonance problem, I would assume that problem would have also moved alongside moving the reeds, since the resonance should exite a reed acording to it's frequency/tuning and not it's placement in the harp, right? And I tried a clamp, tightening/loosening of screws etc. and it made no difference worth mentioning.

Does anyone have anything else I could try (non-permanent)?

I'm starting to think that my only option here is to (very carefully) broaden the grooves in the pickup to lower the volume of those slots. But that's a rather harsh and permanent modification (no backsies possible), so I want to avoid it if at all possible. From everything I've read so far, I'm probably going to hear it from you guys just for mentioning this

Please help...
Cheers

[pianotuner steveo]

Are you positive that the Reed in that slot is not shorting out to the pickup? You will see small sparks if it is. Try cleaning out the slot first. If that doesn't work, very carefully filing the side of the pickup (NOT the Reed) should solve the problem, but like you said, is not reversible without a spare pickup. This must be done with power disconnected, and just a tiny bit of filing at a time. Use a small metal file. Be sure none of the aluminum dust shorts out other pickups. This is a tedious job, but is possible. You have to remove Reed,file, install Reed and check, lather, rinse repeat unless you are lucky enough to get it right the first time.

WARNING: as you probably guessed,if you file too much, that Reed will be much quieter than the others...

[e23]

Thanks man! The slot is definitely clean.

Thinking about what you wrote: Why not slim the reed just a little? Sure, they are finicky and I'd have to add solder too. But at least they are easily replaceable and the process therefore would be reversible.

Cheers

[e23]

Steveo, you're the man!

I know, it's exactly what you told me NOT to do, but I tried it anyway. I went ahead and carefully sanded (no files!) the sides of the reeds (manually!), thereby slimming them down just a little to allow for more clearance in the pickup. I tried it on only one reed first, of course. And what can I say ...
It worked!!!

Again, thanks so much Steveo! You may have told me not to, but you made me think of it in the first place, so you get the credit, whether you like it or not    

It was tedious work though. Had to add solder to all the reeds I slimmed down and tune them again. And I may have to work on a few reeds a little more... But who cares. That thing is playable now, half way decent even 

Cheers!

[pianotuner steveo]

You should never sand or file the sides of the reeds, but at least it worked. The reason why you shouldn't do this is that it can weaken the metal,but it is far easier and cheaper to replace a broken Reed than a hard to find pickup that was filed too much. There must have been a solder burr or something on the Reed that was causing it to be too close to the pickup. Glad it worked out.

[e23]

This is weird. I managed the hot spot issue using headphones, but when I put the lid back on and use speakers, it's still there. Less harsh, but it's still there. So it seems to me like it actually is a resonance thing and using the speakers seems to amplify it.

No-one else who had to deal with that?

Cheers

[pianotuner steveo]

Possible bad speaker(s). I've seen that happen more than once.

[DocWurly]

Old thread.

The reeds in the section starting with D#-43 have distinctive features:

1) They are narrower than the reeds right below them. They should look different. Make sure you have the right reeds in those spots.

2) Typically, (but not always), the gap between the reed and pickup is narrower from D#-43 to C-64. According to my cheap Sears feeler gauges, a centered reed in this range will have a gap of .006 inch on each side, while the middle range will have a gap of .008 inch. (You might more or less accurate readings from a different brand of gauge, but you get the idea.)

Some wurly techs roll their eyes at my insistence on these gauges, but they give a much more accurate reading than what the naked eye can see.

If I were running into this problem, I'd assume an uncentered reed, or a solder tip overhanging the side of the reed. Carefully filing the sides of the solder tip, so it it smooth and doesn't overhang, is something you _should_ do. The fact that this improved the situation is a sign that you were on the right track.

Do NOT file the pickups, though (even though some early manuals and official Wurlitzer notes recommend this).


What eventually happened?

[DocWurly]

Thinking on this a little more... there is another mystery factor with what you are describing, and I _have_ encountered it.  That business with it showing up only when the instrument is fully assembled. Yes, I've known this to happen in the E to F# range on 200A's, especially those from around 1977.

It could be a resonance with the hum shield.

It could have something to do with speaker placement.

It could be a tendency related to the body design, or the air cavity space.

There is also a feedback/sustain tendency that tends to happen around F-21 or F#-22. I wonder if these issues are related.

But do check the things I mentioned in the prior post if the problem persists.