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Messages - David68

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I've done a few, and it's always a bit of a mess. What products/processes do you use to re-glue a Wurlitzer nameplate?

I've removed the old glue, which is the worst part.

This 200A ran all day in the shop with no more crackles, so it seems it was a failing resistor in the 150V supply.

I hate these problems that only pop up every half hour or so and then disappear again. Very hard to catch it in the act.

I have inspected solder joints.

I ended up replacing all five 150V supply resistors on the main board, and, thus far, no more crackles. I'm going to run it for a few hours while I work on other things to make sure that solved the problem.

On the diode on the reed bar preamp, it's there to turn on in the event that the signal input goes too far negative, as I suppose it might as the 150V supply comes up. The 25V reverse rating might be so that it shorts to ground in the event that the input DC blocking cap fails. So I think any diode would work, but it actually has a low PIV rating because it's designed to fail in the event of a cap failure.

I have a Wurlie 200A on the bench that's been driving me nuts with an intermittent crackle I've thus far been unable to isolate. For one, it's very intermittent. The piano will work fine for a while, then crackle for a bit, then go back to working. I have rebuilt much of the reed bar preamp with new transistors and new resistors. The single diode and two 100pF caps are original. The 150V supply is unchanged. The noise tracks with the volume control, so it's something upstream of it.

As far as I can tell, it's not a pickup short. I've checked reed alignment and blew the whole thing out with compressed air. I've jiggled wires and resoldered some. Playing the piano or not playing makes no difference. I've chopsticked components with the piano on. None of these produce the noise, so I'm thinking it's some PCB component failing. I know that high value resistors sometimes open up, so I'm thinking of shotgunning all 5 resistors in the 150V supply.

As for the components on the reed bar, is there anything special about the diode? Will a 1N4148 work as a replacement? (I have those in stock.) It's rare to see ceramic caps fail at low voltage, but I suppose it could happen.

Any other ideas or diagnostic procedures to try to get to the bottom of this? The frustrating part is doing the work and not being able to tell immediately if you've solved the problem. You have to wait for it.

Thanks in advance for any suggestions.

The Wurlitzer Electric Piano / 140 keytop replacement
« on: March 07, 2019, 05:49:52 PM »
I have an abandoned Wurlitzer 140 in my shop, and, though playable, the white keytops pretty much all have multiple cracks in them. Cosmetically, it looks horrible. 

How bad a job is it to try to go in and do a complete keytop replacement?

The Wurlitzer Electric Piano / Re: Harp ringing in 200As
« on: February 24, 2019, 04:01:24 PM »
I rebuilt most of the reed bar preamp to lower noise, including resistors, transistors, and electrolytic capacitors. All soldering was carefully done and double-checked because the goal was to get rid of an intermittent crackle, which was successful.

The 0.022uF film cap and two 100pF ceramics are still original. I guess I can tap on them and see what happens. I know that Class 2 ceramic caps can be microphonic.

The Wurlitzer Electric Piano / Re: Harp ringing in 200As
« on: February 23, 2019, 02:26:03 PM »
Thanks for the replies. I think I've figured out the difference between the two. The 200A with less harp noise has a Retrolinear amp I installed. The one with more harp noise has its original reed bar preamp PCB, and I think that the reed bar preamp is itself slightly microphonic -- and screwed directly to the harp. The Retrolinear amp does not have active components mounted to the harp and is thus more isolated.

The Wurlitzer Electric Piano / Harp ringing in 200As
« on: February 20, 2019, 12:28:33 PM »
I've got two 200As in the shop at the moment, both from 1977. With one, when you hit a staccato chord, you hear a bit of a metallic ring after the note that appears to be coming from the harp itself. You hear it even if you just tap the harp from the side. It doesn't appear related to damper tension, nor is it from the shield. The other 200A produces the same sound, but it's not as noticeable.

Is there any way to treat this issue on the one that has more "ring" after a note?

The Wurlitzer Electric Piano / Re: Wurlitzer 200A volume issue
« on: February 18, 2019, 09:31:44 PM »
Much more dangerous than the reed bar supply, which is very much current-limited through large-value resistors, is the exposed 120VAC on the back of the volume control.

Did the volume pot ever work? Is it possible that someone hard-wired it out of the circuit? I've seen stranger things.

The Wurlitzer Electric Piano / Wurlitzer 200A +15V supply question
« on: February 17, 2019, 04:31:57 PM »
I'm working on a 200A with its original amp, and the +15V supply is a bit on the low side at around 14.2V. I realize that this is not a precision device, but I was wondering if anyone knew exactly what provides the voltage reference for the regulator chip since I don't know what the circuit is inside the chip. Will the 15V supply be off if R54 and R55 (10k 1%) have drifted?

This one turned out to be a broken pickup wire, which I managed to splice and reconnect. I assumed too much when I started out.

Still, the volume pot is marked 50k, but is only 11k.

Parts, Service, Maintenance & Repairs / Piano Bass Control Circuit
« on: July 09, 2015, 11:15:25 AM »
I've got a weird problem that I thought would be a 5 minute fix.

It's a 1980 Rhodes Piano Bass I've tuned and voiced before. Suddenly, its output dropped to almost nothing. Output at the harp is fine, but as soon as you plug in the RCA plug, it drops to almost nothing. The cable is not shorted, and continuity is good everywhere.

The control circuit appears to be stock, but it doesn't match the one Piano Bass control circuit I've seen online. The tone control is a 250k linear pot, but the volume pot is a 50k shunt-type control that works by shunting the signal to ground through a 0.22uF cap. What's strange is that this "50k" pot measures 11k (out of circuit) and no amount of blowing or flushing it out changes that. I've seen pots that cracked to an open condition, but I can't figure out what would have changed its value like this.

Is this the typical later Piano Bass output control circuit?

The Wurlitzer Electric Piano / Re: 206A conversion
« on: February 05, 2015, 08:27:03 PM »
I did a 206A vibrato retrofit a couple of weeks ago. It was tedious, but not a challenge.

I'm trying to remember: Are the leg mount brackets on the portable pianos something you can buy at a good hardware store, or are they a special-order item?

I'm trying not to get stuck needing some part I don't have so I can finish the job quickly.

The Wurlitzer Electric Piano / 206A conversion
« on: February 05, 2015, 11:08:17 AM »
I have another 206A coming in, this one without the base and sustain pedal.

I'm trying to put together a list of what needs to be done, and I'm wondering how people generally go about retrofitting a sustain pedal to the 206A. Is a sustain pedal assembly all you need, or are there other hardware differences or missing parts I need to be aware of?

I suppose that legs and leg hardware need to be figured in.

Retrolinear knobs it is.  :)

I just finished a 1973 Pianet N restoration, so I wish I could help, but it wasn't out of tune at all. My sense is that Hohner didn't expect them to go out of tune, or, if they did, the idea was to install new reeds.

Pianets have been non-repairable for so long that there doesn't seem to be a great body of knowledge on how to fix these issues.

I was also thinking of getting a metal sleeve, like a length of brass tubing of the right size, and epoxying it around the outside. I'll have to check control panel hole clearances, but something of the right internal diameter can be ordered from McMaster.

Parts, Service, Maintenance & Repairs / Gluing cracked Wurlitzer knobs
« on: January 21, 2015, 11:26:38 PM »
One of the control knobs on a 206A has three cracks in it.

Has anyone come up with a good way of fixing these so that the cracks don't open back up? Glues don't always hold that well to plastic, and I'm thinking it might need to be reinforced somehow. My grandfather was fond of using fiberglass cloth and epoxy.

The Wurlitzer Electric Piano / 206A harness wiring?
« on: January 20, 2015, 02:19:32 PM »
Is there a schematic that shows the speaker/lower unit harness wiring for the 206A?

I've found the diagram for the 206, and it seems mostly the same, but not entirely. It's not vital that I have this documentation since I can figure it out, but it would be nice.

I slept on it and decided to try an experiment. The really intractable problem was with one note, an F, so I decided to swap that F key with another F key an octave above.

Problem solved.

This seems to be a frustrating issue for many.

I'm working on a 1973 Suitcase Piano 73, in very good overall condition--seems not to have been played that much.

I've got two notes in the lower range, 13 and 14, that sound dull if played hard. Interestingly, this piano has a mix of hammer colors. On most, the plastic is a darker tan, and these all work fine. There are a few made from lighter-colored plastic, and these are the ones that are causing trouble. Several of them would stick above the stop-lock position, a problem that seemed to be caused by plastic burrs at the rear edge of the underside of the hammer. Very careful deburring and silicone treatment cured the sticking problem, but on two notes, the stop-lock position is still higher than the adjacent hammers and damps the strike.

Is there any way to adjust the escapement on one or two hammers? I'm at wits end.

Parts, Service, Maintenance & Repairs / 80W Suitcase buzz
« on: January 13, 2015, 12:58:37 AM »
I've been working on a restoration of an 80W Peterson Suitcase, and I did a careful job of rebuilding the power supply, especially the regulator board, to get everything as quiet at idle as possible for a studio. The base is extremely quiet on its own; however, when I plugged the preamp in, I got a buzz that I tracked to interaction between the power transformer and the audio cables to the power amp modules. I'm able to minimize the noise via wire dress, but I was wondering if anyone has come up with any other creative solutions to this problem. It seems to me that one of the power amp modules is a bit too close to the power supply's power transformer for lowest noise.

Parts, Service, Maintenance & Repairs / Re: Pianet N Restoration
« on: December 15, 2014, 01:08:52 PM »
Oddly enough, I have another Pianet N in the repair pipeline, and this one has a burnt-out vibrato lamp.

I know it's 12V 50mA incandescent, but does anyone know off-hand what basing/size standard this is? I think it's an E10 base, but I'm not 100% sure.

Edit: It is an E10 T3.25 10x28mm 12V 50mA 0.6W lamp, but this appears to be very much an oddball lamp in the United States. Seems to be much more common in the UK.

There's one US source that wants $6.80 per lamp with a $40 minimum. Any better options?

Parts, Service, Maintenance & Repairs / Re: Pianet N Restoration
« on: December 14, 2014, 01:22:06 PM »
The previous owner may be blameless on this. Many of the N's seem to suffer from keys that curve slightly over the years. (If you look carefully at your Pianet, you'll probably see other keys that show that characteristic to a lesser extent.)  I've heard a couple different theories about what causes this.

Interesting. The other keys on this one are pretty straight, but this one key was so warped that it rubbed on its neighbors, rendering it unplayable.

Parts, Service, Maintenance & Repairs / Pianet N Restoration
« on: December 13, 2014, 09:26:19 PM »
I'm finishing up my first restoration of a Hohner Pianet N (~1973) using the sticky pads from Ken Rich.

The veneer is in good/fair condition, but very dry, so I'm wondering what sort of products can be used to bring back some sheen to it.

All that's left to do at this point are repairs to the volume pedal. The pivot is missing, so I'm having a friend with a machine shop make me a new pivot; fortunately, I know someone else with a Pianet N, so I was able to borrow a volume pedal to copy that part. Unfortunately, the pivot is 6mm, not 1/4", so he's having to order some 6mm steel to make it.

Some others who've worked on Pianets advised me to make sure the inside was very clean.

One challenge was straightening a warped white key. It looks like someone reattached the spring mount at some point and did something that caused the key to contract on one side. I had to heat it very carefully while applying gentle pressure to straighten it out.

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