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Fixed it!

Should have thought of this sooner, but since I was reading 0V at the base of T1, I checked if it was shorted to ground - sure enough it was!

After a bit of looking I saw a component lead that had got caught between the board and the chassis.  Snipped the lead and now it sounds great!

Still have a bit of work to do in there, but for now I'm going to enjoy that it works after being out of commission for a bit.

Thanks again to everyone for all your help!

Hi :-)

All of these transistors will work (watch for different pinout!), but since this is the first stage, a low noise typ should be the choice. I would recommend MPSA18 or 2SC1845 for the first stage (again, watch out for different pinout)....


Jenzz

Ok, I just put in a new transistor to T1 (I ordered these).

Still no sound, and I'm getting the same readings at the legs of the transistor as before!
E: oscillates from 0.15 - 0.3V
C: 15.7V
B: 0V

Any ideas what could be happening in there?

Hi :-)

Since the input buffer (T1) stage draws no significant current (not voltage drop accross R12), i think T1 will be damaged.

I would also recommend the change C11 (filter) and C6 (feedback). Electrolytic caps of this age are prone to high leakage, loosing capacity or being shorted.

Jenzz

Wonderful, thank you!  I'll order a replacement right away.  I believe I already replaced those caps earlier (I'll check when I get home).  I will eventually replace all of the big old red capacitors in the amp, they are very old...

Searching for a replacement - when I searched the part number, this transistor came up: https://vetco.net/products/2n3904-bc547-pn2222-2n4401-npn-transistor-nte123ap

Does that look like the correct replacement?  Not sure where else to find information on which transistor is in there.

I appreciate you!

Just replaced practically all the resistors in that part of the circuit (R27, R28, R29, R30, R31, R32, R33, R34, R36 - and I had replaced R35 and R37 earlier which initially caused this issue).  Still no sound, now reading 15.6V at the collector of TR1 where I want to see 12V.

Is the transistor not doing its job anymore and in need of replacement?

Always grateful for all the excellent help I get here!

Hi :-)

Did you check the cable from the RCA jack going to the pickup system? What about the voltage directly at the pickup electrode? Remember that there is an additional 10Meg in series, so voltage reading will only roundabout 70 V.

Since you have a good signal when plugging into the phono: Do you obtain the marked 12V at the collector of T1 ?


Jenzz

Ok I am getting 83.3V at the pickup electrode.  Surprised because I thought for sure there's a bad connection somewhere in the RCA jack!  I'll replace the RCA cable with a new one just in case.

Aha!  Readings at TR1 are all wrong: I'm getting 16V at the collector, 0.28V at the emitter, 0V at the base.

Should I start replacing resistors in that part of the circuit?  Looking at R4, R7, R8, R9, R12.

(Reading at the collector of TR2 is 9.8V where it should be 7.8.  The readings at the emitter and base of TR2 are fine though)

Many many thanks for your help!

Just took some voltage readings.  I'm getting 150V where I should be getting 180 (on the other side of R1).

Any ideas on how to fix this are greatly appreciated.

Thanks!

Hi :-)

This is quite normal. Keep in mind that the 180V voltage is fed via a 2M2 (42) resistor into the last cap (44).

If you connect a multimeter, the input resistance of the multimeter (10Meg in most cases) will form a voltage divider with this 2M2. The result will be a roundabout 150V reading at C44.

Jenzz

Thanks for this!  Good info.  I started replacing some components between the transformer and keyboard input (R41, R42, and R45), hoping that would help the voltage get back to 180, but maybe I don't need to worry about that.

Any other ideas what might be causing my issue?

I'm able to inject a guitar signal into the phono input on the circuit and it comes out of the speaker clearly.
I'm getting +-32.5V at the output section.
Can't help but think the issue is somewhere in the connection between the keyboard and amp.

Any ideas are greatly appreciated!

Cheers

Thanks.  Hope it's not the transformer!

Just took some voltage readings.  I'm getting 150V where I should be getting 180 (on the other side of R1).

Any ideas on how to fix this are greatly appreciated.

Thanks!

Hello all,

Back working on my wurly after a while.  Right now dealing with no piano sound coming out of the speaker!

The piano had been making a fuzzy sound in the speakers every time I turned it on, and generally low volume that cut out sometimes.  I opened it up to replace the components from the vintage vibe kit.  I started by replacing R3 and R5 (see attached schematic).  Tested for continuity at the terminals, all connections seemed fine.

Then I noticed a loose solder connection between C2 and the input RCA jack.  Convinced this was the cause of the low volume issue, I replaced C2 and R1, the resistor that's also attached to the input RCA jack.

Now when I plug the amp in and turn it on, the pilot light comes on, the same fuzzy sound comes through the speaker, but I get no audio from the keys.

Any ideas what could be wrong?

One more thing!  I'd like to modify the headphone jack to be dual mono instead of only coming out of the left channel.  I'm doing some research on this now, but tips are appreciated.  Thanks!

Thanks so much to everyone for your help.  I'm a teacher, so I've finally been able to get back to working on my wurly on my summer break.

I adjusted the let off on some keys and that really helped the action.  Forgot to lube the action centers first, so I'll do that soon and then readjust the letoff on keys as needed.

I mounted the power resistors above the board, and that's working great.  No smells, no noise.

I'd eventually like to replace the can caps, but since the piano's working well now this isn't a priority.  But does anyone have advice for mounting/wiring replacement caps when the time comes?

The vibrato isn't very deep.  I'm thinking that there might be some light leaking under the enclosure for the lamp/photoresistor coupling.  Any tips on how to get that as close to stock as possible?

Thank so much for everyone's help!

Maybe someone replaced the tube amp in a 720A?  Here's a picture of the badge

Thanks for the tips!  The hum is gone, but there's still some crackling and fuzzy sounds most times I turn it on and play.  I have some time off work in a couple weeks so I'm going to replace more electrical components then.

I want to replace the can capacitors.  I ordered electrolytics with the same capacitance, but do you have any tips on where and how to mount the replacement capacitors inside the chassis?

Keys that have to be hit harder are usually letting off way too early. The Letoff tool is available on eBay. This is the single most common action adjustment needed in Wurlitzers.

Thank you, I see the letoff tool on ebay for the 720s.  Messaged them to make sure it'll work for mine, then I'll order it.

Thanks for all your input.

I lifted the resistors a little bit above the board and that helped a lot with the burning smell.  Makes sense that they shouldn't be in contact with anything when they're that hot!

And I'd love a copy of the service manual.  I'll pm you now.

Thanks again, this is super helpful!

Here's a picture of the high watt resistors.  The green ones get the hottest when the amp is on, and they look a little sickly and twisted.  That's my best guess as to where the burning smell is coming from.

I had been testing it with the lid removed, and I'd also wondered if the hum would go away if I put the lid back on.

But then yesterday I turned it on, same as I had before with the lid off, and it was dead silent.  The piano sounded great and clear through the amp, and there was no hum.  Amazing!  I'm not sure what changed, but it sounds great.

Still a small burning smell, so I just soldered the high watt resistors straight to the PCB, and it's still very quiet.  There's still a slight burning smell, but I'm thinking that's just the smell of the resistors getting hot, and that I didn't notice it before because the lid was always on?  Either way, I feel better knowing that those components are making a solid connection with the rest of the circuit.  And in the future I may replace them with higher watt resistors and see if that helps.

I'm going to pause replacing electrical components for the time being because I'm very happy with the sounds, but I have a couple more questions:

-The little cap that goes over the coupled LED/photoresistor came off.  Right now I have it taped onto the board, is there a better way to attach it?  The glue/adhesive between the LED and photoresistor has also come undone, is there a best way to reattach these?    These are ocmponents 20 and 21 in the attached schematic
-You mentioned a shield cable that's attached to the lid screws.  I'm attaching an image of a shield cable at the back of the piano that appears to have been cut.  Should I reattach it?

My next step is to adjust the action on the keys.  As I mentioned, some keys need much more force to play than others.  Also some keys are not damping properly.  Is there a guide to performing this kind of maintenance?

Thanks for all your help!

I'm restoring my 720A (B era) - see the doc wurly page here: https://docwurly.com/700-series-consoles-keep-em-straight-720-720a-720b-726-b/
It's the solid state version with a 140B amp.

The main issue I'm having is hum in the speaker.  Also when I first switch it on, there's a fuzzy sound that comes through the speaker, and intermittently there's some fuzzy sounds and pops that come through the speaker.

So far, I've replaced all of the polarized electrolytic caps, as well as some of the resistors.  I tied in and soldered some of these components into the leads of the original components, and there's a slight burning small when the amp is switched on which I bet is caused by these tie ins.
I also removed the cable that runs to the phono input, which reduced some noise and increased the clarity of the amp.  I also replaced the built in power cable with an IEC port and removed the "death cap" that runs from the 120V power source to the fuse.

I'm still planning to:
-solder the replacement resistors straight to the circuit board to try to get rid of the burning smell
-replace the can caps with electrolytics mounted inside the chassis (I have some ideas of where to put the replacements, but suggestions are appreciated)
-replace more caps and resistors (I have ordered this kit from Tropical Fish Vintage and haven't installed all of the components yet: https://www.tropicalfishvintage.com/keyboard-parts/wurlitzer-140b-amplifier-rebuild-components )
-I also want to get into the volume and tone knobs on the cheek block and apply contact cleaner.  Does anyone know how to access these potentiometers?

Do you have any other suggestions for removing the hum from the amp?  Am I on the right track?

I also will need to make adjustments to the action of the keyboard, but I want to take care of the electronics first.  Some keys require more force to hit than others.  There are also some keys that are not muting properly.

I can update with some photos later if that would be helpful to see what's going on in and around the amp.

Many thanks!

Wonderful, thank you!

I replaced them with the 1N5401 and the amp is no longer blowing the fuse.   It does have some other issues which I will post in a new topic.

Thanks again!

Hello!  I am working on repairing the amp in my 720A "B era" console Wurly (see https://docwurly.com/700-series-consoles-keep-em-straight-720-720a-720b-726-b/)

I accidentally shorted the rectifier diodes and blew a fuse.  I'm attaching a picture of the shorted diodes and a pdf of the amp schematic (the diodes are D63, D65, D66 and D67 on the schematic).

If I need to replace the diodes, what should I replace them with?  Anything special?  The diodes are marked "6743".

Very happy to find this forum, I've just been bugging the kind people at the Tropical Fish Vintage Wurly hotline and I think they'll be happy not to hear from me for a second 

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