No sound from CV and PR-40...

[Brentaver]

Recently purchased a CV with a PR-40 for $150. I knew it had no sound when I bought it, but I couldn't pass these up for the price.

Anyway, the guy I purchased it from said the tubes need to be replaced. How should I go about actually finding out why there is no sound? There are no Hammond Service techs in my area that I have found. I have no problem working on the organ myself and am confident I can get it to work, just graciously asking for your input.


Thanks!

[Alek Z]

Wow that's a great deal! There's a pretty decent procedure of diagnostics you'll wanna go through. Before anything else I'd recommend using a power amp/cabinet that you are certain works, so you don't have to worry about if the tone cabinet doesn't work, and then worry about the tone cabinet later. Try it out at that point, and maybe the organ is fine and it is the tone cabinet. First off does it run? If it does, go and check that all tubes in the organ are lit. If you're trying to save money just replace the ones out (if there are any), or just buy a whole new set like I'd recommend. That is the most likely cause, but it could also be problems in the drawbars, preset keys, the amp, the transformers, cords, there's a plethora of possible problems. If it doesn't run, then that's a very obvious problem for not making sound. Could you provide some more information on the condition of the organ and the conditions under which it doesn't produce sound?

[muckelroy]

If this organ is stock, it won't work with an external amplifier unless you give it about 200V DC power at the B+ terminal of the organ's preamp.

Start with the generators being sure they start and run. You can clip lead an external amp at the rheostat box to listen to it sans-vibrato.

You can buy an external B+ power supply to test the preamp.

The preamp is is one of the more challenging ones to work on because it's kind of a rat's nest. It's narrow and deep, with 2 or 3 layers of components/wires. It may work but it should have its coupling capacitors replaced, at minimum. The unfortunate part is that some of the coupling capacitors are at the “bottom” of the chassis (when turned upside down). It's for this reason that when I worked on my CV preamp, I decided to replace almost everything.

The PR-40 will need a lot of attention too, if you plan on using it. Tube count alone makes it costly to get new tubes for them, but they are worth it when they are working well.

I wouldn't expect this to be an easy learning curve if it's your first time to work on tube amps or preamps. There are lots of resources at your disposal, and research is your best tool before you get started. If you can find a tech who will help you, that's almost always a safer option if you want to ensure it's done well.

[Brentaver]

Thanks for your replies. As soon as I get home from work, I'll give a more in depth synopsis.

I don't have any other parts or power supplies. I have a T-524 that I'm in the process of modifying and an R-182 with a broken spring coupler in the TWG crankshaft. Both, as you know,aren't tube, so this is my first foray with tubes.

But, yes I will provide more information tonight!

Thank you both!

[Brentaver]

After some looking, one of the 6SN7 tubes is damaged. I will order a new set next week and see where it goes from there.

Is there a particular thing I should know regarding tubes to buy? Like I said, I'm new to tubes so any information will be greatly appreciated.

[muckelroy]

How do you know it is damaged? Glass cracked? Is it all foggy/white inside like it lost its vacuum?

Both the organ, and the tone cabinet probably needs a lot more than just tubes, but you can buy just about all of the tubes you need from various online sellers. You should start by reading the Hammond organ service manual HOOO-000495, or better yet, the high resolution version JoeyB3 put together, called Hsm495-2016. Internet searches will take you pretty far to find all of this stuff. If you want to go deep learning how tubes work, read the Radiotron Designers Handbook, 4th edition, also available in PDF form.

If you don't want to mess with the 5 tube preamp, Trek II sells a solid state preamp that will work. From there, your main concern would be to restore the PR-40, or to find a different amp / tone cabinet or Leslie to play through.

Does your generators start and run? Is the AC wiring to the organ and lamp socket crunchy and in need of replacing? There's a lot to think about before messing with the preamp.

[Brentaver]

Ok, sorry for such a late response. The run motor will not stay running. I have finally gotten sound from it from holding the start and run (not for a long time). But, where should I go from here?

[skydawg]

The generator has been oiled and spins freely?Also the felt in the tub above the run motor.

[Brentaver]

Skydawg, yes I have added an entire tube of Hammond oil to the funnels over the course of a month or so. I made sure the oil was making its way through the tubes and into the generator and the tub on the motor.

The generator spins freely. The oil threads are intact. I can get it to start but it cuts out after a couple seconds, then floats to a stop. I can get sound from it but after I let the start switch go, the pitch winds down until it stops completely.

[David Anderson]

You may have a bad run motor. It's more common in these older organs. First, check to make sure you're getting power to the run motor. Just flick the run switch on. Don't worry about starting it. Check for 120VAC at the terminals where the wires from the run motor connect on the panel on the left of the tone generator from the back. If you're not getting power, fix that. If you are getting power, test the motor by trying to turn it by hand. You should feel resistance, and the motor should flip from one position to another after you overcome the resistance. In other words, it will want to stay stopped in certain positions related to the shape of the magnetic field. If you can turn it without resistance with power applied, then there is no magnetic field, and you likely have a bad run motor.

[Codean]

I just had this issue with my CV that wasn't used for about 20 yrs, my run motor was bad, a few different ways to test, unsolder the wires to the power terminal and going across the wires , you should get 90 or 180 ohms. What I did was disconnect the flywheel spring, flip the run switch on and feel if you have resistance like David mentioned. Run motor wasnt that bad to replace although it looks very tight in there. Instead of removing the preamp (like I did at 1st), you can just remove that wire termonal and move it out of the way, that gives you more room to remove the run motor. My only issue was the vibrato scanner and the oil wicks, kind of hard getting that all back into place. But I was able to get it in and my CV is screamin now. My only issue is I have a 222 Leslie that my speakers are stuck on fast speed where the forum really helped with troubleshooting. Hope this helps

[Brentaver]

Ok the run motor tested fine. Not sure what to check next. I heard something about testing the wirewound resistor but not sure exactly how to test it.

[David Anderson]

I would next test that the CV preamp is getting B+ voltage from the tone cabinet. Then, if there is no B+ voltage, you need to find out if you have B+ at the PR-40 and, if so, where the break in the chain is. If you have B+ and the tone generator is running, this becomes an issue of signal tracing, i.e., figuring out where the signal is being interrupted. Hammond techs aside, are there any guitar or related tube amp techs in your area that could help you trace the problem?

I assume you know that you need to have some reverse-colored key locked down to get any signal, right?

[Brentaver]

B+ tests fine when run switch is flipped. The preset key is pressed. I get sound if the start motor stays on but as soon as I let it go, it slows down.

[muckelroy]

B+ tests fine when run switch is flipped. The preset key is pressed. I get sound if the start motor stays on but as soon as I let it go, it slows down.

At this point, either your run motor is bad, or you have a faulty run switch. It's also possible that you have bad solder joints on your line panel.