OK Hammond Docs...my beast has fallen silent...Help!

[Blues Disciple]

Hey gang,

 

My 1956 C3 is experiencing technical difficulties. Here is the description of the symptoms:

 

A month or so back, the volume started dropping or the sound would cut out altogether. I checked the tubes and all were fine except one. When you look at the organ, the last tube on the left in the row of the five or so tubes on the right side of the Preamp, (the tube is located right before the volume pedal spring) was loose. When I moved it, the volume would return to normal or come back on. Wiggling the tube worked for a few weeks. The volume would come back and stay that way throughout practice.

 

During that time though I noticed at one time, my lower manual was louder in volume than the top manual. Occasionally there would be some loud click sounds or static-like sounds as well when I played.

 

Last week I applied some Deoxit to the tube/socket and things improved. Then last night, it started acting up and at times, for a short time, when I pressed the Bflat and Eflat keys, a loud burping sound blurted out. Then it finally went mute and I couldn't get it to work again. I sprayed more Deoxit and still nothing. No sound at all. Pulled out the tube, reinstalled and still nothing.

 

The tube does get hot and you can see the orange light coming off of it, so it is getting juice. It appears that there is not any contact though in the socket. I am not sure what the tube name or size is as the original markings are gone. Our thought (my bassist has a Hammond too) was that either the socket is shot or the tube has a dead pin or two. My hope is that all it is...

 

Any thoughts? If you guys think it may be the tube I can either pick a new one at a Hammond place near here or can order one online. If its a socket, I could probably do the same, though the install would be either tough and/or pricey. Anyway to fix a socket without replacing it?

 

Anything I should check out before a diagnosis can be made? Any suggestions on what the problem may be just from my description?

 

You guys have been a big help in the past with the few problems I have had....hoping you can do the same again..

 

BD

Charlotte, NC

[MoodyBluesKeys]

Based on the service manual for B3/C3, the tube located as described is V4, which is a 12AX7. I spent over 25 years servicing electronic organs and other musical devices. A completely defective socket is possible, but I do not believe that it is likely.

 

It is much more likely that one or more of the original resistors, or maybe capacitors has gone defective. The 12AX7 is a two-section triode tube, that is just before and just after the variable capacitor that is used for swell volume control. Resistor values in this circuit are quite high, the two plate resistors are 330,000 ohms - it is very possible that one or both has gone up drastically in resistance.

 

In fact, on a preamp this old (50 years or so), it would not be a bad idea to have a skilled tech change every capacitor and all fixed resistors - although these parts are not nearly as easy to come by now as they were a few decades ago. If the original tubes are still working - LEAVE THEM, the tubes being produced today are not as well made as the originals. Low power tubes have been known to operate OK for thousands of hours of use.

 

I am listing the approximate tube pin voltages. However, unless you both have measuring equipment and are confident of your ability to make measurements without shorting anything or getting yourself in the electrical path, I would encourage you to have the instrument repaired by a capable technician. Format of the table is: tube pin - voltage. 1 - 140v DC, 2 - 0 v (and will make a loud hum when you touch with the meter probe), 3 1.7 volts, 4 & 5 are heater pins, they are tied together, and there should be 6.0 volts AC between them and pin 9, 6 - 140 v DC, 7 - 0 v - again a loud hum when touched with the meter probe), 8 - 1.7 volts DC.

 

This tube is the next to the last tube in the preamp electronically. V3, a 12BH7 tube, is closest to the volume pedal spring in the group of two tubes - it is the last amplifier that feeds to the power amplifier or Leslie amplifier. Voltages given for this tube are: pin 6 - 285 v DC, 7 - 0 v (will make some hum when touched with a probe), 8 - 12v DC.

 

WARNING: The maximum DC voltage in the preamp is 375 - enough to kill you. 110vac is also feeding the power transformer, again enough to be fatal. If you chose to check the unit yourself, be careful.

 

Jim Cason

Promised LAN Computing, Inc.

New Bern, NC

Kurzweil K2000VP, PC2, PC2X, K2661, PC3X

 

[Musicale]

Sounds like it needs a pro check out, as there could be a lot of components that have drifted over the years. Rather than one piece at a time repairs, in the long run you are better off getting a comprehensive check up. You can even replace the amp and preamp with new / rebuilt tube units or solid state, no problem. I just had my A100 and 2 Leslies completely refurbished and the set-up runs like a clock (pardon). During my experience, a lot of mechanical stuff needs to be disassembled (Vibrato scanner) and the key contacts , drawbar busbars etc. inspected and cleaned. When I saw what these beasts look like deep inside, I was completely amazed.

 

Regards,

[Blues Disciple]

Jim and Musicale,

 

Thanks for the responses. I have had my Leslie 122A preamp rebuilt about two years ago. I have had the Hammond Pre-amp checked out about the same time. The only fix I needed to do so far was to replace one other tube.

 

Jim---if I read your response right, it may be that one or more of the pins on the tube are fried. Would replacing the tube be the first logical step? And then if that doesn't work have a Hammond tech look deeper? I would hate to drop a couple hundred bucks or more on a total rebuild when its a $15.00 tube.

 

I will try the tube and keep y'all update. My experience may help out other Hammond players on the board over time.

 

BD

[retrokeys]

Since you have had the amp checked out as recently as 2 years ago and you weren't alerted to any potential problems down the road at that time, I think just trying a new tube is a good first step. The second step would be the socket. After that it is definitely technician time. You'll only be maybe 30 bucks out and I think you have good odds of solving the problem. Please let us know how it turns out.

[B3Nut]

The fact that physically manipulating the 12AX7 affected the audio points to a possible failure of the socket, sometimes the pin receptacles need retensioning. This is a hazardous job, however, since it invlolves inserting metal tools into the socket. If you don't know how to discharge *ALL* of the electrolytic capacitors in the preamp, leave this alone. Even if this restores the preamp to operation, replacing the fixed resistors and capacitors is a good idea as none of these components are going to be in spec. Fortunately the resistors and caps are for the most part pretty common, any electronics shop specializing in parts for tube-amp builders will have workable replacements. Triode Electronics has a good selection of parts.

[Musicale]

Yeah,

 

Worth replacing the tube and then the socket. At that point you're just a parts jockey, replace stuff until the problem disappears. The tube socket should not be a hard replace either, just gotta take the time. The general philosophy for a old unit like this is if it's workin', don't fix it. So do let us know of your progress. I'll think about it a bit, maybe there is some simple forensic type test that could reveal the fault.

 

Regards,

[Jim Alfredson]

Make sure the organ is unplugged and has been off for at least 5 days before attempting to replace the socket; or, if you know what you're doing, you can discharge the capacitors. They will hold a charge for a LONG TIME and can kill you.

 

Also, buy the best socket you can get. New, cheap ones are just that.

 

Those old sockets do not fail; I personally think you're barking up the wrong tree. It is most likely a bad componenet (resistor, capacitor) or perhaps a bad solder joint on the socket. Or maybe even a bad tube, but unless the organ is used 100 hours a week for 40 years, I can't see the tube going bad either.

[Blues Disciple]

Okay guys, here is an update:

 

I replaced the 12AX7 tube last night and did actually get some sound---very, very low volume though. When I turned on the Vibrato/Chorus rocker switches, that boosted the volume, but still too low to be heard much.

 

Haven't replaced the socket yet, though I did get a new one from Rick Prevallet today.

 

I did notice yesterday that some of the pins on the third tube from the right (facing the preamp) were a bit bent too. We are locating a set of tubes to test all of them just to double check it all.

 

I have located a Hammond tech who does "house calls" per se here in Charlotte, but am trying not to use him if I don't have to so as to avoid spending too much $$$$ if I don't have to.

 

So based on this new bit of information anybody have any thoughts on how to proceed or what the problem could be?

 

 

Any ideas or thoughts or info woudl be greatly appreciated.

BD

[Gary75]

Sounds like some resistors gone faulty in preamp. Had a fault where it was silent with vibrato off but normal volume when it was on, and replacing the resistors cured it. Do you have preamp schematics and can check the resistors out? My father is the Hammond tech, not me, otherwise I could be more helpful right now.

[Jim Alfredson]

It's near impossible to diagnose something like this over the internet. Unless you feel extremely comfortable working around extremely high voltages (the B+ in a Hammond is 400vdc), then just pay the tech. It's not worth literally killing yourself over.

[Blues Disciple]

Thanks for the info. Any other comments are sure welcome.

 

It looks like a call to the Hammond techman is needed as when it comes to anything more electrical than replacing a tube, turning on a switch, wrapping a cord up with electrical tape or plugging it into the wall, I am like Sargeant Schultz off of Hogan's Heroes---I Know Nothing, I Know Nothing!

 

BD

[MoodyBluesKeys]

Based on your own description of your technical abilities, and the availability of a pro technician - I would suggest that you have the tech take a look at it.

 

It is very possible that the tech may locate the problem and have it fixed in the first hour of the call; whereas you might spend days, wind up causing more damage, and still not have a working unit.

 

It is difficult to diagnose over the forum - there are a lot of potential causes; since replacing the tube did not cure it, I still feel that it is unlikely that the socket itself has failed, although possible. My expectation would be most likely that a resistor in the area has shifted value widely causing the voltages to be way off. Second likelihood would be an electrically leaky capacitor. Either requires having a good voltmeter and knowing how to use it.

 

Jim