Electric organ volume pedal controlling tremolo... Uh, help?

[Firepowerforfreedom]

Well, after a thorough rooting around inside my old Conn Caprice 427, I've fixed quite a few of its irritating defects. However, one big problem still remains: my pedal controls (or rather, controlled, until I got the great keyboard running again) the tremolo, rather than the volume.

I found out the pedal runs into the amp in two places, both connected with RCA jacks (and I thought they only used those things on the outside of audio equipment... silly me). The rest of its thick, black cables run up towards the switches on the left side of the swell keyboard.

After rearranging the vacuum tubes in the back, I have barely any tremolo and no control over it to speak of. And the pedal still doesn't work properly. However, the rest of the organ sounds much louder and crisper, albeit annoyingly so. Any clues on where to look for the problem?

If it's not painfully obvious already, I'm a total audio newb.

[Steerpike]

You can't just "rearrange" the tubes willy-nilly. Each one has its own specific socket. Best check you have the right tubes where they are meant to go... if you swapped something like an 12AU7 with a 12AX7 you might get sound - likely distorted, but other functions won't work correctly.

[Firepowerforfreedom]

Originally Posted by Steerpike

You can't just "rearrange" the tubes willy-nilly. Each one has its own specific socket. Best check you have the right tubes where they are meant to go... if you swapped something like an 12AU7 with a 12AX7 you might get sound - likely distorted, but other functions won't work correctly.

I took note of that before I ever switched them. All of the tubes I switched around were 12AU7's. There was one 12AU7 that was a little different than the rest—its label was orange and the rest were green, but all were Conn-manufactured.

I didn't mess with any of the other tubes.

[indianajo]

Before taking the back off the organ, read the sticky thread at the top of the tube amplifier forum about tube repair safety. Tubes have lethal voltages, you have to keep your hands out when the power is on and discharge the capacitors with a tool before putting your hand in again. That said, you might try swapping the RCA plugs for a quick fix. If that doesn't work, you need an AC voltage detector, either a DMM with a 2 VAC scale or lower, or a 20 Mhz (cheap) oscilloscope with a scope probe. Both will need two clip leads for attaching the ground to the chassis and the plus to the point of investigation. Look for the output of the section that you want going to the pedal- turn it on and off, and look with the detector to make sure you have the right one. Clip the plus after the DC blocking capacitor, not right on the plate itself. Then trace the wires going to the pedal and see if it is the same one. If not, trace the wires and see why not. Obviously the pedal is connected properly on the output side to the power amp. When tracing wires, notice that the plates of tubes are the outputs, and the grids are inputs. You can see tube schematics on tubesandmore.com. You can see basic tube circuits on aikenamps.com. I looked for shematics for your organ on google, no luck. You might find other Conn organ owners on organforum.com.

[Steerpike]

My experience is limited to Lowrey, but the swell pedal controls tremelo as well, by means of it having an additional switch on the pedal itself - up/down controls swell, side-to-side controls tremelo. If you swapped over the two sensor wired you might get the effect you describe.

Such an old organ might have a lot of dirty contacts in it - with lots of stops there are so many switches in the signal path that can go wrong. And tube sockets are another source of dodgy contacts.

[Firepowerforfreedom]

Originally Posted by indianajo

Before taking the back off the organ, read the sticky thread at the top of the tube amplifier forum about tube repair safety. Tubes have lethal voltages, you have to keep your hands out when the power is on and discharge the capacitors with a tool before putting your hand in again. That said, you might try swapping the RCA plugs for a quick fix. If that doesn't work, you need an AC voltage detector, either a DMM with a 2 VAC scale or lower, or a 20 Mhz (cheap) oscilloscope with a scope probe. Both will need two clip leads for attaching the ground to the chassis and the plus to the point of investigation. Look for the output of the section that you want going to the pedal- turn it on and off, and look with the detector to make sure you have the right one. Clip the plus after the DC blocking capacitor, not right on the plate itself. Then trace the wires going to the pedal and see if it is the same one. If not, trace the wires and see why not. Obviously the pedal is connected properly on the output side to the power amp. When tracing wires, notice that the plates of tubes are the outputs, and the grids are inputs. You can see tube schematics on tubesandmore.com. You can see basic tube circuits on aikenamps.com. I looked for shematics for your organ on google, no luck. You might find other Conn organ owners on organforum.com.

Thanks for the advice. I did read the sticky thread and made sure to turn off and unplug the organ when I was switching the tubes. To make sure I didn't leave any oil from my hands on the tubes, I used some plastic gloves.

The cables for the RCA jacks are stapled to the floor of the organ, so I don't think they would have gone the other way around. I'll try removing the staples and plugging them in that way, just to see. One of the connectors looked like it was cracked on the side and didn't seem to be making good contact (hmm).

Thanks for the link to the other forum. I'll try it and see if anyone there has a 4xx series.

[indianajo]

If it is not physically possible to swap the RCA plugs, don't bother, you or previous owner didn't do it. One thing that can happen, the two different inputs can go to a tab (plastic tombstone switch) somewhere, and the tab has gotten pushed too far and the plastic has jumped over the fork on the slider and the slider is in or out too far.
Really, tracing with a scope or DMM is your best bet without a schematic. Swapping tubes can help you find a bad one if the sockets are labeled as to function or you can figure out what the function of a socket is by what doesn't work with the tube left out. Getting under the chassis is where you need te get serious about safety. You haven't said whether you have swapped out your electrolytic capacitors yet; the calender says they are all mostly bad. See my long speech about electrolytic capacitors on the electronics division of organ maintenance section of organforum.com. I just advised a Conn 720 owner to shotgun replace his electrolytic caps, and how to do it briefly. Lots of weird symptoms on my 1968 Hammond H182 went away when I shotgun replaced the electrolytic caps. I bought a spare H182, the Pro tech has replaced a couple of tubes over the years, but it still sounds thin and reedy because he didn't bother to replace the time consuming electrolytic caps. My thunderous deep sounding H182 has all origiinal tubes, and all new electrolytic caps I replaced last winter.

[Firepowerforfreedom]

Originally Posted by indianajo

If it is not physically possible to swap the RCA plugs, don't bother, you or previous owner didn't do it. One thing that can happen, the two different inputs can go to a tab (plastic tombstone switch) somewhere, and the tab has gotten pushed too far and the plastic has jumped over the fork on the slider and the slider is in or out too far.
Really, tracing with a scope or DMM is your best bet without a schematic. Swapping tubes can help you find a bad one if the sockets are labeled as to function or you can figure out what the function of a socket is by what doesn't work with the tube left out. Getting under the chassis is where you need te get serious about safety. You haven't said whether you have swapped out your electrolytic capacitors yet; the calender says they are all mostly bad. See my long speech about electrolytic capacitors on the electronics division of organ maintenance section of organforum.com. I just advised a Conn 720 owner to shotgun replace his electrolytic caps, and how to do it briefly. Lots of weird symptoms on my 1968 Hammond H182 went away when I shotgun replaced the electrolytic caps. I bought a spare H182, the Pro tech has replaced a couple of tubes over the years, but it still sounds thin and reedy because he didn't bother to replace the time consuming electrolytic caps. My thunderous deep sounding H182 has all origiinal tubes, and all new electrolytic caps I replaced last winter.

Hey, these electrolytic caps wouldn't happen to look like, say, a row of big yellow capacitors located right under the swell manual? I noticed these when I went to look in my Conn. If these are them, how do I replace them?

[indianajo]

Read this, all explained Conn 720 losing volume drastically, need help!! The most important electrolytic is the tall 4 gang one near the power rectifier tube, a 5AR4, 5Y4, 6X4 or something, near the power transformer. Read about discharging the big electrolytic caps with an insulated resistor tool, these have enough energy in them with the power cord unplugged to kill you. But defying death with knowledge and living to boast about it is kind of fun.