Readable Leslie 122RV Schematic

[patlaw]

Does anyone have a READABLE Leslie 122RV schematic? One original version was a fold-out labeled "SCHEMATIC: 117V TYPE 122 ROTOR AND REVERB AMPLIFIERS". I've pieced that together, but after all these years, there ought to be a pristine version somewhere. The correct schematic has the Reverb Power Supply, Reverb Schematic, Power Supply, Amplifier, and Dividing Network on a single 8-1/2 x 11 or, better yet, an 11 x 17 sheet.

[Jazz P Bass]

Try thr 122VB: http://theatreorgans.com/hammond/faq...cs/122vb-a.pdf

[patlaw]

Awesome! Thanks!

[patlaw]

I have a 122 Reverb Amp shooting fire. The FWB rectifiers are good as is hte bias supply. I cannot see the problem where the arc occur, but I do see diodes with soot all over them. They've been near the problem.

I just got it back tonight, so I'll spend a few days learning it in my spare time. It's simple enough circuit.

What I would like to find is several of the large pin/small pin connectors that are used to connect to external speakers. I want to build a test jig as I could end up repairing quite a few of these.

One design note. Is the RCA plug for the reverb tank input actually made from zip cord. Shouldn't it be shielded cable? This one may decide it was a shielded cable. And what are the two #19 blubs in series with the reverb spring? What do they do, and where can you get them?

Thanks.

The plugs are available for $14,00 each, but that's a lot.



EDIT: I found them for $8 each.

[Jazz P Bass]

One design note. Is the RCA plug for the reverb tank input actually made from zip cord. Shouldn't it be shielded cable? This one may decide it was a shielded cable. And what are the two #19 blubs in series with the reverb spring? What do they do, and where can you get them?

If you look at the schematic you will see that the Reverb Return is a shielded wire.

The lamps are used as an input circuit volume 'limiter'.

Hammond Reverb Lamp - Hammond Organ Parts - Bulbs - Hammond Reverb Lamp - CLASSIC HAMMONDS

[Enzo]

The input to the reverb pan is low impedance and is meant to be driven by the main amp speaker output. So shielding it would do nothing.
as Jazz said, the lamps are there to reduce the level of signal actually reaching the reverb pan drive coil.

The output coil from the pan is a shielded wire.

[patlaw]

The lamps are used as an input circuit volume 'limiter'.

But what do they really do? Are they a fail safe mechanism? Do they increase in resistance when they get warm? Asked another way, what happens if they're shorted? Luckily I don't have a problem with them, and I just ordered a ten pack for a lifetime supply, but I'd be curious what the symptom would be if one shorted. (If one opened, the reverb amp would be dead.)

I just finished recapping most of the reverb amp in the 122R. There are some caps on the tube board, which I have not removed yet. There was a bad coupling cap that is now replaced. There is still a level of white noise that originates before the volume pot. It may be a normal amount of hiss. I don't have a known working amp to compare it with, and the Leslie is not here for me to install it and test it.

[Enzo]

I am having a hard time imagining how those lamps could "short". The only way to short internally is to have something touching both posts. And the only thing in there is the filament. If the filament were to break free and lodge touching both, it would be, well, just like the bulb.

yes, bulbs get higher in resistance as they get hot, but I don't think they will get lit up much. I think those are #19 lamps, but whatever they are, they are 6.3v 0.15A filaments. That works out to 42 ohms hot. 84 ohms the both of them in series. I don't know the pan input resistance, but if we look at the 15 ohm resistor across it, and in series with the lamps, that totals about 100 ohms. Or about 15% of the total, Meaning that whatever output from the main amp that is used as drive will only be at 15% at the reverb pan. What is the output power of the main amp?

The bulb is just a resistance. yes, a potentially variable one, but mainly it attenuates the signal to the pan.

[patlaw]

I don't know how one could short either, but I do understand if one opens. So do you think they're being used as high wattage resistors at their cold value?

One of the pin sockets is not holding well, and my efforts to tighten it have not been successful. It's at the point that if I keep messing with it, I'm going to break it. I wonder where I'd find replacement pins.

[g1]

Bulb limiters can act as dynamic resistors. The more current, the more heat; the more heat, the more the resistance goes up.
They are often used in PA cabinets as horn protection. They limit the peaks, but will also burn out and offer "fuse" protection if pushed too hard.
In this case, they may be trying to protect the tank input transducer, or may just be trying to prevent harsh sounding peaks.
As you mentioned, if the bulb opens, the circuit quits working. However if one is shorted, it just bypasses the limiter effect.

[Enzo]

I don't know why one couldn't change the socket and use a different based bulb with same voltage and current ratings.

However, if your female pins won't tighten, I think my first trick would be to grab a couple female molex pins from my drawer and fashion a connection. 06 size.

[patlaw]

I finally got it to tighten enough that it should be ok. The sockets look like they might have come out of an octal socket.

I did finally dig into the tube printed circuit board. It had two electrolytic caps on it. One was toast. The other seemed fine. Of course, I replaced both of them.

At this point, I'm about ready to pronounce it as "fixed". The problem is I don't have anything to compare it with. It has plenty of gain, and strangely enough, the voltages on the schematic actually match the voltages in the circuit. It is amazing how close they are.

My function generator is an OLD Southwest Technical Products home brew. The output level control does not take the output down all the way, so I cracked it open. One of its power supply caps was bubbled on one end, but it checked okay on the capacitor meter. (I don't have a way to measure ESR, but it has to be high.)

I've been out of the repair mode so long that I have to repair my test equipment before I repair the equipment I need to repair!