M101 Reverb Problem

[Guest]

Elsewhere I asked about reverb when I really meant vibrato. This is not that situation. I do really mean reverb this time! Here is what I am looking at:</p>

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I replaced all the tubes on my reverb amp in my M101. They were, many of them, dead previously. But the new tubes didn't solve my problem.</p>

I removed the spring tank, and tried shaking the spring when the reverb amp was engaged (via the switches above the keyboard) and the good news is that the springs were loud and clear via the reverb amp and the speaker!</p>

So I figured there was a problem with the sound getting INTO the spring tank.</p>

Sure enough, I opened it up, and found a dangling wire that appears to need to be connected to the input RCA plug/jack:</p>

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So I soldered that to what looked like the right place on the jack... and connected the tank to the output on the reverb unit (ie, where the rca that goes from the reverb unit to the tank connects to the reverb unit) via the exiting RCA cable. No dice. </p>

I decided maybe some new wire and a new RCA plug would help. It did, but only when I was hold the wires to the output of the reverb unit AND holding the wires in the spring tank so that the exposed one touches the case of the tank. And things worked even better when I ran a lead from the main speaker, down to the input of the spring tank. In fact, it sounded real loud and full of reverb, then.</p>

I guess the good news is that the reverb amp appears to be okay, and the spring tank is not in horrible shape. But I cannot quite put my finger on how to solve things. </p>

In one sense, I could run wires from one of the speakers down to the input on the spring tank, and call it a day, but while I have been told that it is indeed the speaker level output that gets used as the reverb input, it really seems like there is a special level coming out of the reverb unit and going into the spring tank, and that's how it is supposed to run.</p>

Any recommendations for what else to troubleshoot or try?
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[Model E & Me]

Re: M101 Reverb Problem

[quote user="nathan_h"]


In one sense, I could run wires from one of the speakers down to the input on the spring tank, and call it a day, but while I have been told that it is indeed the speaker level output that gets used as the reverb input, it really seems like there is a special level coming out of the reverb unit and going into the spring tank, and that's how it is supposed to run.</P>


Any recommendations for what else to troubleshoot or try?
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<P mce_keep="true">[/quote]</P>
<P mce_keep="true">Visit the Captain Foldback website for diagrams of the M-100 series reverb units. There should be a pair of leads from the speaker to the reverb amplifier. Basically, all that happens in the reverb amplifier is that the signal from the speaker leads passes through a volume limiter on its way to the reverb unit. This limiter is just to prevent overloading the reverb unit at very high volume levels. At normal volume, whatever that means, it has very little effect. </P>
<P mce_keep="true">The volume limiter includesnon-linear resistances in the form of miniature light bulbs - I think they are type 12. Some designs use one bulb,later ones use two.It is very possible that the filaments are open in these bulbs, which would prevent the signal from getting to the reverb unit. They are located in the reverb amplifier -you'll have to turn it upside down to see them as I recall. </P>
<P mce_keep="true">If the bulbs are gone, replacements arenot easyto come by and expensive. They are rated 6.3 volts, 0.15 ampere, which is the same as the very common #47 bulbthat has a bayonet base. Now that you have developed some proficiency with a soldering iron, you could solder a couple of bayonet sockets in place of the #12 bulbs and use #47s instead. Both sockets and #47 bulbs are commonly available at Radio Shack.</P>
<P mce_keep="true">Or just leave the leads from the speaker directly to the reverb unit. As long as you don't get unacceptable (to you) distortion from the reverb unit at the loudest levels you play, there is nothing wrong with leaving it that way.</P>

[Guest]

Re: M101 Reverb Problem

Or just leave the leads from the speaker directly to the reverb unit.

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This sounds like it might be a good option. But can you clarify where on the reverb unit I should connect the speaker to? That is, in doing my testing, I was holding the leads on the speaker terminals of one of the big speakers (ie, NOT the reverb speaker, of course) and the other leads were connect INSIDE the spring tank. If that is acceptable, I am good to go. I don't really need the variable attenuation of the bulb under the reverb amp.</p>

But now that you describe that bulb, I'm guessing it is still there, since when the leads went directly from the speaker to the tank, the volume produced was significantly louder than when I did it "the right way" and used the little output on the reverb amp (called "driver").</p>

I assume this is the key wiring diagram from the Capt Foldback site?</p>


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A few more details after a bit more troubleshooting:</p>

Elsewhere, bluetantra wrote:

"The audio signal comes from the top side of the main amplifier (the larger of the two chassis) in a small round plug with 4 wires: brown and black usually, which are to the console pilot light (at line voltage), and green and black, which are the audio signal to the main speakers and reverb amp. The reverb amp is fed the audio signal by a wire (probably red) from one of the main speakers. " </p>

I traced all these lines VISUALLY and could not find one that appeared disconnected. For example, here is what they look like at the reverb amp:</p>

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and details</p>

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[Guest]

Re: M101 Reverb Problem



Honestly I think the key issue may be the wiring in the spring tank itself.</p>

See this is the "right side" (if one is behind the organ looking into the organ and the tank is mounted in the right way). It is the output, back to the reverb amp. (It looks like it is the left side because I have removed the tank and turned it upside down to work on it.)</p>

This looks like the original wiring and mounting of the RCA jack:</p>

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Now, for comparision, here is the input side. Notice how the RCA plug has had a screw added where there was a grommet like device on the other side holding it? And notice how the neutral wire is not a nice cloth-covered wire anymore but some bare silliness?</p>

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I'm wondering whether this was serviced at some point, and it wasn't done well, and now I am having this trouble because of that.</p>

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I'll admit I have NOT removed the amp and looked at the light underneath to see that it is there and working. I *do* get a signal at times via the "driver" output of the amp (which is where it is supposed to come from -- though it is quiet) and louder signal from the speaker terminals. But I have to fuss with this funky neutral wire, and hold it against the side/case of the spring tank.
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[Guest]

Re: M101 Reverb Problem



But maybe I should pick up this lamp, just in case. Is the A035 reverb amp (or the same bulb as used in an A035 reverb amp) used is "later model Hammonds", which is all the site says by way to describing what this lamp is for?</p>


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http://www.tonewheelgeneral.com/build_page.php?category=Hammond+Organ+Parts&amp;su bcat=Accessories&amp;offset=12&amp;searchterm=&amp ;searchtype=category</p>

Looks like a number 12 lamp is also used in the A044 and the A066, which is a "much later" model reverb amp than mine (A035). So I'd be hopeful that this lamp is the right one.
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[Guest]

Re: M101 Reverb Problem



Update: Got a message back about that lamp:</p>

"Yes, that is part number LAMP, a 6.3 VAC unit. Also used as the pilot
amp in the tonewheel organs."
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[Model E & Me]

Re: M101 Reverb Problem



You will notice that on theschematic diagram there is a connection between the Console Ground and the Amplifier Ground at the "GND" terminal on the reverb amplifier. I was not able to see that on your photos, but you do need to make sure the two chassis are tied together, as that is the signal return path.</P>


You will also notice on the schematic diagram that there are either resistors or the lamp in series with the signal from the main speaker (at the SIGNAL INPUT terminals)and the reverb driver coils (at the DRIVER terminals), and that the reverb driver coils are not connected to ground on eitherside. This is because one side of the main speaker signal is grounded, and so if the reverb driver coils were also grounded, part of the volume limiter would be shorted out. You report that when you ground one side of the reverb driver coils you get some signal.Since that effectively shorts out part of the volume limiter, it would again seem to point out that the volume limiter may be the culprit.</P>


Things I would do (an ohmmeter would help here immensely):</P>


Verify that the reverb amplifier chassis and the main amplifier chassis are electrically tied together.</P>


Verify that one terminal of the main speaker is grounded to the main amplifier chassis</P>


With the reverb tank disconnected, verify that there is electrical continuity between each of the SIGNAL INPUT terminals and the DRIVER terminals on the reverb amplifier. These should be low, but not zero, resistance</P>


On the reverb tank, verify that neither input jack terminal is connected to the tank</P>

[Guest]

Re: M101 Reverb Problem



Thanks for the detailed note. I probably won't be able to dig in again for a couple of days, but this will be a great recipe to follow at that time. I'll report back.</p>

In the interim, here is another data point or two.</p>

When I connect the leads from the speaker terminals OR from the driver terminals on the amp, like the following photo shows inside the tank, I get lovely reverb. (Too much when going direct from the speaker terminals, but just about right when coming from the driver output on the reverb unit.)</p>

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However, when I do it via this connection in the reverb tank, I lose it. Shouldn't the signal be going down the wire in the photo above, so that when I connect it like this photo below, I would still have a signal? (Or does this further bolster what you are suggesting for troubleshooting?)</p>


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[Model E & Me]

Re: M101 Reverb Problem

[quote user="nathan_h"]


Thanks for the detailed note. I probably won't be able to dig in again for a couple of days, but this will be a great recipe to follow at that time. I'll report back.</P>


In the interim, here is another data point or two.</P>


When I connect the leads from the speaker terminals OR from the driver terminals on the amp, like the following photo shows inside the tank, I get lovely reverb. (Too much when going direct from the speaker terminals, but just about right when coming from the driver output on the reverb unit.)</P>


However, when I do it via this connection in the reverb tank, I lose it. Shouldn't the signal be going down the wire in the photo above, so that when I connect it like this photo below, I would still have a signal? (Or does this further bolster what you are suggesting for troubleshooting?)</P>


[/quote] </P>


Your reasoning is correct but it is difficult to see exactly where the test leads are connected.</P>


In the first picture. If the test leads are coming fron the DRIVER terminals on the reverb amp and the "bare" wire from the input jack to the driver coil is not brushing against the (grounded) frame of the reverb coils and it works all right, that would say that everything in the reverb amplifier is wired and working correctly.All that is leftis either the wires from the DRIVER terminals to the reverb unit, or the RCA plug itself, or the input jack itself. </P>


In the second picture, it can't be seen whether the red insulated alligator clip is holding the "bare" wire away from the frame of the reverb coils or whether what looks to be the enamel covering on the wire (hence "bare" in quotes) is scraped away under the clip so that there is a good electrical connection.</P>

[Guest]

Re: M101 Reverb Problem



Replacing the RCA socket did the job. Old:</p>

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New:</p>

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Okay, it's pretty ugly, but it works and I'll find a proper RCA jack to put in there at some point.</p>

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I still think I'll pick up a couple of those lamps and probably throw a few tubs into my shopping cart, as well, as spares.
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