M101 has almost no volume without vibrato engaged

[Guest]

I am the lucky new owner of a lovely (okay, old but lovely) M101. Very glad I found this site. You all seem to be the right place for me to be.
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At first I thought I was really in a bad way, because the volume was so low I could barely hear a note, even when the expression pedal was at max volume, etc. But then I un-depresed the vibrato Off selecter -- and got good volume. What's the likely cause of getting good volume when vibrato is engaged, but almost no sound when the vibrato is not engaged? </p>

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My guess would be the tubes need replacing (not the reverb ones, but the other set on the unit on the left, when looking at it from the rear)? </p>

(by the way, i have edited this and a few other posts to correctly reflect the fact that i was talking about "reverb" and meaning "virbrato" for a while. this means that some responses no longer make sense BUT hopefully people finding this thread later will not be confused -- and in fact having changed the words to read right will help out.)
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[Guest]

Re: M101 has almost no volume without reverb engaged



Hi Nathan</p>

The reverb amplifier is almost completely separate from the main amplifier, and has its own speaker. The organ's signal must be being generated properly and going through the preamplifier as normal to get signal to, and subsequently sound from, the reverb. This is good news! The power amp. tubes (two 6L6, on the left chassis) are the only tubes in the organ to seriously suffer from wear, so one or both are most likely bad. Replace these as your first port of call.</p>

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Anthony
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[Guest]

Re: M101 has almost no volume without reverb engaged



Cool. So I could pick up a pair of these:</p>

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http://www.guitarcenter.com/Electro-Harmonix-6L6-Matched-Power-Tubes-210090-i1387411.gc</p>

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and give them a try?
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[Guest]

Re: M101 has almost no volume without reverb engaged

By the way, do I want "soft" or "hard" tubes? I know that with a guitar amp, I like the distortion of a "hard" tube that has a distorted sound without needing to be turned up too loud. But maybe with an organ, one doesn't want that?

[Guest]

Re: M101 has almost no volume without reverb engaged (woops not REVERB but VIBRATO!)



My mistake: What I meant was "VIBRATO" not "REVERB".</p>

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So, I get almost no sound when VIBRATO is cancelled.</p>

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I assume that is NOT a tubes issue? Or, if it is, it is some different tube(s).</p>

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The service manual says:</p>

</p><blockquote>

Figures 23 through 26 show only the "Virbrato" channel of the amplifier. All tones sent through this channel have the vibrato effect. The in the M-100, when the vibrato is not desired on one manual or both, the "Vibrato Cancel" tabs in the down position feed their signals through the "no Vibrato" channel of the amplifier. </p></blockquote>

This appears to be where I have a problem, if I am making the right observation right now.
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Since I have sound (very quiet) via the "no Vibrato" channel, I guess it's not a un-attached wire (or wires)?</p>

In any event, I am having trouble reading the diagrams to see where that "no Vibrato" channel is, though I can see where all the other Tablets have their input.
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[bluetantra]

Re: M101 has almost no volume without reverb engaged (woops not REVERB but VIBRATO!)

Check V2, a 6AU6; it amplifies the non-vibrato signal.

[Guest]

Re: M101 has almost no volume without reverb engaged (woops not REVERB but VIBRATO!)



Cool. Thanks. </p>

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The good news is it looks like I can buy one for $10 plus shipping, online. The bad news is that it seems far less common than some other tubes, which I could pick up at my local Guitar Center. </p>

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The guy that sold me the organ has a tube tester -- but he was a bit of a character, and whether he shows back up with the tester at any time is tough to say[:)] so short of finding another local person with a tester, it might be worth the investment since that is likely the problem (and new tubes are seldom a bad idea).
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[Guest]

Re: M101 has almost no volume without reverb engaged (woops not REVERB but VIBRATO!)



Here is what the guts look like. I seem to recall seeing a picture online that labels every tube. There is a tiny one in the service manual, but I need to blow it up later to make sure I know which is which. But I post the picture largely because I now realize (after taking the photo) that they appear to be the original tubes from 1960 or whenever.... so that makes me think, even more, they might be the culprit.</p>

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Those are the main amp. I think the V2 is one of those if I recall the key I found on line the other day.</p>

Just for chuckles, here is what the vibrato control unit looks like:</p>

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[Guest]

Re: M101 has almost no volume without reverb engaged (woops not REVERB but VIBRATO!)



The reverb amp looks similarly "original" in the sense of there being Hammond tubes there, too:</p>


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[Guest]

Re: M101 has almost no volume without reverb engaged (woops not REVERB but VIBRATO!)



Anyone buy one of these sets from this guy?</p>

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http://cgi.ebay.com/Hammond-Organ-Co...742.m153.l1262
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[Guest]

Re: M101 has almost no volume without reverb engaged (woops not REVERB but VIBRATO!)



Looks like he is mentioned elsewhere on this site as reputable. And I exchanged some email with him and he does do tube matching for the pairs, and guarantee satisfaction.</p>

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So now I just need to figure out what reverb unit I have. Can anyone tell from the photo I posted, above? I cleaned off the two large sqaure flat units thinking one might have a label, but no dice.</p>

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Or can I tell from the serial number?
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[geoelectro]

Re: M101 has almost no volume without reverb engaged (woops not REVERB but VIBRATO!)



Nathan, there are two 6AU6 tubes on the main chassis. There are three tubes with can coverings. The center one and the one on the right are the two 6AU6's. You can swap them with each other. Then check to see if your symptoms change. If so, one of the tubes is bad. If not, you have a problem under the chassis. Likely a bad screen grid resistor on the non-vibrato channel.</p>

George
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[Guest]

Re: M101 has almost no volume without reverb engaged (woops not REVERB but VIBRATO!)



Cool. Just to make sure I understand: It is these two that are circled in this photo, right?</p>


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[Guest]

Re: M101 has almost no volume without reverb engaged (woops not REVERB but VIBRATO!)



What luck! I was able to find a neighbor whose father was a TV repairman back in the early 60s and she still had his old tube tester!</p>

So I ran all the tubes through the tester. Whew! It's a wonder I got any sound at all from this thing! I thought maybe one or two or three tubes would be weak or dead -- like the one for the non-vibrato channel.</p>

Well, the non-vibrato channel tube WAS very much in the weak part of the range (ie, far into what the tester called "replace"). What I didn't expect that the other (vibrato) channel tube was one of the few that tested as "good" (green on the dial).</p>

one 6AU6 was bad (the non vibrato channel)</p>

one 6AU6 was good (vibrato channel)</p>

two 12 AU7 were bad (i didn't trace the role of any other tubes)</p>

two 6C4 were good</p>

one 12AX7 was bad (and not an original hammond-labeled tube)</p>

one 6V6 tested good</p>

one 6V6 tested "shorts" but also "good" on the standard test</p>

one 6BA6 tested very good (and was not a hammond tube but a sylvania; perhaps a prior owners replacement)</p>

one 5U4 tested good (though the "life" test indicated it was not long for this world) </p>

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and then on the reverb amp:</p>

one 12AX7 tested as "shorts"</p>

one 12AX7 tested as bad
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one 5Y3 didn't produce any reading (but the housing was loose so perhaps no longer a VACUUM tube at all</p>

and the two 6BQ5 were not testable with the equipment I had (or at least they were not listed with a HEAT and SENSITICITY rating so I didn't have a basis for testing nor know which socket to use) </p>

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At this point I am truly shocked I was getting sound at all -- though the tubes that tested "bad" were of course working a little, I guess.</p>

Sounds like replacing them all is the way to do. Off to ebay....
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[Guest]

Re: M101 has almost no volume without reverb engaged (woops not REVERB but VIBRATO!)

[quote user="geoelectro"]

Nathan, there are two 6AU6 tubes on the main chassis. There are three tubes with can coverings. The center one and the one on the right are the two 6AU6's. You can swap them with each other. Then check to see if your symptoms change. If so, one of the tubes is bad. If not, you have a problem under the chassis. Likely a bad screen grid resistor on the non-vibrato channel.</p>

George
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I replaced the tubes and I think I may have killed a good tube putting it into the V2 (fifth from the right) spot.... so now I gotta ask:</p>

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"Likely a bad screen grid resistor on the non-vibrato channel."</p>

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Can you point me to an online guide to how one tests a resistor? I have volt-meter, but if that's not the right tool I am open to buying what it is that I need.
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