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M-100 amp has very low output

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  • M-100 amp has very low output

    Hi all.

    I just picked up very clean but long neglected M-100 and JR-20 cab. Generator was frozen but the organ was otherwise very clean. Naptha/WD-40 and hammond oil have it spinning long and quiet now. Everything seems to work as it should electronically except that the main organ output is very low. Reverb side is way louder despite the fact it isn one speaker and a smaller amp. Both 60 and 120 hum seem pretty quiet. I'm obviously gonna check the tubes but I am thinking some of the signal coupling caps may be off. FWIW the bass pedals are pretty darn loud for a m-100. Significance?

    cheers

    B

  • #2
    Is the problem present both with vibrato on and off?
    Current organs: AV, M-3, A-100
    Current Leslies: 22H, 122, 770

    Comment


    • #3
      Slightly louder with vibrato on. Not huge. Tested the 6v6's and they are pretty tired. Gonna get out the tube tester tonight and test the rest.

      B

      Comment


      • #4
        A little louder is normal with vib channel.
        Lots of pedal volume,normally almost JR20 levels from M100?
        If so the 6V6's are still operating normal even if tired.
        6AU6 pair are the vib/non vib channel tubes.Swap them and check.
        Resistors and caps off these should be checked.

        Schemos and diagrams are online free for the M series.
        They weren't free back when I really needed one.
        Before the internet service manuals and the local Hammond tech
        was how things got done.
        No tech available? Better read those old documents.
        The troubleshooting guide in every manual is a must read IMO.
        A100/251 A100/147 A102/222 B2/142 BV/147 BCV/145 M3/145 M102/145 M111/770 L101/760 T222/HL722 M111/770 no B3/C3!

        Comment


        • #5
          briguy1960 Grab the manual here. It's worth getting it printed nicely, and bound. https://archive.org/details/HammondO...delsMM2M3M-100
          Unwanted Bitcoin? Dispose of them safely here:14hjbheQVki8eG75otRK4d2MQBarCCWQfJ

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          • #6
            In an M-100, the reverb amp gets its input from the main amp output (after going through a compressor/limiter made from a few resistors and light bulbs). If the reverb amp is producing its expected level of output, then the main amp must also be producing its full output. That suggests the amp is working, and the main speakers themselves are suspect.
            Stefan Vorkoetter: http://www.stefanv.com

            1962 Hammond M-111 with Improved Vibrato, Internal Rotary Speaker, Drum Machine,
            Window Seat Tone Cabinets, Completely Rebuilt Amplifier, and Recapped Tone Generator.
            1978 PAiA 1550 Stringz'n'Thingz with many enhancements.
            2017 Raspberry Pi organ-top synthesizer.

            Comment


            • #7
              Interesting thread! I just rescued a '63 M100 a few days ago. I recapped the TG which improved the sound noticeably, but interestingly my '55 M3 sitting next to it is quite a bit louder. I haven't started probing the thing in depth yet but a quick check of the actual speaker voltages with a meter shows the M3 making more sound with ~6 db less voltage than the M100. Hmm...
              Tom in Tulsa

              Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720

              Comment


              • #8
                Just to be clear I'm only working on the M-100 for now. The seller threw in the JR-20 but I'm not sure the two were ever hooked up together. Both look like they have only been in homes and the woman admitted she had not fired up the organ in 8 years. As I near retirement, one of my projects is to getting into understanding tube electronics. Everyone needs a hobby right? I've got a couple of good multimeters, signal generators ,two scopes and a variac, and soon ....time. There is a lot of 120hz coming out of the reverb amp so I might start with that one first. It looks like a multi cap cap can. Does anyone know if it is hard soldered in or will it pull out like on a leslie 147?

                On the Jr-20, it seems there is no oil in the tubes. What kind of oil? how much to put in. What a beast of an amp chassis !

                Thanks everyone!

                Brian

                Comment


                • #9
                  Can caps in Hammonds are always soldered.
                  Current organs: AV, M-3, A-100
                  Current Leslies: 22H, 122, 770

                  Comment


                  • #10
                    Originally posted by briguy1960 View Post
                    Just to be clear I'm only working on the M-100 for now. The seller threw in the JR-20 but I'm not sure the two were ever hooked up together. Both look like they have only been in homes and the woman admitted she had not fired up the organ in 8 years. As I near retirement, one of my projects is to getting into understanding tube electronics. Everyone needs a hobby right? I've got a couple of good multimeters, signal generators ,two scopes and a variac, and soon ....time. There is a lot of 120hz coming out of the reverb amp so I might start with that one first. It looks like a multi cap cap can. Does anyone know if it is hard soldered in or will it pull out like on a leslie 147?

                    On the Jr-20, it seems there is no oil in the tubes. What kind of oil? how much to put in. What a beast of an amp chassis !

                    Thanks everyone!

                    Brian
                    Hello,

                    I think there is something wrong in the speaker connerctor J1 > P1
                    May be an open ground near the 2 100 Ohms resistors.

                    Output schematic

                    Click image for larger version

Name:	M100_Output.jpg
Views:	1
Size:	98.5 KB
ID:	606622

                    JP

                    Comment


                    • #11
                      Duplicate post
                      Last edited by Jyvoipabo; 11-03-2018, 01:36 AM. Reason: Yes

                      Comment


                      • #12
                        Originally posted by Jyvoipabo View Post
                        I think there is something wrong in the speaker connerctor J1 > P1
                        May be an open ground near the 2 100 Ohms resistors
                        If that were the case, he wouldn't be getting much of a reverb output either, since, as you can see from the same schematic, the reverb amplifier's input comes from the connection to the speakers.
                        Stefan Vorkoetter: http://www.stefanv.com

                        1962 Hammond M-111 with Improved Vibrato, Internal Rotary Speaker, Drum Machine,
                        Window Seat Tone Cabinets, Completely Rebuilt Amplifier, and Recapped Tone Generator.
                        1978 PAiA 1550 Stringz'n'Thingz with many enhancements.
                        2017 Raspberry Pi organ-top synthesizer.

                        Comment


                        • #13
                          The speakers must be fine as the bass pedal output is really loud as is the percussion tones. I think the issue lies with the part of the AO-29 that is amplifying the signal from the manuals. The balance between the vibrato and non vibrato seems normal so it is further down the chain. Otherwise the organ is working really nicely.

                          Comment


                          • #14
                            No, that doesn't make sense. The vibrato/non vibrato/percussion/pedal channels all merge at the same point; so if the pedals sound fine the "down the chain" portion of the amp is fine.

                            The pedal tones have an own signal path on the M-100, which doesn't pass the matching transformer. Neither does the percussion tone, it's taken from the primary of the matching transformer. See where I'm going with this? Check the ground connections to the matching transformer. If that doesn't help, try a replacement transformer.

                            *edit* - you should have mentioned percussion earlier, that would have saved a lot of guesswork ;)
                            Current organs: AV, M-3, A-100
                            Current Leslies: 22H, 122, 770

                            Comment


                            • #15
                              Ah yes , looking at the block diagram and the schematic , your point makes total sense. To check the ground from the transformer is it sufficient to measure from the external case or do I need to take that off? Am I correct in reading the schematic that both the vib and non vibrato come from the matching transformer to the 6AU6 tubes before going to the intermediate amplifier? I think my volume issues lie before that intermediate amplifier.

                              I did a couple of simple output power tests. Hooking up a voltmeter to the main speaker outs, and with the top manual drawbars all fully pulled, I played a 1-3-5-8 f major chord at the lowest octave. With the expression pedal fully depressed the VM shows 3.3 volts output to the speakers and yes I have trimmed the air cap adjusted for max volume. Playing a low C with the pedal fully pulled out generates about 8 volts at the speaker and hooking up an electric guitar at the RCA input generates about 2.5 volts with hard strumming. However, hooked up with and O/D pedal I can easily get 12 volts and a lot of volume so obviously the output stage is working fine. One other observation is with just the first 4 drawbars pulled out (the ones that go all the way to the highest keyboard note, the sound definitely gets quieter in the highest octave. Both the 6AU6's test well with my Precision 612 tester. Good but not awesome at around 70 percent life. UPDATE I pulled out the matching transformer and made sure all the connections were snug. It does seem a little louder. The other thing I have done is a bit of tube rolling, picking the best tubes in my arsenal. Overall the organ is sounding better but certainly there is no growl like I can get on my A-100. I'm thinking replacing the resistors and caps related to the 2 6au6's might be where to go. Does anyone know what kind of AC voltages I should be seeing coming out of the matching transformer with all Drawbars pulled and playing a full chord? Thanks everyone for all the input. I'm learning as I'm going and much of the credit goes to the members of this group.

                              Retirement looms and I need to stay active.

                              Brian

                              Originally posted by enor View Post
                              No, that doesn't make sense. The vibrato/non vibrato/percussion/pedal channels all merge at the same point; so if the pedals sound fine the "down the chain" portion of the amp is fine.

                              The pedal tones have an own signal path on the M-100, which doesn't pass the matching transformer. Neither does the percussion tone, it's taken from the primary of the matching transformer. See where I'm going with this? Check the ground connections to the matching transformer. If that doesn't help, try a replacement transformer.

                              *edit* - you should have mentioned percussion earlier, that would have saved a lot of guesswork ;)

                              Comment

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