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Jensen U20 in 31H Leslie

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  • Jensen U20 in 31H Leslie

    I was gifted a Leslie 31H with series III amp. It is the only 31 I've put my eyes on. I'm guessing it's mid vintage: looks like a later style serial plate and side-mounted motor speed toggle switch (did they all have that?). Original woofer has been removed (I plan to get a F15LL field coil woofer for it). Jensen U20 treble driver. I am unfamiliar with this and am not finding info online. Anyone familiar with the U20? Did the 31H later have a V21 and how do they 2 compare? Thanks for any assistance.

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    David McCracken

  • #2
    Hi Dave,

    I've worked on a number of 31Hs. 31H cabinets SN 8000 and higher had 32H amps. I believe they all still had the toggle switch on the side.

    As far as I know, the Jensen U20 was used in some earlier Leslies, but may not be original to this cabinet. The driver may be older than the cabinet. Sal would have known, and there is probably something by him about this in the Hamtech archives. I've seen older 31Hs that had V21 horn drivers in them.
    I'm David. 'Dave' is someone else's name.

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    • #3
      Hi Dave and David.

      Yes, all 31 series Leslies had a single switch on the cabinet starting with the 31A. The 30A’s had two switches for separate top and bottom rotor switching.

      Except for the very early Units, 30A’s used the Jensen UF20 FC driver. When production began after the war, the 31A used the U20 PM driver. I have a couple of 31’s Series 3 and if I recall, the V20 preceded the V21. I’ll check when I get a chance.

      Mark

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      • #4
        I have two 31Hs and a 31A, and all of them have a driver that looks similar to that one, and not a V21. I haven't taken it out and confirmed, though. I think the U20 might be a bit brighter - my mentor was saying that one of his Leslies, a 147, has an old treble driver. The way he described it, it sounded like one of these, and definitely not a V21 (he is familiar with what those look like). That Leslie has a LOT of treble response, bordering on harsh, but still a great tone. All my tall cabinets sound great and well-balanced, so it could be that specific driver or the way it was interacting with the 147's electronics.

        I was under the impression that the last 31Hs did not have the switch in the cabinet. The 32H series III amp has no place for that switch to control a motor socket like the series 2 and earlier wide-body amps, right? My 31Hs have the switch (with the earlier amps), and in fact the 31A has a series 3 amp - whoever installed that removed the switch (it just has a hole in the cabinet). I seem to remember reading that while Leslie stopped officially offering the 31H at some point in the 50s, they were still available by custom order into the 60s.

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        • #5
          Originally posted by snacks View Post
          I seem to remember reading that while Leslie stopped officially offering the 31H at some point in the 50s, they were still available by custom order into the 60s.
          What I was told is that 31H cabinets were officially out of production in the mid-50s, but could be special-ordered through 1958. At that point, Jensen had ceased production of the field-coil woofers, and Leslie had redesigned their amps with 6550s. I've seen a number of 32H amps, but none with component production dates after 1957. If Leslie was building 31H cabinets later than that, they would have been using legacy components.
          I'm David. 'Dave' is someone else's name.

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          • #6
            I have a 31H that is very late production. 9200 series serial number. I've dated it to '58. It still has the switch and the newer amp with double 6sn7's and grey hammered finish.
            It has a V21 but it's not original to the unit unfortunately.
            Hammond B3 (55), B3 (70), B3 (72), B2 (51) conversion, A100 (61) chop, A100 (62), A105 (75), Northern BC (39) empty.
            Pile of Leslies of various flavours, Minimoog, ARP Odyssey, MaxiKorg, Hohner D6, Rhodes 54, Rhodes 73, Wurlitzer A200, Wurlitzer A203W

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            • #7
              Originally posted by nonreverb View Post
              I have a 31H that is very late production. 9200 series serial number. I've dated it to '58. It still has the switch and the newer amp with double 6sn7's and grey hammered finish.
              It has a V21 but it's not original to the unit unfortunately.
              What I've seen in most 31Hs is a V21 with a bell-end cover on the back, which makes them look different even though they're the same horn driver. I also have a 32H amp with two 6SN7s from '57. And I think most of the tube sockets are micanol rather than the earlier phenolic wafer.
              I'm David. 'Dave' is someone else's name.

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              • #8
                Originally posted by David Anderson View Post
                What I've seen in most 31Hs is a V21 with a bell-end cover on the back, which makes them look different even though they're the same horn driver. I also have a 32H amp with two 6SN7s from '57. And I think most of the tube sockets are micanol rather than the earlier phenolic wafer.

                I was hoping when I got it that it would be all original....considering they're as rare as hen's teeth up here. Alas the V21 is from the '60's. No bell cover. Here's a pic of the amp.
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                Hammond B3 (55), B3 (70), B3 (72), B2 (51) conversion, A100 (61) chop, A100 (62), A105 (75), Northern BC (39) empty.
                Pile of Leslies of various flavours, Minimoog, ARP Odyssey, MaxiKorg, Hohner D6, Rhodes 54, Rhodes 73, Wurlitzer A200, Wurlitzer A203W

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                • #9
                  I have a 31 -h with just about as nice sounding as they get, it has a series 3 amp, does not have a switch and never did, also has a v-21 and has never been out of the cabinet. I have had several of these cabinets and they all seem to sound a bit different. this one very mellow. love it .

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                  • #10
                    I thought there was a V20 in the mix, V21 after that? No facts just memory?
                    1956 M3, 51 Leslie Young Chang spinet, Korg Krome and Kronos

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                    • #11
                      Originally posted by Baldwin51 View Post
                      I have a 31 -h with just about as nice sounding as they get, it has a series 3 amp, does not have a switch and never did, also has a v-21 and has never been out of the cabinet. I have had several of these cabinets and they all seem to sound a bit different. this one very mellow. love it .
                      There is a V-21 sound, but . . . no two V-21 horn drivers sound exactly alike, especially after all these years. It's my impression that they were never that consistent a product, even when brand new. In many other horn drivers, the diaphragms are very precisely made with alignment pins. Not V-21s. The V-21 was not part of Jensen's High Fidelity line, as far as I can tell from the catalogs I've seen. I think it was mainly for use in public address systems. As such, "tone" was not their main goal.
                      I'm David. 'Dave' is someone else's name.

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                      • #12
                        I think the V-20 was before the V-21, I just discovered that my 21-h has a v-20 , I have never had a problem with the sound very nice,, both my 31 and 21 have the same amps series 3 with 5881 out put tubes. no switch on outside of 31-h . I don't know what the difference is in the V-20 and the V-21, outside appearance is the same and I am told by a expert that the diapram is the same, so I cant figure it out. the 31 is not as bright sounding as the 21 but it has a .003 cap across the plates of the 67n7 tubes which dampens the highs a bit. interesting.

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                        • #13
                          U-201

                          While disassembling an old Leslie tallboy for restoration, I came across a Jensen model U-201 (not U-20). The first thing unusual was the red paint around the inside top of the driver (see pic #3). Also, the body color is a drab green instead of the standard silver.

                          Once I saw the side of the driver, it made sense. It was made 5 months before the end of WWII and was probably never intended for a Leslie. I think the first word is supposed to be ‘Fungus’ not ‘Fungs’ (see pic #4). Forgot to measure the VC.

                          Body color drab green/gray
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                          U-201 Tag
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                          Red ring around oily spindle plate
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                          Stencil - ‘Fungs Treatment Applied 4/18/45’
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                          Last edited by markm; 05-01-2018, 08:11 PM.

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                          • #14
                            Originally posted by markm View Post
                            Forgot to measure the VC.
                            The VC measured just over 12Ω. I removed the spindle plate and took a few more pics.


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                            • #15
                              Am I the only one wondering what in the world "fungs treatment" means?

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