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Westbury "The Tube" distortion pedal transformer

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  • Westbury "The Tube" distortion pedal transformer

    The Free Information Society - Westbury W20 Electronic Circuit Schematic

    I have the Nady version of this pedal and I want to make some changes, but I don't want to modify this one. I'll build a new one instead. But I need some transformer advice.

    The transformer in the pedal is pretty small. It measures 1.5" square. I don't know much about transformers. Where can I get one this small? What would I ask for?

    Thanks, guys.

  • #2
    As shown on the schematic: 6.3V 300 mA or more, center tapped; 200V 10 mA or more.
    Anyway I don't understand very well why would anybody prefer it over other pedals, since the distortion comes from a pair of diodes, like on countless pedals.
    Juan Manuel Fahey

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    • #3
      Damned if I know, JMF. Must be something about the diodes in the feedback loop. It just sounds better and more natural (to me) than the SS pedals I've tried. I do hear that tube in there, and the diode effect is somewhat moderated somehow.

      edit: That said, it does need some tweaking, IMO. I want to beef up the bottom a bit (larger coupling caps) and cut the treble (tone circuit). I currently have to use an eq between it and the amp.

      Thanks for the info. Got any recommended brands or dealers? I don't know where to get one even. Sheesh!
      Last edited by Boy Howdy; 03-15-2010, 06:36 PM.

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      • #4
        Originally posted by J M Fahey View Post
        I don't understand very well why would anybody prefer it over other pedals, since the distortion comes from a pair of diodes, like on countless pedals.
        Since you're building your own, you could always replace the silicon diodes with tube diodes - maybe a 6AL5, or even a 12AX7 wired for diode operation.
        -tb

        "If you're the only person I irritate with my choice of words today I'll be surprised" Chuck H.

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        • #5
          Color me intrigued.

          Can you elaborate, tboy? Where would I get a lesson (schematic?) on how exactly to do that? Got any links? I'm afraid I am, and will - despite the contradiction - always be, a newbie.

          It's been my experience that without diodes there is no compression and/or sustain. Would these act the same as the silicon in that regard?

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          • #6
            Howdy, boy?
            (sorry, I couldn't resist)
            I believe you if you say so.
            I fact, I *always* believe what musicians say about any given sound, although not always agree on what they *think* the reason is.
            Anyway, I guess here the tube preamp response is not flat, at all, and pre-distortion EQ is important.
            Don't know if the second triode clips . Even if it clips a little, it will add something useful.
            I fear (may be mistaken) that increasing pre-distortion bass will add little body and much mush/mud, but test it anyway.
            As usual: post your results, good or bad, we always learn from each other's experiences.
            Good luck.
            EDIT: forgot about the trafos: try all the usual suspects, it's an unusual combination, but somebody *might* have something similar. HV winding is not *that* critical, you can use a lowr voltage one, you can use a 100V one and a doubler.
            Last edited by J M Fahey; 03-15-2010, 09:15 PM. Reason: dead memory cells
            Juan Manuel Fahey

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            • #7
              Fuzz box builders are always trying different diode types (germanium, silicon, LED), and combinations of types (like one silicon and one germanium), to get different "flavors" of distortion; no reason to leave tubes out of the mix. You could even put in a switch (or two) to select various types and combinations, including tube.

              You can use the two triodes in a 12AX7 as diodes by connecting the grids to the plates (connect pin 1 to pin 2, and pin 6 to pin 7). Power the filaments as you normally would from the 6.3v supply. Connect your two tube diodes back-to-back (pin 3 to pin 6, and pin 8 to pin 1) just as the silicon diodes are in the W20 schematic, and away you go.
              -tb

              "If you're the only person I irritate with my choice of words today I'll be surprised" Chuck H.

              Comment


              • #8
                mouser, digikey, mcm, newark,... good luck!

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                • #9
                  Sounds easy enough. I think I'll give it a shot. Thanks, tboy.

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                  • #10
                    Best not believe me too much, JMF, I change my mind like my underwear (what, monthly?).

                    This TD-1 has a sibling called the TO-2 which is very similar but with tone controls and less gain. I've done some experimentation with the TO-2 and the second stage (with diodes removed) distorts only slightly, but that distinctive tone that I referred to is there with or without the diodes. Sort of a glassy squeak.

                    I changed the second stage coupling cap on the TO-2 to a .01 which may be a bit too big, but I can dial it back since it has a bass control. I think a .005 would be about right. I think I'll go to a .002 on stage one. If too big it'll be simple enough to change out.


                    The only change I've made to the TD-1 is to remove that 470p cap before the second stage grid. I hated the blunting effect it had on the treble ... made it muddy, then crunched it back up in the second stage. Ugly.

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                    • #11
                      Well the transformer is proving to be a PITA. Having trouble finding one that'll work.

                      I looked at the Matchless Hotbox - they used a hammond 269ex. Some diyers have used 369ex and 369gx. But these range in price from $48-74 and are awfully big for a pedal. Edcor said I might be able to use their xpwr082 EDCOR - XPWR082. What do ya'll think? Can I use that? It's priced right.

                      A couple more questions:

                      Can I just use a wall wart? I hate 'em but that may turn out to be my best option.

                      Do you guys know of any good surplus outlets where I might find something suitable?

                      What about a DIY tranny? Can I just make my own? Doesn't look like there's all that much to it.
                      Last edited by Boy Howdy; 04-06-2010, 05:30 PM.

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                      • #12
                        You can use the "Mac Tube" trick, using a small/cheap/available reverse connected 220(or 240)VAC<->12V AC transformer inside the pedal, to get b+ and an *external* 12VAC wall wart which powers filaments *and* the internal inverted transformer.
                        Juan Manuel Fahey

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                        • #13
                          I've used a 240v-to-12v toroidal tx for a valve OD pedal and it works great. You use a 12vac wall wart into the 240v/12v tx with the 12v serving as the primary - you get approx 240vac out the other end.

                          With a bridge rectifier to get your DC voltage, you get around 290vdc once you account for losses - perfect for a valve OD pedal.

                          The toroidal tx's I've used also had 115v taps on the 240v winding, so I get a low voltage option too which gives approx 145v and makes for a softer sounding OD.

                          I got mine from Rapid in the UK, but I looked last week and they're not stocking them any more
                          HTH - Heavier Than Hell

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                          • #14
                            Interesting ideas, guys. Thanks! But can someone confirm the Edcor? EDCOR - XPWR082
                            It looks like it would work fine. I just want to make sure, since I'm a babe in the woods about some of this stuff.

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                            • #15
                              It looks VERY good, it's the real deal.
                              Perfect for a preamp with 1 (one) 12A_7 and as many Op Amps as you like.
                              A real find !!
                              If it had a higher 6.3V rating (600mA) it would be even better.
                              Juan Manuel Fahey

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