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Thread: Gotta a power transformer, can't seem to decided what to do with it - any thoughts ???

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    Member kevtronic's Avatar
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    Gotta a power transformer, can't seem to decided what to do with it - any thoughts ???

    So, I've got a power transformer I picked up a while ago that has been sitting and collecting dust. Figured I'd build something around it, but I can't really seem to decide just what I want to to build around it. So, I figured for the hey/fun of it I'd post the specs here and see if someone may have some idea's or suggestions.

    About the only thing I know for sure is I want reverb and tremolo. The reverb will most likely be tube driven (not tranny driven) and the tremolo will most likely be one half a dual triode tube. So, essentially a 12ax7 and a 12au7 for those. With this tranny it's almost certain to be push/pull and I was thinking of using the long tail phase inverter. So, three dual triode preamp tubes at this point.

    I've got 5y3, 5U4GB, and GZ34 tubes on hand and plenty of diodes for rectification.

    I've got plenty of el84 tubes and a couple 6l6wxt output tubes on hand, but I can buy power tubes If need be - don't necessarily have to use what I have on hand.

    I've also got a fair selection of dual triode preamp type tubes on hand.
    I actually got some 7-pin power tubes and preamp tubes, but not thinking the power tubes will come in play with this tranny.

    This is just all for fun, and low key, to build an amp for the hey of it, to use up a nice power transformer that needs a tube amp to call home.
    Generally I just decide what I'm building and do it, but I'm curious what someone else might do with this tranny if they had it.

    Here are the specs for the power transformer:
    550 VCT @ 173 mA: 275-0-275 , 173mA , 5v @ 3A , 6.3v @ 5A
    The 6.3v is center tapped.
    It's a newer production tranny design for USA mains, so specs should be real close (it's a hammond tranny).

    Thanks either way ahead of time...

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by kevtronic View Post
    So, I've got a power transformer I picked up a while ago that has been sitting and collecting dust. Figured I'd build something around it, but I can't really seem to decide just what I want to to build around it. So, I figured for the hey/fun of it I'd post the specs here and see if someone may have some idea's or suggestions.

    About the only thing I know for sure is I want reverb and tremolo. The reverb will most likely be tube driven (not tranny driven) and the tremolo will most likely be one half a dual triode tube. So, essentially a 12ax7 and a 12au7 for those. With this tranny it's almost certain to be push/pull and I was thinking of using the long tail phase inverter. So, three dual triode preamp tubes at this point.

    I've got 5y3, 5U4GB, and GZ34 tubes on hand and plenty of diodes for rectification.

    I've got plenty of el84 tubes and a couple 6l6wxt output tubes on hand, but I can buy power tubes If need be - don't necessarily have to use what I have on hand.

    I've also got a fair selection of dual triode preamp type tubes on hand.
    I actually got some 7-pin power tubes and preamp tubes, but not thinking the power tubes will come in play with this tranny.

    This is just all for fun, and low key, to build an amp for the hey of it, to use up a nice power transformer that needs a tube amp to call home.
    Generally I just decide what I'm building and do it, but I'm curious what someone else might do with this tranny if they had it.

    Here are the specs for the power transformer:
    550 VCT @ 173 mA: 275-0-275 , 173mA , 5v @ 3A , 6.3v @ 5A
    The 6.3v is center tapped.
    It's a newer production tranny design for USA mains, so specs should be real close (it's a hammond tranny).

    Thanks either way ahead of time...
    So what your asking for is a deluxe reverb is what comes to my mind. I'd want to build a 6g6 and add the trem and reverb.

    nosaj

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    Bent Member Chuck H's Avatar
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    I might use it for those 6l6's with a hot bias and and a bias wiggle trem (and I'd dedicate two triodes for that). Use the GZ34 and probably get a B+ around 350V and 30W clean. Magic trem and just about the perfect wattage for gigs.

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    Don't forget the joker g1's Avatar
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    The spec's look like Hammond 270FX. Some of the amps that come up for that are 4 x 6BQ5.

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    Member kevtronic's Avatar
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    Quote Originally Posted by g1 View Post
    The spec's look like Hammond 270FX. Some of the amps that come up for that are 4 x 6BQ5.
    Actually that is what the tranny is and I was actually thinking about going with 4 el84's to eat up some of the filament current available.

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    Quote Originally Posted by Chuck H View Post
    I might use it for those 6l6's with a hot bias and and a bias wiggle trem (and I'd dedicate two triodes for that). Use the GZ34 and probably get a B+ around 350V and 30W clean. Magic trem and just about the perfect wattage for gigs.
    I was wanting to use up the 6L6's. I'll have to check into again. I could always tweak the filament voltage down some if it was a bit high when all was said and done.

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    Quote Originally Posted by nosaj View Post
    So what your asking for is a deluxe reverb is what comes to my mind. I'd want to build a 6g6 and add the trem and reverb.

    nosaj
    A Fender Bassmen with tremolo and reverb - I would like to use up my 6L6wxt+ tubes - sounds like cool project - The Bass-O-Trem-O-Verb

    So, everyone is pretty much on the same pages I am on.
    So, probably best match - 4 el84's, with most interesting 6L6 tweaky bend and twist project based on the two 6L6 amp suggestions.
    Thanks for all the input guys - appreciate it.
    I think I'll call it one or the other - it's now narrowed down to two
    Thanks again.

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by kevtronic View Post
    A Fender Bassmen with tremolo and reverb - I would like to use up my 6L6wxt+ tubes - sounds like cool project - The Bass-O-Trem-O-Verb
    NOW you're talkin'! Can't say I've ever seen such a thing, but that sounds like a sweet combination.

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    HV current is a bit light on for 4 x EL84/6BQ5, also light on for 2 x EL34
    The 2 x 6L6WXT seems a better fit
    OR
    4 x 6V6GT into a 4K3 to 5K Raa output Tranny would also work.

    Weirder:
    2 x KT66 into about 5K Raa
    2 x KT88 in Ultralinear about 5K Raa


    Cheers,
    Ian

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    Well, every one who has posted is pretty much on the same page I am. Great input and appreciated. However, I still can't get myself to sacrifice a chassis for this transformer. With that I like to say thanks for the input, but I guess for now I am going to put it back on the shelf to collect dust for a while. Bass-o-trem-verb, gotta love it. If nothing else I think this short thread produced a cool name and idea

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    Valvulados.com jmaf's Avatar
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    Quote Originally Posted by kevtronic View Post
    Well, every one who has posted is pretty much on the same page I am. Great input and appreciated. However, I still can't get myself to sacrifice a chassis for this transformer. With that I like to say thanks for the input, but I guess for now I am going to put it back on the shelf to collect dust for a while. Bass-o-trem-verb, gotta love it. If nothing else I think this short thread produced a cool name and idea
    Gotta be an amp?

    Perhaps try a different kind of project like a tube tester or a tube matcher?

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    Gotta say those are two things I didn't think of. Got a tube test. Don't have a dedicated tube matcher, however I'm clueless on how one would make a diy tube matcher.

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    Valvulados.com jmaf's Avatar
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    Quote Originally Posted by kevtronic View Post
    Gotta say those are two things I didn't think of. Got a tube test. Don't have a dedicated tube matcher, however I'm clueless on how one would make a diy tube matcher.
    I'm planning on starting a open-source tube matcher project which I'd share here, but I don't have the time right now. I do have it on my to-do list though.

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    Well, like I said, I have no clue on what it'd take, as I've never thought about it, and I'm not sure how much I could contribute to such a project/thread, but it sure seems like a great idea for a project/thread. Tube test wise I just use an old tester I purchased that was had already been gone thru and calibrated - it actually works quit well and it's like in a military grade metal case. So, sounds like a cool thread. If you start it and can remember message/email me about it - I'd like to tag along with it if nothing.

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    Supporting Member eschertron's Avatar
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    Quote Originally Posted by jmaf View Post
    Perhaps try a tube matcher?
    You mentioned that, and now I can't put the idea out of my head, so...


    HV for B+, probably doesn't need too much filtering?
    bias supply, variable over a wide range?
    I have a couple 0..100mA meters for real-time comparison testing of plate or cathode current. Or maybe both plate and cathode, and have a single socket.
    I'm still trying to imagine a jig to compare the current differential between two tubes. Two 1R resistors on the cathodes and measure mV difference at the cathode pins? I guess that could be done on any amp with bias test points.

    Who's done this before?

    edit: of course I should be looking at bias current too, but my assumption is that plate dissipation is what tells how closely the tubes match at any given bias voltage.

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    Last edited by eschertron; Yesterday at 09:21 PM.
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    Valvulados.com jmaf's Avatar
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    Quote Originally Posted by eschertron View Post
    You mentioned that, and now I can't put the idea out of my head, so...


    HV for B+, probably doesn't need too much filtering?
    bias supply, variable over a wide range?
    I have a couple 0..100mA meters for real-time comparison testing of plate or cathode current. Or maybe both plate and cathode, and have a single socket.
    I'm still trying to imagine a jig to compare the current differential between two tubes. Two 1R resistors on the cathodes and measure mV difference at the cathode pins? I guess that could be done on any amp with bias test points.

    Who's done this before?

    edit: of course I should be looking at bias current too, but my assumption is that plate dissipation is what tells how closely the tubes match at any given bias voltage.
    Filtering: it depends on what you want to spend on the project. If you've got the components and $ then there's no reason not to build a hard PS. Remember : testing with class A bias will set the tube to 100% power consumption, so you'll get ripple unless it's hard PS. Sag isn't important, ripple probably is depending on how you plan on measuring currents.

    Bias: 0 to -50 maybe?

    Bias current? You plan on matching using AC signals? If matching in DC at a fixed point then you won't need to measure any bias current. Unless I understood what you meant incorrectly.

    Differential current: it'd be neat if you had an analog needle centered galvanometer and the needle moved to the side of the tube with more current. Matched tubes would show the needle exactly on center.

    If you build a regular output stage with 1R resistors on cathode, all you need really is a dual channel oscilloscope to match any pair of tubes. Just tap the reading off the cathodes and view the difference right on screen.

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    Supporting Member eschertron's Avatar
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    Quote Originally Posted by jmaf View Post
    Bias current? You plan on matching using AC signals? If matching in DC at a fixed point then you won't need to measure any bias current. Unless I understood what you meant incorrectly.
    I think I wrote what I meant incorrectly. Slow brainwave day on Monday. Upon reflection, I would expect exactly zero current through the control grid for any of this bias voltage only applied to grid testing.

    And yes, dual-channel scope on 1R sense resistors allows me to read individual and differential currents with a flick of a switch. I was simply (again, Monday) thinking of a more Golden-Age-Appropriate type of test rig. Kind of 50s sci-fi with gauges and dials.

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    Valvulados.com jmaf's Avatar
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    Quote Originally Posted by eschertron View Post
    I think I wrote what I meant incorrectly. Slow brainwave day on Monday. Upon reflection, I would expect exactly zero current through the control grid for any of this bias voltage only applied to grid testing.

    And yes, dual-channel scope on 1R sense resistors allows me to read individual and differential currents with a flick of a switch. I was simply (again, Monday) thinking of a more Golden-Age-Appropriate type of test rig. Kind of 50s sci-fi with gauges and dials.
    Since the last post I got my mind set on one of these:

    Click image for larger version. 

Name:	galvanometer.jpg 
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    I'd drill the test tube sockets holes to each side of it on the chassis. The needle would point to the hotter tube. A perfectly centered needle means matched tubes.

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    Quote Originally Posted by eschertron View Post
    ...dual-channel scope on 1R sense resistors allows me to read individual and differential currents with a flick of a switch. I was simply (again, Monday) thinking of a more Golden-Age-Appropriate type of test rig. Kind of 50s sci-fi with gauges and dials.
    Yes, monitoring the signal at cathode current sensing resistors is invaluable for assessing weaker tubes in a p-p set; for a 4 power tube amp, it massively simplifies the task.

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    Supporting Member eschertron's Avatar
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    Quote Originally Posted by pdf64 View Post
    Yes, monitoring the signal at cathode current sensing resistors is invaluable for assessing weaker tubes in a p-p set; for a 4 power tube amp, it massively simplifies the task.
    If building a dedicated test jig, is there an advantage to sensing current at the anode versus at the cathode? Short of 'proving out' how much current flows at anode and screen, would it be desirable (or even possible) for a tech to identify tubes with wonky/damaged screens by the ratio of anode/screen current that might not be detected by simply looking at the current sum at the cathode?

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    I suspect that bad screens generally identify themselves pretty well with fault current, arcs etc. Trying to assess screen to plate current ratio and quantify a 'go/no go' point is probably taking things further than manufacturer's / vendors QA bother with.

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