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Thread: Traynor YBA-1 Odd Output

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    Member mhuss's Avatar
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    Traynor YBA-1 Odd Output

    I have a YBA-1 on the bench (a later '74-ish model), with a brand new Hammond OT (the one they make as a YBA-1 replacement). The amp has an oddly distorted output (see attached). The signal on both input grids looks clean, and I tried replacing the output tubes with no change. I carefully checked the socket solder joints, everything looks OK. Any suggestions?

    At low levels, it looks clipped on the positive side, at the signal gets hotter, the 'divot' in the top of the waveform gets deeper.

    The voltages on all pins look normal.
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    Last edited by mhuss; 02-25-2020 at 03:44 PM. Reason: more info

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    Supporting Member Jazz P Bass's Avatar
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    You may be seeing 'positive feedback'.

    Try lifting R33 in the feedback path.
    If the signal then is reduced at the output, reverse the OT primaries.

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    Member mhuss's Avatar
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    Thanks for the suggestion, I just tried that, no difference (ignoring the extra gain ). I would expect if the primary was reversed it'd be howling.

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    It doesn't have those funny brown sandbox 'protection' devices across the OT primaries does it?

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    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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    No, just power tube pin 3 connected directly to the primary (x2).

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    i would check the OT out of circuit for mismatched wiring

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    What are plate and screen voltages both measured directly at the sockets?

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    And check the grid and screen resistors, if you haven't.

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    Resistor problems will show from actual voltages.

    The observed signal asymmetry could be caused by:

    - a non-conducting power tube (including open connection to one side of the OT primary)
    - an open screen resistor.

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    Last edited by Helmholtz; 02-25-2020 at 05:21 PM.
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    OK, I have officially lost it. Alex and Helmholtz are both pointing in the right direction.

    The primary connections are blue, red, brown. With the primary disconnected:
    bu-bn = 54 ohms
    bn-rd = 54 ohms
    rd-bu = 780 ohms!!!
    How is this even possible? Has Ohm's law been repealed?
    I measured and remeasured several times, both polarities. Same result. What the heck is going on?

    EDIT: When all else fails, read the directions. On this particular transformer, red is the end and brown is center. So much for "following the original color code as much as possible."

    I connected it with brown to B+ and red to the tube and now it's working OK.

    I still don't get those resistance measurements, though...

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    Last edited by mhuss; 02-26-2020 at 01:43 AM.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by mhuss View Post
    EDIT: When all else fails, read the directions. On this particular transformer, red is the end and brown is center. So much for "following the original color code as much as possible."
    Why would they do that!?!

    Ok, but they put it in the literature. But why would they do that!?! What could possibly have been wrong with "red = B+"???

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

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    Eh, probably some junior engineer with no history/experience. They let go of the old guy because he was costing too much.

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    Supporting Member The Dude's Avatar
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    Agreed. Yes it's in the lit, but what about convention? I don't want them wiring my house........ special notes ("green is hot") in the breaker panel and all.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by The Dude View Post
    Agreed. Yes it's in the lit, but what about convention? I don't want them wiring my house........ special notes ("green is hot") in the breaker panel and all.
    ..."Except where we haven't rewired. We don't have complete notes on where that is"...

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    Last edited by Chuck H; 02-26-2020 at 10:39 PM.
    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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    For future reference, the Red and Brown are swapped and Blue stays where it is (for proper phase with the NFB) on a Hammond 1750G. Other variants (like the 1750RA) have the colors correct.

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    The primary connections are blue, red, brown. With the primary disconnected:
    bu-bn = 54 ohms
    bn-rd = 54 ohms
    rd-bu = 780 ohms!!!
    How is this even possible? Has Ohm's law been repealed?
    I measured and remeasured several times, both polarities. Same result. What the heck is going on?
    Many DMMs have problems to correctly measure DCR if it hides behind a large inductor like an unloaded transformer.
    Short the secondary while measuring primary DCR for a reliable reading.

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    Ah - interesting and good to know. Thanks!

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    Yeah, mine the auto ranging can't figure out what range to use.

    If I manually select the 2k ohm range it reads the trans resistance.

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    Quote Originally Posted by drewl View Post
    Yeah, mine the auto ranging can't figure out what range to use.

    If I manually select the 2k ohm range it reads the trans resistance.
    Inductors don't like switching/pulsing signals, so they react with counter-EMF, thwarting the measuring current. This in turn may drive the meter crazy.
    Shorting the coupled secondary essentially shorts the inductive part of the primary impedance.

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    Last edited by Helmholtz; 02-27-2020 at 01:00 PM.
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    My electric fence energisers show a pulse on my DMM when measuring DCR of larger inductors.

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    Don't forget the joker g1's Avatar
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    Quote Originally Posted by Chuck H View Post
    Why would they do that!?!

    Ok, but they put it in the literature. But why would they do that!?! What could possibly have been wrong with "red = B+"???
    I've run into this with other Hammonds as well. Also the secondary side colours. And other manufacturers. Bottom line is verify before trusting 'conventional' wiring colour schemes. Doesn't help that much when someone gets their own scheme wrong though (commonly seen in single ended OT primary side colours).

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by g1 View Post
    I've run into this with other Hammonds as well. Also the secondary side colours. And other manufacturers. Bottom line is verify before trusting 'conventional' wiring colour schemes. Doesn't help that much when someone gets their own scheme wrong though (commonly seen in single ended OT primary side colours).
    Ok, yeah. Completely agree. So... Hammond now manufactures clones for guitar amps from all major brands. Surely they know the old Fender standard of red (ct) brown and blue (either end) for the OT primary winding. It seems really dumb to use the same colors for another OT primary they manufacture, but allocate the colors differently.

    Like a deli that makes peanut butter/jelly sandwiches, but also egg salad/tuna salad sandwiches suddenly deciding to make peanut butter/tuna salad sandwiches and egg salad/jelly sandwiches. One shouldn't mix the ingredients together in dangerous ways.

    I said "it seems really dumb" earlier because I don't even know if Traynor ever used the red, blue, brown color scheme allocated as Hammond provided. If they ever did then I guess it's just an unfortunate misunderstanding.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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    Bent Member Chuck H's Avatar
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    Ok... I just went and looked at a bunch of YBA-1's and they all seem to use red as B+ for the the OT primary. And usually brown and some cool color (blue, aqua, green, etc.) for either end. It's hard to tell what the end colors actually are because of variable photo quality and lighting. My own Bassmaster is currently hard to get to at the bottom of a stack of back burner projects (no flames please, it's a later 2x2 input model ). I'm not sure that would be an accurate witness anyhow. But for the old YBA-1's, yeah, it's red (ct), brown and some cool color for either end. So... Not a smart move under any circumstances to make red one of the winding ends on that transformer. I can't think of a single good reason to do it, but I can think of a few very good reasons not to. Just my humble opinion.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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    Epilogue: I contacted Hammond, they said "you're correct, it's wrong, we'll make an engineering change and fix it in future batches." Also, they said they couldn't believe no one had said anything about it before, it's been that way for 15 years. lol.

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    Supporting Member The Dude's Avatar
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    It makes you wonder how many are out there installed incorrectly or if anyone just gave up on an amp because they couldn't get it to work with OT wires as they thought they should be.

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    Right?

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