Switching a Traynor YBA-2a back to 12AX7 from EF86 in V1

Discussion in 'Amp Tech Center' started by NBS2005, May 29, 2020.

  1. NBS2005

    NBS2005 TDPRI Member

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    Hi all,

    The '67 YBA-2a I have is modded and running an EF86 tube in V1. I bought this thing to mod and learn a little bit so I wanted to talk about how I would return this to running a 12AX7 in V1. I'm at the very beginning of this journey in learning how to do this.

    First off, I need to get a hold of the schematic for the stock amp. I'm pretty sure I can dig that up. Next, I'd need to figure out what was done. I'll open it up and post some pics. This is from the previous owner when I bought it:

    It’s quite different from stock now. It has the first 12AX7 replaced by an EF86 and I changed the phase inverter from the original cathodyne style to a long tail pair.

    Rummaging around on the web I found this; don't know if it's valuable info or not.

    The simplest way would be to simply rewire the socket for parallel 12AX7:

    -- Completely remove the 1M resistor and 0.1uF capacitor (and wire if present) connected to pin 1

    -- Detach the heater wire connected to pin 5

    -- Detach the grid wire connected to pin 9

    -- Connect a jumper between pins 4 and 5, leaving the heater wire on pin 4

    -- Connect a jumper between pins 1 and 6, leaving the plate wire/resistor on pin 6

    -- Connect a jumper between pins 2 and 7

    -- Make sure there is a jumper between pins 3 and 8, and connect one if not present, leaving the cathode wire/resistor on pin 3

    -- Connect the (detached) grid wire to pin 2

    -- Connect the (detached) heater wire to pin 9


    That should get you started. It may seem a bit intimidating, but it's not really that hard. The plate and cathode resistor values may need to be adjusted to get the best sound. You could go as low as 47k on the plate and 470 on the cathode. I'd see if just converting the socket gives you what you want before experimenting with resistor values, though.



    Thanks for the help.

    Jeff
     
  2. Wally

    Wally Telefied Ad Free Member

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    https://el34world.com/charts/Schematics/files/Traynor/Traynor_bassmate_yba2.pdf

    There is the schematic.fwiw, beware of what you have there. That original circuit does not have a cathodyne PI but rather has a type of paraphrase inverter. One might be at least a tiny bit wary of any changes in any amp.....be curious about the actual results of someone’s modification.
    If I understand your experience properly, I would suggest studying tube elements and functions thereof. if you can read a schematic, then you may be farther along than that and could skip the tube element study. imho, it would be a good thing to study exactly what is there.....if you can read a schematic to s9me degree you can draw the circuit in front of you out 8n a schematic form. That is a good approach as a basis for modifying the amp or taking it back to stock format. I would suggest going back to stock first. Then, if you want to go with paralleled triode in V1 or to use that unused triode for a second gain stage. Either one of those things is not a beginner project...imho.
    or....if one really likes how the amp works now, one might study it hard and long before changing it. I have come to like pentode preamps with simple tone stacks and cathode outputs.
    Good luck with it.
     
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  3. NBS2005

    NBS2005 TDPRI Member

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    Thanks Wally. As I dig into this I'm starting to agree this may be more than I can chew. I might chat with my local tech and get his thoughts.

    In an interesting note I swapped the Phillips and Sylvania 6v6 in this with the ELectro Harmonix 6v6Gt matched pair that was in my Harmony 305. Both amps sound better. Go figure.
     
  4. Wally

    Wally Telefied Ad Free Member

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    Whenever you replace the power tubes, the bias is changed. Sometimes that is the reason for the difference in sound. Until one takes measurements before and after changing the tube/s one never knows exactly why the Sonics change. That is why I don’t put much stock into claims of such and such tube making a big change in an amp unless there are comparative bias numbers taken and shared.
    I don’t discount the change. I simply ap cannot assume exactly why the change took place. If you had some identical EH 6V6s with different operational specs, those would change the sound again, ime.

    The internet is ful”mod information for free these days. It was necessary to buy books back before the ‘net came along if one wanted to study tubes, schematics, amps. Now all one has to do is do s9me search. The Wikipedia page on Vacuum Tube History is a good basic introduction, imho. The Tube Data Sheet Locator Page is a great place to get info on almost any tube. Schematics can be found at Schematic Heaven, El 34 World schematics, amp repair parts schematics. I spent a small fortune on books to get some of that information.
    I advise reading the Tech Pages at Aiken Amps. If one wants to buy books, that is still a good avenue, imho.
     
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  5. Wally

    Wally Telefied Ad Free Member

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    Rob Robinette...robrob on this forum....has a site full of good info. That Traynor would be a good circuit to learn on, I would imagine.
    One could build a Fender 5D3 Deluxe there quite simply....or a 5F10 Harvard.....lots of options. But....if it was well done, the mods that you have there right now described would yield a hotter amp, ime, than the stock circuit.
     
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  6. KeepItSimpleTele

    KeepItSimpleTele TDPRI Member

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    Return it to stock! :) These things rocked just as they came from the factory on 6v6 tubes. I have two of the heads and love em :)
     
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