Incoming new 6L6 build, need advice on voltage

Discussion in 'Shock Brother's DIY Amps' started by allesz, Jan 10, 2020.

  1. allesz

    allesz Tele-Meister

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    Hallo, I am in the process of start building an amp, parts are on their way.

    It will be a cathode biased push pull of two 6L6; I would like to use EL34 actually, but it happens that I have some 6L6 in the hose, the output transformer has a 6600 Ohm input impedance (with 4, 8 and 16 outs), so I think I will stick with what I have.

    Only problem is that the PT will put out only about 380 DC volts when rectified (solid state recto btw).

    Is it too low for 6L6? I could go to 6v6, the OT should be good, provided I use the 16 ohm out for a 8 ohm cab.

    What would you do?
     
  2. Dacious

    Dacious Poster Extraordinaire

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    No should work fine. 6600 primary is probably better suited to 6V6.
     
  3. allesz

    allesz Tele-Meister

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    Thank you.

    I always see voltages around 400 V or more for 6L6 so I'm a little worried.

    For 6V6 I woulg go higher than 6600 Ohms primary impedance, maybe 9000? Anyway I actually plan to switch between 6L6 and 6V6... only I have 6L6 around right now.
     
  4. FenderLover

    FenderLover Poster Extraordinaire

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    These numbers tend to be used interchangeably in many applications because larger, more powerful, amps using 6L6 have more current to support their power. More power for a given voltage requires more current and less resistance (the reflected load). The mistake people make is automatically dropping down the output tap when switching from 6V6 to 6L6 in an amp where the output power is about the same with either. It's not a requirement, it's a subjective recommendation.

    Bottom line is you didn't say anything about the current capacity of your PT. Power is a function of voltage and current. If it's an amp where the output power is limited by the PT current and 6L6 isn't really any more powerful than with 6V6, there's no reason to change the OT load - unless you want to experiment. If the PT can truly support 6L6 to higher power capacity, a lower reflected primary load would be a better electrical match.

    Sometimes these things can be confusing, but think about what amplifier your amp might be similar to and look up specs for the transformers used. It's a good sanity check and may provide a starting baseline for you.
     
  5. tubelectron

    tubelectron Tele-Holic

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    It's fine, no issue... ;)

    You can expect a 20 to 25W RMS clean tone power output with that 6L6 setup.

    On the Black and White amp below (12") :

    I have 22W RMS clean tone output power (onset of clipping, diodes mode) with 2x6L6GAY in cathode bias 235R (2x 470R //).

    Cathode voltage = 24.3VDC
    Plate voltage = 348VDC
    Screen voltage = 347VDC
    Load = 5000R plate to plate / 8R

    On the Green amp below (10") :

    I have 24W RMS clean tone output power (onset of clipping) with 2x5881 in fixed bias.

    Grid (bias) voltage = -30VDC
    Plate voltage = 380VDC
    Screen voltage = 350VDC
    Load = 6200R plate to plate / 8R

    [​IMG]

    [​IMG]

    -tbln
     
  6. allesz

    allesz Tele-Meister

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    Thanks.
    The PT puts out 3A on the filament supply and 150mA on the high voltage tap.

    I will start building, and keep you updated.

    Btw, I bet It won't be nice as tubelectron's ones... :-0
     
  7. Jon Snell

    Jon Snell TDPRI Member

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    Stick with 6L6 as the filament tapping won't support EL34s. ECC83/12AX7s as pre-amp/phase convertor? Would be a good choice or old school 6SL7.
     
  8. FenderLover

    FenderLover Poster Extraordinaire

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    That'll work perfect with 6.6K OT and 380V B+. Looking forward to your build.
     
  9. allesz

    allesz Tele-Meister

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    After dinner I drilled the holes in the chassis, a recycled peavey dead combo. It was made of iron... My sissy harms are tired now.

    The big holes for the octal tubes were quite a pain; and of course my tools are not the best for the task.

    In the next days I'll start mounting the hardware, and maybe post some pics (in a new thread?).

    An hot shower and bed we go.
     
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