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Thread: Got a Couple Mission Amps

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    Senior Member TD_Madden's Avatar
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    Got a Couple Mission Amps

    Two Tweedy Deluxes, one Super

    First tweedy built has the Paul C Mod, uses a Celestion Blue. Using a 5V4.

    Other tweedy has the "super" OT, a Reverend speaker, Paul C Mod, and the Bruce's Volume/Tone Mod. Using TAD 6L6C;s two 12AX7s and a GZ34 CopperCap.

    Super is stock, but I've cycled thru a number of speakers, finally settling on a combination of an Eminence CopperHead and a Weber 10F150T.

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    Last edited by Bruce / Mission Amps; 05-31-2006 at 04:18 PM.

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    Member Emeritus Forever Steve A.'s Avatar
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    Quote Originally Posted by TD_Madden
    Two Tweedy Deluxes, one Super

    First tweedy built has the Paul C Mod, uses a Celestion Blue. Using a 5V4.
    So how do you like the Paul C Mod in a 5E3? I like it a lot in my Princeton Reverb but I'm not sure I like it in my tweed deluxe...

    --Thanks!

    Steve Ahola

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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Thumbs up

    It is a subtle mod but not a waste of time.
    I like the mod but find it more useful in amps with a fixed bias, where the drive signal can be allowed to swing a little further before hitting the end of the actual fixed bias voltage causing cutoff.
    The mod is not so obvious in cathode biased amps, like a 5E3, where the plate voltage of the PI is lower and the bias voltage is only about 20v to 24v anyhow.
    In the cathode biased appplication with lower plate voltages, the PI has very little trouble swingiing that far with little distortion but, most fixed bias 6V6s amps have bias voltages of about 8v to 15v deeper negative then cathode biased ones.
    The Paul C mod allows the PI to go a little further in peak levels with less distortion in an amp that can use the extra swing.
    ______________
    Which reminds me....
    Since most of the readers here have a strong interest or have built a 5E3, they should try a fixed bias version of the 5E3 sometime for a nice tonal change, a few more clean watts and more power tube headroom.
    A very simple adjustable bias supply can be made with two 1/2w resistors, a small 22k-25k trim pot, a 1N4007 diode, a 47uF-100uF 100v E-cap and a 12" piece of wire to hook it all up.
    All you do is then ground the cathode(s) wire of the two 6V6 tubes and lift the grounded ends of the two 220K resistors and insert the new bias voltage there.
    Adjust the bias voltage so the power tubes are running about 9-10 watts each.
    With a 1K screen node dropping resistor, the amp can usually hit about 14 watts fairly clean.
    With a 3Hy-5Hy choke replacing the 5K resistor, a SOVTEK 5Y3GT, GZ30 (not a GZ34) or a NOS 5V4GA... and the new bias voltage reset so the power tubes are idling at about 9-10 watts, it will get into the 18 watt range...
    the American 18 watter, a new 5E3 mod kit I am working on producing.
    My newest 5E3 chassis even has the PEM nuts installed in it for mounting this choke and a larger output tranny to allow 6L6 operation if desired.

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    Last edited by Bruce / Mission Amps; 05-31-2006 at 04:23 PM.
    Bruce

    Mission Amps
    Denver, CO. 80022
    www.missionamps.com
    303-955-2412

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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Oh and to add to this...
    I forgot to mention... we now have available our own octal socket to 9pin adapters for running EL84s in your tweed Deluxe.
    My new MA20-18 power tranny also has a pair of high voltage taps that are 265vac for EL84s if you so desire.

    Bruce

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    Bruce

    Mission Amps
    Denver, CO. 80022
    www.missionamps.com
    303-955-2412

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    Member riscado's Avatar
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    bruce I'm going to add the fixed bias mod to my tweed deluxe, pretty soon, I'll probably post some samples when I have the time...

    by the way, why not use the weber fixed bias 5e3 circuit: https://weberspeakerscom.secure.poww.../5e3_schem.jpg

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    Last edited by tboy; 06-23-2006 at 08:35 PM.

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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    That schem is for a cathode biased amp.
    An easy bias supply to build is from a brownface era Deluxe.

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    Bruce

    Mission Amps
    Denver, CO. 80022
    www.missionamps.com
    303-955-2412

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    Member riscado's Avatar
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    but check at the bottom of the weber scheme, there is an alternate bias scheme for fixed biasing, wouldn't that work? (this is their version of the 5e3)

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    Junior Member Joe6v6's Avatar
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    Looks very similar to the fixed bias circuit bruce described to me. I may give it a try one day. I want to make it switchiable between cathode & fixed, I just read a post about a kendrick amp that has switchiable bias.

    JOE

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    Resistors not Transistors !

  9. #9
    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Quote Originally Posted by riscado
    but check at the bottom of the weber scheme, there is an alternate bias scheme for fixed biasing, wouldn't that work? (this is their version of the 5e3)
    Yes... that should work...
    I didn't see it.

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    Bruce

    Mission Amps
    Denver, CO. 80022
    www.missionamps.com
    303-955-2412

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    Lifetime Member Ray Ivers's Avatar
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    Bruce,

    Do your octal/9-pin adaptors have internal components, or are they direct pin-for-pin crossovers? I'm looking for the second kind, they seem kinda hard to find.

    Ray

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    About the Paul C mod ...

    Has anyone noticed a change in bass response using the Paul C mod? The mod will lower the input impedance of the PI, so if you use the same coupling cap before the PI, it ought to cut a little more bass compared to the stock circuit.

    Shea

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