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New Amp Build: BYOC Brit 45 with JTM50 modification
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Thread: New Amp Build: BYOC Brit 45 with JTM50 modification

  1. #1
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    Default New Amp Build: BYOC Brit 45 with JTM50 modification

    Just finished this new amp build last week. I started with the BYOC "Brit 45" kit (Marshall JTM45 clone), but modified it to a JTM50, albeit one with a tube rectifier and a variable voltage regulator (VVR) on the power supply circuitry. You can see the VVR module mounted to the back of the chassis between the AC socket and the output impedance rotary switch; the dual-gang pot that controls the voltage levels is next to the black output jack. The VVR enables this non-MV amp to achieve tube overdrive at much more reasonable volume levels, thereby preserving my hearing and my marriage. It runs a pair of EL34 output tubes, rather than the KT66's classically used in the JTM45. At the bottom of the photos, I've posted a marked up Brit 45 schematic that shows all the modifications that were made in red.

    It sounds, well, just like you'd expect a 50W Marshall to sound. I jumper the Normal and High Treble channels together and blend in the amount of treble I want with the two volume controls. It takes pedals extremely well, though you obviously have to keep the overall gain reigned in a bit when using time-shift effects (chorus, delay, reverb, etc.). The crunch tone with a Tube Screamer type overdrive is to die for.

    And it's PURPLE, my favorite color!









    DVM's Ever-Expanding Gear List:

    Guitars - '05 Gibson Historic '59 RI (R9); '11 PRS Studio; '08 Heritage H-555; '12 Fender Am. Std. Strat; '89 Fender Strat Plus; '02 Fender Telecaster '72 Thinline RI; '15 Gretsch G5420T Electromatic; '97 Godin LGX; '12 G&L Tribute ASAT Classic Bluesboy SH; " Kwik-Keef Konvertible" '09 Squier CV '50s Tele; '10 Squier CV Tele Custom; '13 Cabronita Thinline Tele; '14 Squier CV Strat HSS; '15 Squier CV "Humcaster" homemade Strat; '15 Squier CV "Lipstick Fiesta" homemade Strat; '10 Agile AL-3000; '12 Xaviere XV-890HSS; '09 Hagstrom Ultra Swede; '15 Slick SL60; '16 Slick SL-57; '16 SX Ursa2 MN5 Bass; '05 Martin HD-28; '12 Epiphone Masterbilt DR-500MCE; '71 Yamaha FG-300

    Amps & Cabs - Mesa Boogie Mark Five:25 head; Mojave Coyote head; Fender Hot Rod Deluxe Lacquered Tweed Ltd. Ed.; Allen Sweet Spot kit amp; BYOC Tweed Royal kit amp; Homebuilt 1.5W Firefly Head; Epiphone Valve Jr. combo + mods; Drive 2x12 cab / Celestion G12M Greenback + G12H30; AB Custom Audio 1x12 cab / Celestion Alnico Blue

    Pedals/Effects - ZILLIONS, including DVM's Home-built Pedals - See some HERE and HERE, TOO!

    DVM's Gear Photos
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  2. Likes sunvalleylaw liked this post
  3. #2
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    WOW......nice work. Should really sing. Congrats!

  4. #3
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    You know what would go perfectly with that amph?

    Axen: Jackson DK2M, Fender Deluxe Nashville Telecaster, ESP LTD Surveyor-414
    Amphen: Jet City JCA22H and JCA12S cab, Carvin X-60 combo, Acoustic B20
    Effecten: "Thesis 96" Overdrive/Boost (aka DVM OD2), Hardwire DL-8 Digital Delay/Looper, DigiTech Polara Reverb, DigiTech EX-7 Expression Factory and CF-7 Chorus Factory, Danelectro CF-1 Cool Cat Fuzz
    "I don't need no instructions to know how to rock!"--Carl Brutananadilewski

  5. #4
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    Nah, I could hurt myself (or others) with that thing. I'll go with one of these:

    DVM's Ever-Expanding Gear List:

    Guitars - '05 Gibson Historic '59 RI (R9); '11 PRS Studio; '08 Heritage H-555; '12 Fender Am. Std. Strat; '89 Fender Strat Plus; '02 Fender Telecaster '72 Thinline RI; '15 Gretsch G5420T Electromatic; '97 Godin LGX; '12 G&L Tribute ASAT Classic Bluesboy SH; " Kwik-Keef Konvertible" '09 Squier CV '50s Tele; '10 Squier CV Tele Custom; '13 Cabronita Thinline Tele; '14 Squier CV Strat HSS; '15 Squier CV "Humcaster" homemade Strat; '15 Squier CV "Lipstick Fiesta" homemade Strat; '10 Agile AL-3000; '12 Xaviere XV-890HSS; '09 Hagstrom Ultra Swede; '15 Slick SL60; '16 Slick SL-57; '16 SX Ursa2 MN5 Bass; '05 Martin HD-28; '12 Epiphone Masterbilt DR-500MCE; '71 Yamaha FG-300

    Amps & Cabs - Mesa Boogie Mark Five:25 head; Mojave Coyote head; Fender Hot Rod Deluxe Lacquered Tweed Ltd. Ed.; Allen Sweet Spot kit amp; BYOC Tweed Royal kit amp; Homebuilt 1.5W Firefly Head; Epiphone Valve Jr. combo + mods; Drive 2x12 cab / Celestion G12M Greenback + G12H30; AB Custom Audio 1x12 cab / Celestion Alnico Blue

    Pedals/Effects - ZILLIONS, including DVM's Home-built Pedals - See some HERE and HERE, TOO!

    DVM's Gear Photos
    Visit MY WEBSITE!



  6. #5
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    Looks great! I bet it sounds great too!
    Steve Thompson
    Sun Valley, Idaho


    Guitars: Fender 60th Anniversary Std. Strat, Squier CVC Tele Hagstrom Viking Semi-hollow, Joshua beach guitar, Martin SPD-16TR Dreadnought
    Amphs: Peavey Classic 30, '61 Fender Concert
    Effects and such: Boss: DS-1, CE-5, NS-2 and RC20XL looper, Digitech Bad Monkey, Korg AX1G Multi-effects, Berhinger: TU100 tuner, PB100 Clean Boost, Line 6 Toneport UX2, Electro Harmonix Little Big Muff Pi, DuhVoodooMan's Rabid Rodent Rat Clone, Zonkin Yellow Screamer Mk. II, MXR Carbon Copy Delay


    love is the answer, at least for most of the questions in my heart. . .
    - j. johnson

  7. #6
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    I want that amph!
    The Law of Gravity is nonsense. No such law exists. If I think I float, and you think I float, then it happens.
    Master Guitar Academy - I also teach via SKYPE.

  8. #7
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    Hi duvoodooman,

    Where did you dig up the info concerning the differences between the JTM45 and the JTM50? I've build a JTM45 clone using the BYOC schematic which I like best compaired to the diagram which was accompanied with the kit. Concerning the JTM50 schematic it is very hard to find any info on the web. It also seems that there are many different versions made by Marshall at that time. I've been asked by the owner of the JTM45 clone to modify it to a JTM50 but like to go shure what is realy req'd. Why did you relocate the 2 1M resistors at the input circuit and why did you add the 100nF cap's?

  9. #8
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    DVM doesn't check in as much as he used to, but hopefully he'll see your post an give you an answer. Knowing him I'm sure there was a good reason for doing what he did!
    Ah, nothing relieves the discomfort of GAS pains like the sound of the UPS truck rumbling down your street. It's like the musician's Beano.

  10. #9
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    Bloozcat - just saw your signature line !
    "GAS never sleeps" - Gil Janus

    "Now you got to pay your dues. Get that axe and play the blues." - Spudman

    Gear: Epiphone Sheraton II, Epiphone Wildkat, Epiphone Emperor Joe Pass, Fender MIM Strat, Tacoma DR-14, Johnson JR-200 resonator; Fender Super Champ XD amp

  11. #10
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    Kentuckytukker and I exchanged PMs and some emails and I provided him with all the info I had on this modification. The short answer to his question is that the main changes are EL34 output tubes, a different OT to match up with them, some additional DC filtering, a different cathode resistor and bypass cap on the High Treble input triode, and some associated resistor value changes related to these mods. A bunch of the changes shown in red are associated with the addition of a variable voltage regulator, including the three 100 nf capacitor/1 Mohm resistor pairs and have nothing to do with the JTM50 conversion, per se. (As it turned out, the VVR was NOT a good addition to this amp; the one I used was a prototype I got from Keith at BYOC, and it turned out to lack enough heat dissipation to keep it from burning up after a fairly short amount of use, necessitating quite a bit of repair work.)

    I'm not sure exactly when Marshall switched from a tube rectifier to solid state rectification on the JTM amps, as I've seen JTM50 schematics both ways. By the time the 50W "Plexi" came out, they were all SS rectification.
    DVM's Ever-Expanding Gear List:

    Guitars - '05 Gibson Historic '59 RI (R9); '11 PRS Studio; '08 Heritage H-555; '12 Fender Am. Std. Strat; '89 Fender Strat Plus; '02 Fender Telecaster '72 Thinline RI; '15 Gretsch G5420T Electromatic; '97 Godin LGX; '12 G&L Tribute ASAT Classic Bluesboy SH; " Kwik-Keef Konvertible" '09 Squier CV '50s Tele; '10 Squier CV Tele Custom; '13 Cabronita Thinline Tele; '14 Squier CV Strat HSS; '15 Squier CV "Humcaster" homemade Strat; '15 Squier CV "Lipstick Fiesta" homemade Strat; '10 Agile AL-3000; '12 Xaviere XV-890HSS; '09 Hagstrom Ultra Swede; '15 Slick SL60; '16 Slick SL-57; '16 SX Ursa2 MN5 Bass; '05 Martin HD-28; '12 Epiphone Masterbilt DR-500MCE; '71 Yamaha FG-300

    Amps & Cabs - Mesa Boogie Mark Five:25 head; Mojave Coyote head; Fender Hot Rod Deluxe Lacquered Tweed Ltd. Ed.; Allen Sweet Spot kit amp; BYOC Tweed Royal kit amp; Homebuilt 1.5W Firefly Head; Epiphone Valve Jr. combo + mods; Drive 2x12 cab / Celestion G12M Greenback + G12H30; AB Custom Audio 1x12 cab / Celestion Alnico Blue

    Pedals/Effects - ZILLIONS, including DVM's Home-built Pedals - See some HERE and HERE, TOO!

    DVM's Gear Photos
    Visit MY WEBSITE!



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