| Author | Message | ||
     Dustin Simons (dustin_the_wind) Username: dustin_the_wind Registered: 10-2006 |
Hi, I'd like to convert my 75 reverb head to el34 tubes to get more of that marshall crunch. Im wondering if this will work on my musicman: 1. Replace the 470 ohm resistor that's between pins 4 and 6 of each output tube socket with a 1000 ohm, 2 watt resistor. 2. Disconnect pin 1 only of the 1500ohm resistor that's between pins 1 and 5 of each output tube socket. 3. Disconnect the wires on pin 1 of the output tube socket. 4. Reconnect the wires that were on pin 1, to the end of the 1500-ohm resisors that are now standing free on each output tube socket. 5. Connect pin 1 to pin 8 of each output tube socket with a solid wire. 6. Increase the value of the resistor that's in series with the bias diode to reduce the bias voltage until you obtain proper bias. The great thing about this mod is that you can switch between 6l6 and el34 just by rebiasing afterwards. Thanks! | ||
| Edward Solberg (edward_solberg) Username: edward_solberg Registered: 05-2006 |
dustin, I have never had a 75-watt, 6l6 model amp on my bench but the wiring scheme you proposed for el34 socket seems all wrong to me. pins one and two are bussed together for termination of all ground conductors and ties to the suppressor grid. that ground is tied to pin eight (the cathode) via a 10 ohm resistor. pin three is the 725 vdc plate leg with a 4700 pF cap tied to pin 2. pin four is the grid tied to the large 10 watt, 1.5 K carbon comp resistor--this is the final destination of the 360 vdc (reduced by the CC resistor) coming from source "g." pin five is tied to a 1.5 K resistor carrying the signal from the driver (the resistor is tied between pins five and six with the signal coming in on pin 6). pin two (of the grounded pair) is for the heater ground wire and pin seven for the positive feeder of the heater circuit pair. and we're back to pin eight--the cathode. you'll have to verify this information against the schematic for your model (especially if it has the solid state driver--mine uses a tube and cathodyne phase inversion for the driver, I believe the ss amps are quite different in this regard). You'll also want to verify the information against a schematic of an el34 tube. my only experience is with 65-watt and 130-watt amps WITH the 12ax7 driver tube. SO PLEASE CHECK YOUR OWN SCHEMATIC BEFORE FOLLOWING THE INFORMATION I'VE GIVEN HERE. and for God's sake, IF YOU'RE NOT QUALIFIED TO WORK ON THESE BEASTS, HAVE SOMEONE WHO IS DO THE WORK. THERE ARE 725 VOLT DRAGONS LURKING INSIDE AND THEY WILL SLAY YOUR ASS IF NOT CAREFUL. (don't be offended if you are more qualified than I, safety concerns require that I give the above caution.) and last, if you're looking for "marshall-crunch" in a musicman amp, I think you're pursuing a phantom. any sort of crunch at all occurs at very high volumes on these amps that are best known for their "clean" at high volume. if you're into using pedals, high volume clean tone or playing jazz you can't beat these amps. but, you will not find a plexi secretly hiding within a musicman amp without a considerable amount of modification....for that, you'll want to contact terry loose or ed goforth. good luck with your mod, ed s. |