Recent content by Guitar Amp Tools

  1. Guitar Amp Tools

    Power Tube Grid Mute Switch

    Move the switch and place it between where the two cathodes (pin 8) on the power tubes are wired together and the power amp ground. When you open or close the switch it takes a second for the cathodes to charge/discharge and you get a soft ramp up and down and no thump at all. When the cathode...
  2. Guitar Amp Tools


    Listen to DonP, it's for a single EL84 amplifier. It will work in any EL84 amp plus enough current for at least 3 12AX7's. The drawing shows it is for a full-wave bridge rectifier so the 245 Vac listed on the schematic is only going to be about 65% of that after it's rectified to DC, around...
  3. Guitar Amp Tools

    Fuse keeps blowing in my TSL, anyone else have this issue?

    Does it still blow the fuse when you pull the output tubes?
  4. Guitar Amp Tools

    6550s in a SV20?

    No, you can't just drop in the 6550's, for several reasons. It is a cathode biased circuit, like the other guy said, which is self-biasing. So when the 6550's bias themselves it will be around ~70 watts instead of ~50 watts for the EL34's. The impedance of the output transformer is ~1.5k for...
  5. Guitar Amp Tools

    DSL100hr bias big problems

    Pull all of them, then check the voltages of pins 3, 4 and 5 to ground. Counter-clockwise looking into the socket
  6. Guitar Amp Tools

    Burnt diodes?

    Those diodes are there to limit any signal causing a voltage drop across R61 that is more than +/- .5 volts. Since R61 is only 10 ohms it must have been a big signal to cause that kind of drop like someone plugged a speaker output into the instrument input, like the guys suggest. What are your...
  7. Guitar Amp Tools

    Only one tube in 2203 working

    I always unplug the amp, leave the power switch and stby in the "on" position and let the amp sit for 5 minutes. Then discharge the power supply through a resistor and check for voltages from each pins of the power tube socket to the chassis. If everything looks good I jam a screwdriver across...
  8. Guitar Amp Tools

    DSL100hr bias big problems

    What are the power tube voltages with no tubes in the amp?