The 6L6GC tubes were working before the mods, I also replaced them for a fesh pair of new working 6L6 GC and there's still no cathode current reading or output sound. Leaky/shorted from the driver tube plate to the power. In any amplifier: If the output tubes have just been replaced with new ones, 'infant mortality'/early dying of the new tubes. All of them involve the grid not being held at a negative enough voltage with respect to the cathode. The device works properly as Im able to use it perfectly with other amps, also used it with this amp before. There are relatively few causes of output tube bias problems. I'm using this device to measure the Cathode Current: ![]() Tubes Light up and the plate voltage is 497V. Also the theres no output sound going to the speaker. The amplifier was working before this mods,īut now although I have negative bias voltage I cant measure any Cathode current on the 6L6 tubes, it reads zero current. Categories Recent Repairs Tags dj equipment repair. I do have plenty of experience with tube guitar amps, and have serviced a few tube hifi. Messing around with the sockets could cause a more complex problem, and the potential to send the amp in for servicing, and replacement of the sockets. The stock schematic of the amplifier is here: If you have a smoke machine repair for me, please get in touch. The sockets should not be dirty, as your amp is a relatively new model, and the tubes have been in place. ![]() I schematic of the Bias supply circuit with these mods is attached, new resistor values in RED. I used an CTS 10K bias Pot, and adjusted the resistor values on the circuit so that I got a voltage range with the Bias pot from -44V to -58VDC Randall Ball is a musician and the owner of Ball Amplification in Kerneysville, W.Va., and he joins us now to. ![]() I'm modifying my tube guitar amplifier with an adjustable Bias Pot instead of having fixed resistor values. WARNING: A tube amplifier chassis contains lethal high voltage even when unplugged-sometimes over 700 volts AC and 500 volts DC.If you have not been trained to work with high voltage then have an amp technician service your amp. And bad news for guitar fiends - theres a problem with the valve amp supply chain.
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