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Hi so i just bought Bugera G20 used, guy said that tubes need to be changed, so i changed power tubes 2x el34, before there was no sound at all coming out from the amp, now there is on clean channel but on overdrive nothing, when after 2 mins on clean front standby light start to flash and 2x infinium at the back. when it comes to pre amp tubes one of them is not light up at all, so i swap them to see if this one is broken, but in another place it was fine, basically one in front is never light up. what could it be ?
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Could be a cracked solder joint on the tube socket. These are PCB mounted sockets so that is not uncommon. If a known good tube "isn't lighting up at all" it means the heater is not getting voltage. Assuming this is 12AX7 the heater pins are 4 and 5 with pin 9 being a center tap of the heater. It should have 6 volts AC or DC between pins 4 and 9 and also between 5 and 9. Sometimes pin 9 is grounded but sometimes it floats and they put 12 volts AC or DC across 4 and 5.
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