Tube Amp Archive

the volume pot problem is solved. it was a bad solder joint on the ground leg of the pot. buying tubes, caps etc are time consuming in Turkey so i will wait for a couple of weeks until they arrive. thanks for the support. i hope to have your support back again when the parts arrive.

another problem started before solving the previous one. i started hearing a "pop" sound from channel B. i swapped the tubes of that channel with channel A. the "pop" sound started at channelA. i have only old tubes available so i swapped the tubes with an old set but one tube made an arc inside if ...

i will replace the caps but it is hard for me to find them here in Turkey. i need to order them via internet. do i also need to change the big filter caps?

installed 47K trimmers, dialed them around 14K and the redplating stopped. the readings didnt alter much, they are still above the specs for EL84's but no visible redplating. next question is, when i swap the JJ 12ax7 PI's with Mullard 4024 tubes, V5 and V6 start to redplate again. voltage readings ...

I don't think you can really protect yourself from a pot failure. I think I would just replace the 33k with the 47k trimmer wired as a variable resistor, i.e. with the wiper shorted to one end of the element. ok, this means less work for me. i dont know much about the technical side of tube amps bu...

do you think a 15K resistor and a 47K trimmer is suitable for this job? i will use a 15K to keep things safe in case that the trimmer fails.

Leo_Gnardo wrote:Why am I not surprised?

I'd alter the bias supply so you can dial it up to @ -14V.

ok, it is getting clear now. i need to have a trimmer in place of the 33K's so that i will try to dial pin#2 voltage to -14V.

You could try to dial the power tube bias down by decreasing the value of the 33k resistor at bias supply node E, but I don't know if there is enough room to work. You could clip a pot across it and give it a try. Otherwise you'd have to lower the two 330k's on the other side of node E. those 330k'...

yes, i swapped the PI's with mullard cv4024's. i think they made it worse. is it normal that when there is no PI inserted in the circuit, the redplating stops?

"I'd alter the bias supply so you can dial it up to @ -14V. " i have no idea how to do this?

here is my tube swapping adventure; i have changed the place of the redplating tube ( it was ch.A) and the same tube redplated again in its new socket. i have changed the redplating tube with a new JJ EL84 from my “never touched” set. The new tube redplated in the same socket. i have changed all the...

hi, i am the owner of the mesaboogie 2020 amp for more than 13 years. the problem is , all (4) tubes are redplating. here are some readings; pin#7: 390V pin#2: -11.2V pin#3: 13mV pin#4, pin#5: 3.5VAC pin#9: 330V i have used "this method" to measure the plate currents. "The plate current can also be ...