Problem jcm2203.. OT?

[giordydiver]

Hi, I finish to build 2203 with 6550 and sir34 for a friend but a I have a problem. With no cabinet and guitar load if I turn on the amp OT make an hight strange sound i dont know why...I had 4 el34 and try this, no noise, nothing... What I do? Are the OT or the tubes?

[danman]

You should never run a tube amp without a load (speaker) or damage can occur to the OT. If this is a new build, and you are hearing a loud scream through the speaker when you turn on the amp, then you most likely need to swap the wires at pin 3 on each pair of tube sockets.

[giordydiver]

ok but why only wirh 6550 and not with el34?

[giordydiver]

so I swap wires and it's ok, no noise...now I have a question, load my guitar and no sound... if I turnup volume engrease the hum but no sound from my guitar...i check also the voltage, all ok but preamp tube have a plate voltage ok 408v...what I do?

[neikeel]

so I swap wires and it's ok, no noise...now I have a question, load my guitar and no sound... if I turnup volume engrease the hum but no sound from my guitar...i check also the voltage, all ok but preamp tube have a plate voltage ok 408v...what I do?

Check your wiring.

I echo danman. NEVER run a tube amp without a load, at best you will kill tubes, at worst kill the OT.

There is a mistake or dry joint somewhere. Where it is I cannot see from here

[giordydiver]

So, The wiring is ok, the problem was two resistor failed, now is ok great sound