need help - repair amps

[fibredrive]

hi all,

asking on behalf of my cousin, he's got a 30th Anniv Marshall JCM900 amp. not working anymore, wondering who can repair it and any idea how much? or is it just simple case of replacing the tubes? how does one find out whats wrong with the thing?

cheers

 

[Viruz]

Go Davis guitar to repair..U never state wats the problem of e amp?

 

[fibredrive]

hiya, the prob is with a loud high pitched screech when the amp is switched on. sorry for not stating earlier. is it a tube change thing? or worst?

 

[p00n]

My guess would be that its due to microphonic tubes. When did he last have a tube change?

 

[Viruz]

Sound tat way.If the JCM900 have tat standby switch,use it.Try switch main on first and put the stdby switch in off position for abt 30secs.Let the tubes warmup first.Then switch on.See wat happens.Preamp tubes should be no problem for u to change.But power tubes will need extra attention from amp tech.Hope this help.

 

[fibredrive]

thanks guys. will try out the solutions. the last time he played the thing was almost...2 years ago...!

 

[hay88]

mikeman does amp repairs

 

[fibredrive]

yeah he pm-ed me. sent the contact to my cuz liaoz...cheers

 

[Timex]

2 years is about right for a tube change. I suggest u check out the 12ax7 tubes first. If it were a power tube prob, the LED on the rear panel will light or the fuse will blow. Hope this helps.