Ghost sound on my ac30. (seeking retube advice)

[RedOrangeMorning]

So, Greg, how difficult was it getting into the back of the amp to switch them out? I'm planning to change the tubes in my ac30 soon and I've heard it can be a pain in the ass due to the speaker wires being soldered and the tubes themselves being placed in an awkward area. Care to pass on your newfound wisdom?

Thanks,
Ryan

[Gw10101]

Honestly Ryan, it wasn't to bad, i removed the back plate (i think it was 8 screws)  and then there is an RCA pair that un hooks easily for the reverb tank leads. Then there is a quarter inch jack for the speakers that simply unplugs. following that there are 6 more bolts attaching the "head" part of the combo to the rest of the cabinet. once those screws are un done the tricky part is pulling the electronics out of the cavity. the poor part of the design is that the RCA female plugs stick down about half an inch below the rest of the carrage that the electronics sit in. so you have to kind of angle the thing out and up in order to get it free from the cabinet. and naturally the tubes are all located on the front so you have to remove the electronic "head" portion completely to replace the el84's, the 12ax7's you can remove  and replace without haveing to completely remove the electronics.

i hope the terms i used here give you an idea of what im talking abouit. im not sure about any technical terms.  but yeah, the hard part is finding all the screws the remove the electronics, and then the weird angles you have to use to get it in and out. out side of that it wasn't too bad

greg

[james_rock]

greg, you might make sure the power tubes don't need to be rebiased. i thought only the preamp tubes could be swapped without a rebi.

Vox's and most true class a amps (vox's are beleived to be class a/b) are cathode biased which means they bias themselves although i think this can be adjusted (by an amp tech) because they can still be slightly out

[star0nfire]

By the way, I think nobody mentioned it, but a good way to check whether you have Microphonic Tubes or not, and discover which tube is it, is to turn your amp to max volume, with nothing in the inputs of the amp, and slightly tap the tubes, one by one, with a pencil. If you hear any of them pop, you have a microphonic tube