Aiken is a bright and generous person to post this great info so freely, and in such excellent and clearly written form.
Aiken's excellent paper on triode preamp biasing to gain understanding, here: Yes, guitar preamps are biased, Yes, you can adjust it.should you? probably not in this case. See schematic for these, check or take it to a tech. Grid stopper resistor noise at: R8, R13, R32 Grid leak resistor failing or cold solder joint at: R12 or R24ģ. Other potential non-tube "hiss" sources in class A preamp designsġ. Jiggle, clean, or reset all those jumper connectors you see in the schematic, or take it to a tech.or That's the cost of all those cool features, switches and knobs. Unfortunately, there are lots of places for things to go wrong in this design. If still noisy after swapping tubes per above, and maybe swapping in a couple known good alternates in each position, then perhaps circuit component failure or perhaps a problem further down the line. Read here to glimpse why it is not wise to push heater / kathode voltages too much in a preamp triode. If V3/4 are getting abused, they too will eventually fail. Ex., 12ax7 kathode to filament max is 180v (an optimistic figure for modern preamp tubes, by the way!) complicated amps with effects loops or other elevated cathode voltages are particularly suspect.like maybe the Rebel 30? :-/ It is entirely possible that a 12ax7 whose heater kathode insulation is perforated by abuse will run perfectly quietly in V1 or V2 of your amp.but don't relax.because your Rebellious 30 may be busy eating the insulation of the 12Ax7 you swapped into V3/4! :-/ This is because they run certain voltages very near or in excess of the typical 12AX7 in design limits, like V3/4 in your Rebel. Some amplifiers are particularly hard on preamplifier tubes. Re: lf tube swap "cures" noise, and Rebel 30 ate my tube, why V3/V4? Why wasn't it V1? Well, it MIGHT have been V1/2, but after looking at the schematic, I dunno. Quick look at the schematic V3 and v4 appear to be operating in a way that would put the tubes in them at a little risk due to somewhat elevated heater to kathode voltages. (Yes, V3) Does noise seem to "disappear"? If yes, V3 (!) tube may be bad. Unfortunately, the Rebel 30 is a complicated little devil. After checking what RobRob mentioned in the post immediately above mine, read on.
0 kommentar(er)
