How does pulling a not needed tube affect the amp?

[RockinRocket]

I tried this in my 18 watter I pulled one channels tube and measured the volts. The PI went up around 10 volts and the preamp of the other channel around 8 volts. Now Im wondering what else is going on. Did I effetively reduce how the filter cap charge/ tube rectifier sag, now their is less pre amp tubes to supply or does it not have an effect because the other channel isn't being played through? If so would reducing the filter caps value help bring back the amp filtering/ response to normal for the less tubes?

I'm interested in the theory because I played the amp both ways and may not of heard much difference but am really interested in what has happened in side the amp. Thanks

[Leo_Gnardo]

In the example you give the answer is what you heard: not much. In typical 2 channel Fender amps (and those similar) I'll sometimes recommend the user remove the pre tube of the channel that's not being used to minimize the noise sent out of the unused channel's second triode. Typically it's the "normal" channel 12AX7 that's being removed.

Yes the voltage at the preamp supply node rises a couple of volts because no current is being drawn by the now missing tube stages. This may result in the remaining pre sounding just a tiny bit brighter & tighter, hardly enough to notice.

[RockinRocket]

Thanks for the insight Leo.

Will the amps power supply sag as normal with out the other preamp tube? All its doing is eating 8 volts when I'm not using that channel. Wondering from a text book point of view if the amp will sag and the dynamics be the same.

In one experiment I pulled the unused tube and grounded that channels PI coupling cap. I thought doing that will give a 3db gain increase. I didn't notice the difference but I may try it on a switch once I buy one. Is 3dbs basically nothing ad is my understanding of this accurate?

[Stevem]

Oreamp tubes pull less than .02 ma from the power supply so thinking about if sag is changing is just wasting time!
What will change a tad is the heater voltage to the other tubes, but not enought to make a difference unless you have a very weak preamp tube.

[RockinRocket]

Heater Volts Ill measure those. That cant effect tone anyway right unless really extreme?

Edit- I checked the heater volts they measure 3.2 with either 2 or 3 preamp tubes.