dumb tube amp question...

[SteveB]

its always assumed it seems that V1 is the "most important" preamp tube. On a cascading high gain preamp though, isn't the tube following V1 the one getting pushed into overdrive and therefore important for the character of it's distortion?

[Kurt L]

I'm not an expert - but I think the answer is that whatever comes out of the first tube gets boosted every step of the way. Any problem with V1 gets magnified along with the signal.

[SteveB]

I guess I wonder how much distortion actually happens in V1. I would expect most tubes to at least sound "decent" in their normal operating range, but their distortion characteristics might vary widely.

[ArnieZ]

This is what makes it so hard to make an amp with cascading gain stages. If you distort V1 with too much signal than the next stage gets overloaded and amplifies a clipped signal and distorts itself and sends it on down the line. The result is a fizzy sounding tone with poor harmonic content. Preamp tubes have a tonal signature in both the clean and overdriven modes. There are tubes that will work better in some stages than in others. What they are I don't have a clue. I have never played a cascading gain amp that suited me, although there are lot's of guys that make them sound great!

ArnieZ

[tbonesullivan]

One thing that people have glossed over: preamp tubes are dual triode valves. So, that first tube can be the first AND second gain stage of a cascading gain chain. It depends on how the amp was designed. V1 is closest to the input and is the input driver. In some amps one triode is the clean input driver and one the gain channel input driver. In others the first triode is the input driver for all channels and the second is the first gain stage of the gain channels.

Be aware however that it's also possible that the second triode can be other things as well. The only way to know for sure is to consult schematics.

But as said, V1 is the first tube to see your signal. All other tubes amplify what this tube does. If you have one "BIG MONEY" tube (Mullard, Telefunken, JAN Philips, Tung Sol Reissue, etc) this is where it goes. Another thing to consider is whether your amp has DC or AC filament heaters. If they have AC, like a lot of older amps do, you may want to consider a spiral filament tube like the Sovtek LPS, as this will cancel out the interference.

Other things to consider are whether you have a combo or a head + cabinet amplifier. Tubes with longer plate structures are more prone to microphonics.