This is why I'm looking to add to it's design the functionality of a typical jumpered 4-input/2-channel amp like a 5E3 or Marshall style amp, but with each channel having two parallel triodes. I'm thinking that for full effect, I may need to split the cathodes of the two tubes and that will open a whole new round of calculations and testing.
You can build it that way, but like PRR and I said, the functionality of the design was so more players/singers could use the same amp. Amps were expensive and everybody, especially young bands, couldn't afford their own amp.
The Marshall thing was a design flaw, that turned out to be a happy accident.
Their will be possible pluses and definite minuses in doing a 4 x || triode input. You'll have to weigh them out to see if there's an overall benefit to what you want to do.
Amps are designed to take a very small input signal and amplify it with in reason, as much as they can, to protect that small input signal from noise and instability problems. Input stages are the most sensitive because the signal is so small. What ever noise gets amplified along with the input signal in that 1st gain stage, will be amplified by every gain stage after. Each gain stage amplifies
anything that's injected into that tubes grid
and any hiss from that stages R's and from that tubes heater. But each stage after the signal is much larger than the noise/hiss/heaters, so that it swamps out them out.
A few builders do use a || input stage. Probably to get a little more gain and use up the extra triode they're other wise not using in that amp. There are some benefits to || 2 triodes.
I think you'll get a lot more signal to noise (s/n) noise from 4 triodes instead of 1 and the added noise penalty of 4 triodes having to amplify the very low guitar pick ups (PUP's) output, and the noise from amplifying 4 separate triode heaters instead of 1. And you will have extra grid wire with very small signal on them, could be a problem for noise and/or instability. (You might be able to/might have to use shielded wire to fix any problems there.)
You'll have more noise from more plate R's, more cathode (K) R's, and more grid R's. I don't know if you could get away with using a single plate/K/grid R on 4 triodes? Wiring might be a mess and cause problems? A set of R's for each tube might be fine.
Extra space, 2 tube sockets instead of 1, more board space, you could do 1 (or 2) jacks instead of 4. Maybe a front panel switch?
With 4 triodes in || the gain
will slam the next triodes grid, causing blocking distortion, very unpleasant sounding. You will have to cut that signal down with a voltage divider before the next grid and a large grid stopper. But it can be done. Using a low gain triode like a 12AU7 would also help a lot. But it still might be too much gain without a voltage divider before the next grid and use a large grid stopper? But the R values in the voltage divider and grid stopper would be smaller.
You can try it but you'll need a 4 input amp with 2x tubes/4x triodes at the input. Most all 4x input jack amps only have 1 input tube. You could just try 2x || input triodes to hear if you think it's better, going in the right direction sound wise?
If you want more gain or a fatter, fuller, beefier sound, there's other ways to do that without the noise and possible stability problems.
A single || input tube with a couple/few other mods might be likeable to you? Would probably get you out of some possible/probable noise/stability problems.
Topic: Please Help Me Understand? (Read 4854 times)