Why K.F. did´nt double the 1st stage?

[hans-jörg]

Hi,
i´m wondering why K.F. rather wasted one triode instaed double the input stage. He should know that it would reduce noise, make the input stable and dont harms at all. Is it rearly so?
And as I read here, it raises the gain - do I want this? Is´nt it enough gain in an Liverpool, Express?
Did he ever done this "mod" on his circuit?
I know that we, in times as such they are, have to have a look at every triode.
Maybe at his glory times the best tubes lay around at the street, behind every corner, but we have to pay a high price today. Too much to waste a triode.
Is it this, or is it only a "Mod", one of many other mods. And not necessarily important for circuit. Should it be important for it, K.F.would done it, or not?

I already implemented the second (doubeling) Resistors at the board, but still hasitating to build it in with that (non K.F. conform) mod.
Please delight me.

Regards

Hans-Jörg

[Gee]

I had often thought about this too. I was reading the excellent Valve Wizards book recently, and he pointed out that when using a parralled input stage, the frequency response tails off rapidly when the guitar volume is turned down. Perhaps this is why KF didn't parallel up the first stage.

[Gibsonman63]

I paralleled the first stage in my Liverpool. I built it that way, so I didn't compare it to how it would have sounded otherwise, but I really like it. The amp is almost dead quiet, just a little hiss but not very much, then it roars to life as soon as you start playing. That much gain in one of my Marshalls would be humming like crazy. I don't know why more amp companies don't do this.

I am considering this on my Express now, along with some other tweaks. I haven't decided if I want to make it switchable or not yet.

[hans-jörg]

I had often thought about this too. I was reading the excellent Valve Wizards book recently, and he pointed out that when using a parralled input stage, the frequency response tails off rapidly when the guitar volume is turned down. Perhaps this is why KF didn't parallel up the first stage.

Hallo, thank you
I guess this was a main reason because the Wrecks should hang on the volume lige dogs on the ...

Gibsonman63
I built it too in my test versions of Express, K60 and K50 but I could not find much different in noise (maybe because my amp(s) was death quiet before and afterward. So no real evolution.

Regards

Hans-Jörg

[Clyde]

Some would say this is sacrilege and shouldn't be done. Once upon a time I'm sure that internal combustion engines were regarded by steam power proponents as heresy too. There was never a design that couldn't be improved upon and I think members of this forum are proving that to be true. Go for it.
I've been using the new TAD 7025's with great success as very quiet input tubes.

[katopan]

You can also halve the plate and cathode resistor values and double the cathode cap value on that stage and keep the normal level of gain and same cathode cap rolloff freq. Still the lower noise benefits.

[tweedeluxe]

My theory is that it's because the miller capacitance is doubled. The tone stack loads down the 1st stage enough to prevent loss of highs no matter where your guitar's volume control is set (because the gain is reduced, miller capacitance is reduced).

Parallel the input stage, and a 500k pot, depending on setting, may now bring that LPF corner freq down into the audible range.

The other reason that I suspect this may be the reason - why else would Ken not include a grid stopper on V1? Just a little more help keeping that input resistance as low as possible to reduce the chance of any guitar pot killing high-end.

I have tried it both ways, compensating for impedance, and I think I do prefer the single triode, though I don't detect any real difference in brightness. The parallel seems better at first, thicker etc, but there is a loss in the clean-to-mean quality of the amp that ruins it for me.

[Reeltarded]

You can also halve the plate and cathode resistor values and double the cathode cap value on that stage and keep the normal level of gain and same cathode cap rolloff freq. Still the lower noise benefits.

*This*

Keep on time constants and the trains arrive just the same.

[tweedeluxe]

. . . AND halve the value of the Rs in the tone stack and double the value of the Cs.

In my experience, even compensating as such, the clean-to-mean potential of the amp is reduced. less clean range

[leadfootdriver]

I've experimented with parallel triodes in another build. PT's give the tone a fatness that might not fly in an Express build. It leans more to the vintage side.

[Markusv]

Did it in my Liverpool

It may affect the clean to mean yes- but I enjoy the fatness it brings specifically in a el84 amp.

I am only a moderately good player anyway. A wreck is probably never going to be optimally used in my hands

The benefit of the paralleled stage for me is the lower noise floor
The amp is super quiet for the amount of gain on tap

Markus V