PI grid leaks

[iknowjohnny]

What exactly would the effect be of lowering the 1M grid leaks on a LTP PI down to say 470 or 220k?

[tubeswell]

at 470k - less crap noise mainly

But by the time you start getting down to 220k its more attenuation as well

[iknowjohnny]

You mean like the sizzle at the top or what? A cleaner more articulate distortion?

[ChrisM]

Less highs in my experience, fidelity kinda goes down the crapper too imo.

[Andy Le Blanc]

Your increasing feedback, between those and the tail.
Make both variable and play with it, a 100k pot. for the tail and a 1M dual
pot for the grid resistors.
I think I remember seeing a master volume there with a dual pot. too.

[iknowjohnny]

Your increasing feedback, between those and the tail.
Make both variable and play with it, a 100k pot. for the tail and a 1M dual
pot for the grid resistors.
I think I remember seeing a master volume there with a dual pot. too.

not a bad idea ! I may have a 2x1M pot too.

[iknowjohnny]

I tried paralleling 1M resistors with the 1m's that are there for 500k. Hmmm....i liked the results in some ways, but i prefer it overall with 1M. I also tried the tail and cathodes resistors. The cathode is very obviously best a a low value like the 470R thats there. But the tail seems to sound better at 47K then the 10k thats there. What exactly is that doing in technical terms? It sounds smoother and springier.

[David Root]

Lowering those resistors improves balance as well as reducing noise. Depending on what you're trying to do that may or may not be positive.

[Structo]

I did a master volume like mentioned above.

It is called a bootstrapped MV.

I used it on a little 6V6 push/pull amp.
Seemed to work the best on that amp among the ones I tried.

There are a couple variations of it.

[iknowjohnny]

i gotta try that. But does the tone change a lot a low vs high settings?

[Bob Reinhardt]

I tried the bootstrap master. I didnt like it at all. I guess for a high gain amp its probably good, but it didnt sound or feel "natural" to me, and it took away the presence "sizzle" in a marshall style amp.

[iknowjohnny]

Mine is a hih gain amp, so maybe i'll like it. Gotta see if i have that 1m dual pot still. One thing i'm not sure about tho is whether this will cause the PI to distort when set low. As i see it from my very limited knowledge, i think not. But if it does it won't work for me because i have tried a crossline master after the PI and when the PI distorts on this amp it's utterly horrible. It gets extremely thin and the distortion is that ratty horrible kind you'd get by overloading a recording console input. unusable at best.

[Andy Le Blanc]

you can set the bias to taste, the whole circuit is self balancing and very forgiving.
The larger the tail the more linear the response but it becomes a trade off with gain.
It solves issue's with tube drift and stability.

[iknowjohnny]

heres a related question. When my PI distorts, as i said it gets very nasty sounding. yet the amp from the cathode follower thru the stack and the PI is all exact marshall specs. What could cause that? using either a crossline of dual pot at the power tune grids gives me that nastiness, so we know it can't be the PA since it's after that. It only happens when the PI is hit with a big signal. the pre is cascaded so theres a lot of signal. But it's not by any means super hi gain and even at lower gain settings it will happen with a post PI master. The pre PI master i normally use is fine because i never turn up loud enough to get to that real nastiness. Voltages are around typivcal for all stages. What could cause this?

[Andy Le Blanc]

Thats come up before...... I cant remember the thread, structo might remember??? drhursly???