Has anyone played around with lower Rp values on a 12AX7?

[stephenl]

Randall Aiken recommended operating a 12AT7 with 47k / 1k5 / .1u in V1 - apparently that's what he used in his TomCat amp. I tried it and it sounded really nice in the V1 of a K50ish circuit. I rolled in a new production Mullard and TungSol 12AX7 with those values and liked it even better. Very smooth and chimey.

I'm curious if anyone has tried any thing similar and what you thought of it.

[roberto]

Yes, down to 33k, but it that case was a third stage of a four stage lead channel. Of course is not possible to give general indications on low plate resistors (with which Rk? Which voltage? Which load? Blabla).

Generally speaking, I've noticed less high order harmonics.
I use lower Rp on amps like Engl to add clarity to the sound and to permit a better handling of detuned guitars. It works good also with an high plate stage just after it.

[Stevem]

If you pull up the RCA tube manual then near the back you will find a chart that will cover all of your questions in full!

[tonewood]

If you pull up the RCA tube manual then near the back you will find a chart that will cover all of your questions in full!

Heck, then I guess we don't even need this forum. Well, I do use the tube manual frequently but I still really enjoy hearing other opinions when it comes to the sound of a circuit. stephenl- thanks for your take, it makes me want to give it a try.

[Reeltarded]

I don't think he meant for you to take a hike..

This forum needs the RCA manual.

[matt h]

(deleted)

[Stevem]

Sorry, I did not mean to take a hike, nor that the rca book covered tone,just that it stated the resistor values, power supply voltage and signal voltage gain for a good amount of these variations !

[Phil_S]

I'm pretty sure I've posted this before. Maybe it needs to go into the sticky for reading material?

[Stevem]

Yop, that's her!

[stephenl]

Thanks for the comments. I have perused RDH and used LTSpice to simulate different operating points which gives insight as to how the stage might perform not so much as how it will sound comparatively. I was just looking for general comments as to people's experiences, such as Roberto's. The majority of the circuits we see in guitar amps use one of several standard setups.

[jazbo8]

Did you find any correlation between the various operating conditions and the sound/tone as described by some (which are purely subjective in any case)?

[tubeswell]

I've used 47k plate resistor on 12AX7 stage. Makes the stage cleaner, which helps with jazzy tones.

[matt h]

(deleted)

[Tone Lover]

I've used 47k plate resistor on 12AX7 stage. Makes the stage cleaner, which helps with jazzy tones.

It's nice when theory and practice come together. I was thinking about this, primarily about "jazzy" (vs just clean). When I think jazz cleans, I think thick, round cleans... using a lower value plate resistor should tip the balance into more even-order harmonic content.

Sorta like how going the opposite direction does the opposite thing, giving those "liquid"/"glassy" lead tones--useful for input higher gain preamps (not just because it boosts the gain, and therefore the clipping...) but to keep clarity in later stages.

I was just going to say in valve wizards pre amp book he said taking it down to 47K brought more even order harmonics.
Bill

[JoeCon]

This leads me to ask has anyone tried a multi plate resisitor switch ala the impedance selector?? A heavy switch that would let you got from 220K to 100K to 47K to dial in the input??
Wouldn't this let you set your amp for like a jazz gig or a country gig or a rock gig by changing that first stage?
Anyone????