non-HRM Findings

[greiswig]

Make the change and let the voltages fall where they may. The 100K plate will be higher and looking at my notes, the last time I did this I had 205 on CL1 and 189 on CL2, 194 and 198 on V2.

Thanks, heisthl. Okay, because this is an amp builders forum, and because I'm the kind of a guy who likes to understand the "why" behind things, can someone edumacate me on this?

Is the value of the plate resistors on a stage driven by the desired voltage on that stage, or is the Pr value driven by some other goal (gain, etc.) and the voltage should be treated independently of the Pr value to some extent?

[heisthl]

The plate values are mostly a gain/feel/tone thing - Fenders used 100k with 1k5 @25uf most modern clones use 220k with 3k3 and 150K with 2k2 @5uf. just try the different values and listen - You can use 20 minutes doing formulas or change the values in 5 minutes and play for the other 15 minutes and hear it in real time. Then we can ask you

[Zippy]

Fender was using lower dropping string voltages with the 100k plate resistors - well, actually, they just used 100k plate resistors on pretty much everything regardless of dropping string voltages. Tweed Super ran 140V on plates, brownface Vibroluxes ran 180V, and blackface AB763 Twins ran circa 240-260V - all with 100k plate resistors.

I noticed just today that when members speak of using 220k plate resistors and achieving a "browner" sound, they are keeping the dropping string voltages the same, hence, lower voltages at the plates. 100k plate resistors with the same dropping string values (higher plate voltages) will give a stiffer feel and brighter sound. No surprises.

[greiswig]

(SNIP)
I noticed just today that when members speak of using 220k plate resistors and achieving a "browner" sound, they are keeping the dropping string voltages the same, hence, lower voltages at the plates. 100k plate resistors with the same dropping string values (higher plate voltages) will give a stiffer feel and brighter sound. No surprises.

Thanks again, all. So if you change from 220k plates to 100k plates, but you *do* change the dropping string to bring the voltage back down to 190V, what would you expect the effect to be?

[heisthl]

Thanks again, all. So if you change from 220k plates to 100k plates, but you *do* change the dropping string to bring the voltage back down to 190V, what would you expect the effect to be?

I would expect the effect to be what you hear when you try it

[dogears]

Zippy, I have not noticed much of a change in plate voltage when changing the plate resistors, as long as I maintain the plate/cathode resistor ratio of 66 to 1. Ie, 100k/1.5K and 220k/3.3K

Fender was using lower dropping string voltages with the 100k plate resistors - well, actually, they just used 100k plate resistors on pretty much everything regardless of dropping string voltages. Tweed Super ran 140V on plates, brownface Vibroluxes ran 180V, and blackface AB763 Twins ran circa 240-260V - all with 100k plate resistors.

I noticed just today that when members speak of using 220k plate resistors and achieving a "browner" sound, they are keeping the dropping string voltages the same, hence, lower voltages at the plates. 100k plate resistors with the same dropping string values (higher plate voltages) will give a stiffer feel and brighter sound. No surprises.

[greiswig]

Thanks again, all. So if you change from 220k plates to 100k plates, but you *do* change the dropping string to bring the voltage back down to 190V, what would you expect the effect to be?

I would expect the effect to be what you hear when you try it

Ya know, it's okay to just say "I have no idea what to expect."

[heisthl]

I do know what to expect - I've done it many times but YMMV. Try it, you might like it.

[Zippy]

Zippy, I have not noticed much of a change in plate voltage when changing the plate resistors, as long as I maintain the plate/cathode resistor ratio of 66 to 1. Ie, 100k/1.5K and 220k/3.3K

Thanks, Dogears.

[greiswig]

Zippy, I have not noticed much of a change in plate voltage when changing the plate resistors, as long as I maintain the plate/cathode resistor ratio of 66 to 1. Ie, 100k/1.5K and 220k/3.3K

Thanks, Dogears.

This is interesting. I noticed about 8V rise on V1a when I went from 220k to 100k with the correct cathode values. When I also changed the V2 values, voltages changed again throughout the preamp plates. That's why I asked the question about bringing voltages "back into line" by revisiting the dropping string. Clearly heisthl does not think that there is much of an effect of changes like that, but given my initial experience of having the tone improve noticeably when I got V1 around 190 and V2 around 200, I thought it might have an effect.

[ayan]

Zippy, I have not noticed much of a change in plate voltage when changing the plate resistors, as long as I maintain the plate/cathode resistor ratio of 66 to 1. Ie, 100k/1.5K and 220k/3.3K

Thanks, Dogears.

This is interesting. I noticed about 8V rise on V1a when I went from 220k to 100k with the correct cathode values. When I also changed the V2 values, voltages changed again throughout the preamp plates. That's why I asked the question about bringing voltages "back into line" by revisiting the dropping string. Clearly heisthl does not think that there is much of an effect of changes like that, but given my initial experience of having the tone improve noticeably when I got V1 around 190 and V2 around 200, I thought it might have an effect.

You are correct. Lowering the plate load rersistor will definitely increase the plate voltages, all other things remaining equal.

Gil

[heisthl]

This is interesting. I noticed about 8V rise on V1a when I went from 220k to 100k with the correct cathode values. When I also changed the V2 values, voltages changed again throughout the preamp plates. That's why I asked the question about bringing voltages "back into line" by revisiting the dropping string. Clearly heisthl does not think that there is much of an effect of changes like that, but given my initial experience of having the tone improve noticeably when I got V1 around 190 and V2 around 200, I thought it might have an effect.

What? I've always been a big advocate of preamp plate voltage importance. Learning the hard way that 200 is not a magic number on CL1. It absolutely depends on the amp on your bench where the sweet spot will lie and the 180-200 is just a "rule of thumb". As to the 100k plates I was suggesting you try them with no changes because that voltage is close enough to tell if you like the 100k Gain/tone/feel and if you do you treat it just like you did before and tweak voltages by playing with tube selection or dropping string values to get the last 5% of great tone. I think my standard rule of lower=smoother (to a point) applies but is not essential to just see if you like the sound of 100K plates in your amp.

[dogears]

Yep... I did mention much of a change The current draw changes a little so this much explained. However, the amount, as noted, maybe less than 10V doesn't account for much of the tone differences.

Thanks, Dogears.

This is interesting. I noticed about 8V rise on V1a when I went from 220k to 100k with the correct cathode values. When I also changed the V2 values, voltages changed again throughout the preamp plates. That's why I asked the question about bringing voltages "back into line" by revisiting the dropping string. Clearly heisthl does not think that there is much of an effect of changes like that, but given my initial experience of having the tone improve noticeably when I got V1 around 190 and V2 around 200, I thought it might have an effect.

You are correct. Lowering the plate load rersistor will definitely increase the plate voltages, all other things remaining equal.

Gil

[ayan]

Yep... I did mention much of a change The current draw changes a little so this much explained. However, the amount, as noted, maybe less than 10V doesn't account for much of the tone differences.

If the voltage source (B+) is the same and doubling the size of the plate load changes the plate voltage "only a little," what is making that possible? The fact that the plate current must be changing "a lot." What say you? I am just saying.

Gil

[greiswig]

What? I've always been a big advocate of preamp plate voltage importance. Learning the hard way that 200 is not a magic number on CL1. It absolutely depends on the amp on your bench where the sweet spot will lie and the 180-200 is just a "rule of thumb". As to the 100k plates I was suggesting you try them with no changes because that voltage is close enough to tell if you like the 100k Gain/tone/feel and if you do you treat it just like you did before and tweak voltages by playing with tube selection or dropping string values to get the last 5% of great tone. I think my standard rule of lower=smoother (to a point) applies but is not essential to just see if you like the sound of 100K plates in your amp.

Okay, I've tried it. I also know "trust your ears" is the rule o' the day here. But for those of us who doubt our own abilities in assessing differences that experienced amp builders could readily hear *and* explain, I'd appreciate some input.

I like the cleans quite a bit better with lower plates. But even with 220/150 plates on the OD tube, I seem to lose a bit of the definition in overdrive with the lower CL plates. This seems most noticeable when the OD gain is set fairly low, when you're just trying to put a little hair on the notes without full-on distortion. Is that in keeping with other's experience?

I also think I remember some similarity between low plate cleans with 44M/.05 LNFB and higher plate cleans without LNFB. However, this is not based on direct A/B comparison. If this were true, it might enable the "best of both worlds" approach since one could switch the LNFB on and off. Does that similarity ring any bells for anyone else?