Does low plate = low gain/distortion on tap?

[jcsifu]

As some of you that helped me trouble shoot a switching issue are aware, I just switched my high plate clone resistors to low plates. I swapped out the V1A + B bypass caps to 10uf as well, but left the trim pot and resistor the same as they were (220k and 100k pot). I had too much compression and distortion when it was a high plate and wanted to be able to have better dynamic control of the break up. Now after the swap I am finding that I have to turn the trim pot all the way up to get the rich harmonic tone I like from a D-style amp. Is this normal?

I am thinking that if I switched to the higher value trim pot it would make a hotter signal and maybe that is what I need. I would parallel a 1.2m resistor on a 500k pot for the 350k value.

Or...

What if I switch the od values back to high plate but leave the low plates on V1. Has anyone ever done this?

[marcos]

Weird. It is normal that you have to turn up the OD trim a bit (1.5 - 2 times
the setting you like with high plates) when changing to low plates,
but there should be plenty of range to get a good OD tone.
IIRC it has been reported that HAD adjusted the trim pot in low plate amps to about 50K to ground, maybe you could use this a starting point.
I suspect something else is wrong,
my 2 cents

Marcos

[jcsifu]

Weird. It is normal that you have to turn up the OD trim a bit (1.5 - 2 times
the setting you like with high plates) when changing to low plates,
but there should be plenty of range to get a good OD tone.
IIRC it has been reported that HAD adjusted the trim pot in low plate amps to about 50K to ground, maybe you could use this a starting point.
I suspect something else is wrong,
my 2 cents

Marcos

Hi Marcos,
I'm currently having to run the trim pot wide open to get a good OD sound. I have Clean Volume at #6 and ratio at #7. I have not tried this amp at gig volume yet, everything always sounds more like itself at higher volume. I have no free time at practice space as we are working out new material/show and this group is hard rock so I take my JVM410 and cab, which are full capacity for my car. I'm looking to sneak the amp in one day, so maybe I will rent an SUV so I can pack everything in it.

I still think that maybe changing the OD entrance to match the 124 values might do me a favor. What do you think?





.

[Kassie]

p in one day, so maybe I will rent an SUV so I can pack everything in it.

I still think that maybe changing the OD entrance to match the 124 values might do me a favor. What do you think?

Possibly, I have a 350k trimpot and run it at around 1/3rd to 1/2 at most. So that means definately 100k or more.

Did you also change the cathode resistors? And the level pot to 250K?

[jcsifu]

You know, I'm starting to wonder if because I've been playing a cranked Marshall I have gotten used to that and it has altered my hearing and playing enough that I just need to get used to the new sound and response of the low plate.

There is not much difference in the clarity and tone of both clean and OD, I can hear the added distortion to the chording stuff more than the single notes. It reminds me of my VibroKing when it gets cranked with a OCD pedal lifting it a little.

There was way more harmonic thickness in this amp when it was high plate.

Still might try switching the OD stages back to high. I'll wait and play it awhile as well as see what everyone else says about it before I do though. I would like the low plate to work for me.

[Kassie]

There was way more harmonic thickness in this amp when it was high plate.

Still might try switching the OD stages back to high. I'll wait and play it awhile as well as see what everyone else says about it before I do though. I would like the low plate to work for me.

Did you change the cathode resistors as well?
If you do the 124 mods, it will mean more gain on tap. I found the 124 version to have more thickness as well. Perhaps too much, it will get your dumble sound closer to a marshall then then let's say the 102 version. I also changed to 300UF filter caps. Now when I turn up the treble, turn down the bass and switch the mid cap out, I kinda have the same sound as the 102 version.

[jcsifu]

p in one day, so maybe I will rent an SUV so I can pack everything in it.

I still think that maybe changing the OD entrance to match the 124 values might do me a favor. What do you think?

Possibly, I have a 350k trimpot and run it at around 1/3rd to 1/2 at most. So that means definately 100k or more.

Did you also change the cathode resistors? And the level pot to 250K?

Hi Kassie,
I do have the 1k5//10uF on both V1 cathodes but I did not do the level pot. I totally forgot that one! I'm now thinking that if I swap the trim pot to 350k with 220k and the level to 250k I might have what I am looking for.

BTW, in case anyone is curious, my voltages are close enough to sound correct. I'm also using a les paul with 57 and 57+ pups, and a D-lator clone with a lexicon lpx-152. I have played with the levels of the Dlator return to get more gain too, but now I think you pointed me in the right direction.

[jcsifu]

I found the 124 version to have more thickness as well. Perhaps too much, it will get your dumble sound closer to a marshall then then let's say the 102 version. I also changed to 300UF filter caps. Now when I turn up the treble, turn down the bass and switch the mid cap out, I kinda have the same sound as the 102 version.

This sounds like what I want to get from this circuit. Bro, mine is apparently not right. I'll try the changes over the weekend, I should have the pots in my drawer. I'll keep reading this thread in the mean time to answer any more questions and to see what gets said.

[Kassie]

100k, 1.5k basically means hotter signal production in the preamp. More gain, but it's actually more amplification.. not necessarily more soft clipping distortion. Indeed the 100k pot must be maxed out I think. Try changing that to 250k/350K. The 250K level pot presents a different load to the 100k. Changing the timbre of the distortion somewhat. Attenuates more highs. The clean channal will be less fendery, It still produces nice cleans but you can get into the fat crunch territory more easily.

The 10UF's allow for more bass. I am still deciding wether I like that. Playing a les paul.. Might just go back to 5uf's. See how that goes. It's ok for a 1x12, but too much for a 2x12 Unless I turn the bass pot way down.

As always, tweak the amp without the dumbleator. It needs to sound good without.

[martin manning]

100k, 1.5k basically means hotter signal production in the preamp. More gain, but it's actually more amplification.. not necessarily more soft clipping distortion.

Maybe I'm missing your point here, but changing from high-plate to low-plate reduces the gain through the preamp, so the signal level going into the OD should be reduced. A logical conclusion might be that the OD entrance should be modified to get the required drive level, but I don't find that to be the case as I can get plenty of distortion from my 124-ish amp with the 220k into a 100k trimpot. The value of the OD entrance trimmer in the real 124 is unusual as far as I know.

[ToneMerc]

100k, 1.5k basically means hotter signal production in the preamp. More gain, but it's actually more amplification.. not necessarily more soft clipping distortion.

Maybe I'm missing your point here, but changing from high-plate to low-plate reduces the gain through the preamp, so the signal level going into the OD should be reduced. .

Correct Martin.

TM

[ToneMerc]

As some of you that helped me trouble shoot a switching issue are aware, I just switched my high plate clone resistors to low plates. I swapped out the V1A + B bypass caps to 10uf as well, but left the trim pot and resistor the same as they were (220k and 100k pot). I had too much compression and distortion when it was a high plate and wanted to be able to have better dynamic control of the break up. Now after the swap I am finding that I have to turn the trim pot all the way up to get the rich harmonic tone I like from a D-style amp. Is this normal?

I am thinking that if I switched to the higher value trim pot it would make a hotter signal and maybe that is what I need. I would parallel a 1.2m resistor on a 500k pot for the 350k value.

Or...

What if I switch the od values back to high plate but leave the low plates on V1. Has anyone ever done this?

Real low plates have the OD trimmer set differently, what you are experiencing is relatively normal.

I do have one quad 6v6 Amp setup with 150/120 into 100/100k. You could even try 150/120 into 150/120.



TM

[Kassie]

Ah ok then I was wrong, I should withold giving information without proper expertise.

I thought that lower cathode resistors (which bias the tube) set a higher gain. And I presumed that the 100K plates would allow for more current, but I simply do not know enough about it then. Does it have to do something with the different plate load? Back to study.

I do find that the low plate version has more lows/low mids then the high plate version. And the clean channel seems to break up earlier. But could my ears be wrong as well?

[talbany]

High plates have more gain and more headroom/swing (due to the larger voltage drop across the plate resistor,rails) and low plates have less gain and less headroom clip harder sooner..IMO it's really hard to hear the difference in gain between them (at the same RP RK ratio) as some might confuse gain with distortion, but you can feel it in the amount of compression..Impedance of the plate resistor in combination with plate resistance also factors into the tone..Generally high plates can have more low end..
IMO you might need to open the OD trimmer slightly to compensate for distortion levels going from low plate to high plate..But only slightly (around 5-10k on the pot)..If it's a drastic shift, like having to up the trimmer value then something else could be wrong..If you go to the higher value OD trimmer expect more gain distortion but also expect more low end response due to the shifting of the -3dB knee!!..So you may have tweak the bypass values on the OD

Tony

[jcsifu]

As some of you that helped me trouble shoot a switching issue are aware, I just switched my high plate clone resistors to low plates. I swapped out the V1A + B bypass caps to 10uf as well, but left the trim pot and resistor the same as they were (220k and 100k pot). I had too much compression and distortion when it was a high plate and wanted to be able to have better dynamic control of the break up. Now after the swap I am finding that I have to turn the trim pot all the way up to get the rich harmonic tone I like from a D-style amp. Is this normal?

I am thinking that if I switched to the higher value trim pot it would make a hotter signal and maybe that is what I need. I would parallel a 1.2m resistor on a 500k pot for the 350k value.

Or...

What if I switch the od values back to high plate but leave the low plates on V1. Has anyone ever done this?

Real low plates have the OD trimmer set differently, what you are experiencing is relatively normal.

I do have one quad 6v6 Amp setup with 150/120 into 100/100k. You could even try 150/120 into 150/120.



TM

I'm thinking I might try the high plate for OD stages. What was the main diff you heard in the 150/120 you built?