plate/cathd R values -choices Q

[Pete]

Recent builds I've seen (like pics and schems of the dumbleLite) show the use of the HRM values (220K/3.3K, 150K/2.2K, 180K/2.7k, 120K/1.8K).
Is it universally accepted that these are superior sounding overall to the early 80s era (#124 et al) values of 100K/1.5K, and to be used in an amp with or without the post OD stack?

Has anyone done much comparison? Not easy to do via quick A/B switching. Was wondering if there is a consensus on the differences in sound (or feel etc.)? Or is it simply that the higher plate R gives easier breakup? Does that mean if you are going for ultimate clean you would use the 100/1.5?
enough questions for now??:-)?

[oldmacman]

Play around with it, and keep in mind that the resistors don't always have to be in the 67:1 ratio. Try greater than 67:1 for the first stage and less than 67:1 for the second stage. Dumble did this in several amps. See the Blues Master schematics that were posted here a while ago for some ideas, but keep in mind that those values are specific to that particular amp, and you'll need to experiment. Also remember that changing the cathode resistor without changing the cathode bypass capacitor will change the frequency response of the stage (see http://www.aikenamps.com/CommonCathode.htm for the math)

Ben

[Normster]

I tried different preamp preamp values in every Dumble I've built so far. Each seems to have its own unique sound, but always with a Dumble flavor. For a rock/blues amp I think it's hard to beat #124 with the traditional 100k/1k5 pair. The 97 HRM probably has the best fusion/Robben Ford tone and the Hybrid-A gets me pretty close to Carlton. It's pretty easy to see why Gary and Scott worked so hard to give the Glaswerks all of the different voicing options.

[Pete]

thanks, great link, I guess it's time to get out the soldering iron and try out a few things. There are a lot of variables in this area, and it seems easy for me to get lost.

Play around with it, and keep in mind that the resistors don't always have to be in the 67:1 ratio. Try greater than 67:1 for the first stage and less than 67:1 for the second stage. Dumble did this in several amps. See the Blues Master schematics that were posted here a while ago for some ideas, but keep in mind that those values are specific to that particular amp, and you'll need to experiment. Also remember that changing the cathode resistor without changing the cathode bypass capacitor will change the frequency response of the stage (see http://www.aikenamps.com/CommonCathode.htm for the math)

Ben

[Pete]

thanks, that's a nice evaluation of the different types. I'm going for max headroom/clean from the 1st stages so I guess I'll leave the 124 style values in there for now. I'm assuming that is the best way to go for that result. I've never read anything about the differences in lower to higher values and how they effect things.
I'll play around with the OD stages. I'm trying to get a smooth transition and a good sound in the low range of OD (It's a non hrm 100w). Then there is always more available with the PAB.

I tried different preamp preamp values in every Dumble I've built so far. Each seems to have its own unique sound, but always with a Dumble flavor. For a rock/blues amp I think it's hard to beat #124 with the traditional 100k/1k5 pair. The 97 HRM probably has the best fusion/Robben Ford tone and the Hybrid-A gets me pretty close to Carlton. It's pretty easy to see why Gary and Scott worked so hard to give the Glaswerks all of the different voicing options.

[Icetech]

I am a bit confused on something.... you guys talk in the plate/cathode values...

BUT say my b+ is 20v higher than yours... or whatever you consider standard (cause my shit is never right on), wouldn't it be better to use the plate voltage/cathode ratio instead of resistor/cathode...

I could be way off though:)

[Bob-I]

I am a bit confused on something.... you guys talk in the plate/cathode values...

BUT say my b+ is 20v higher than yours... or whatever you consider standard (cause my shit is never right on), wouldn't it be better to use the plate voltage/cathode ratio instead of resistor/cathode...

I could be way off though:)

If your B+ is that high, you should use a dropping resistor in the power supply rail to get it in line. These Dumble like ckts like the plate at about 200V so the B+ needs to be adjusted to achieve this.

[Darkbluemurder]

thanks, that's a nice evaluation of the different types. I'm going for max headroom/clean from the 1st stages so I guess I'll leave the 124 style values in there for now. I'm assuming that is the best way to go for that result. I've never read anything about the differences in lower to higher values and how they effect things.
I'll play around with the OD stages. I'm trying to get a smooth transition and a good sound in the low range of OD (It's a non hrm 100w). Then there is always more available with the PAB.

I tried different preamp preamp values in every Dumble I've built so far. Each seems to have its own unique sound, but always with a Dumble flavor. For a rock/blues amp I think it's hard to beat #124 with the traditional 100k/1k5 pair. The 97 HRM probably has the best fusion/Robben Ford tone and the Hybrid-A gets me pretty close to Carlton. It's pretty easy to see why Gary and Scott worked so hard to give the Glaswerks all of the different voicing options.

When I changed the plate/cathode values in my Bandmaster and my Deluxe from 100k/1k5 to 220k/3k3 headroom appeared to increase.

[Icetech]

bob-i yeah, i went through and fixed my voltages a little recently when looking for that oscilation prob.. somehow my driver plates were only running like 240... i bumped em to 309v (i think) and it made a giant difference...

And after i posted that last post i kinda figured that maybe i should just make sure my voltages are right and no worry bout the wording:)

[Pete]

When I changed the plate/cathode values in my Bandmaster and my Deluxe from 100k/1k5 to 220k/3k3 headroom appeared to increase.

thanks, I appreciate the comment. I'm not that knowledgeable about this subject and i was wondering what to expect when experimenting. I was under the impression that higher plate R gives less headroom. guess I'll have to put some in and see for myself.