D'lite to Bluesmaster migration testing

[deiseldave]

The confusing thing is some manufacturers wired the the V1b side to pins 1,2,3.


While others seem to have the first triode on 6,7,8.

Are you saying that all 12AX7's are not wired the same internally?

[Smokebreak]

The confusing thing is some manufacturers wired the the V1b side to pins 1,2,3.

Hmm...wouldn't that be V1a then??

[JazzGuitarGimp]

I think the difference lies in how different amp manufacturers (as well as folks who reverse-engineer the schematic out of an amp) label their schematics. It seems some manufacturers claim pins 1,2 and 3 belong to the first (A) section, and pins 7, 8 and 9 belong to the second (B) section, while other manufacturers label their schematics with pins 7, 8 and 9 as the first (A) section, and pins 1, 2 and 3 as the second (B) section.

[deiseldave]

I think the difference lies in how different amp manufacturers (as well as folks who reverse-engineer the schematic out of an amp) label their schematics. It seems some manufacturers claim pins 1,2 and 3 belong to the first (A) section, and pins 7, 8 and 9 belong to the second (B) section, while other manufacturers label their schematics with pins 7, 8 and 9 as the first (A) section, and pins 1, 2 and 3 as the second (B) section.

I have been looking through different 12AX7/ECC83 datasheets, and have yet to see one that says 1, 2, 3 is the quiet side. They either say 6, 7, 8, or don't mention it at all.
In the AX84 thread, Merlin said "For valves with the same pinout as the 12AX7, the second triode is always the quieter. The reason being that the second triode brings the cathode pin out beside the heater pin (the cathode is low impedance and also next to the heater in any case, so hum is minimised.) The first triode brings the anode pin out beside the heater, so hum leakage is at a maximum".
I've been looking at the pinouts of various 12AX7's, and I don't see what he means. It looks like the anode on pin 6 is closer to the heater on pin 5, than anode on pin 1 is to pin 9. Very confusing. I wish I understood.

[Structo]

Check out this old GE data sheet.

Pin 1,2,3 is in the second position.

[deiseldave]

Check out this old GE data sheet.

Pin 1,2,3 is in the second position.

Confusing...

[martin manning]

Also notice there is no remark about one side having lower filament hum than the other.

[JazzGuitarGimp]

I've heard about the lower noise 6,7,8 side a few times. But I've always assumed (and obviously incorrectly) lower noise means less hiss, not less hum. This thread is the first time I've heard about the hum issue.

[deiseldave]

I just bit the bullet, and rotated the 12AX7's 180 degrees on the D'lite to Bluesmaster conversion. A little bit of PIA, but nowhere near as frustrating as finding out I forgot to order 121K or 120K resistors. Didn't even have the right values to parallel in.
I just stuck a 110K on the plate of the triode formerly known as V1-B (lol), and also between the 470K and OD trim pin 1. Should be close enough to move forward, right? Ordered correct value, and will replace when they comes in.

[Smokebreak]

Close enough for now, yes.
470K?
Are you changing the OD 1 and 2 (V2a/b) as well, and adding the extra tonestack at the end? Full conversion?

[deiseldave]

Close enough for now, yes.
470K?
Are you changing the OD 1 and 2 (V2a/b) as well, and adding the extra tonestack at the end? Full conversion?

Hi Smokebreak - I wasn't planning on second tone stack. I have been trying to work though the schematic that you provided, and determine what component changes would not apply to my conversion. The scheme you referenced me to shows R13 as 470K with a 47p bypass connecting to R14 120K then to OD Trimmer. Was I not supposed to change those? I previously had a 10M going to ground, followed by .05uf and 220K going to pin 1 of OD trim. Should I have kept that instead?
Also, do you think I would be better off to use 150K instead of 110K as a temporary sub on the V1b plate?

[Smokebreak]

Close enough for now, yes.
470K?
Are you changing the OD 1 and 2 (V2a/b) as well, and adding the extra tonestack at the end? Full conversion?

Hi Smokebreak - I wasn't planning on second tone stack. I have been trying to work though the schematic that you provided, and determine what component changes would not apply to my conversion. The scheme you referenced me to shows R13 as 470K with a 47p bypass connecting to R14 120K then to OD Trimmer. Was I not supposed to change those? I previously had a 10M going to ground, followed by .05uf and 220K going to pin 1 of OD trim. Should I have kept that instead?
Also, do you think I would be better off to use 150K instead of 110K as a temporary sub on the V1b plate?

Ok, that's what I was getting at...
Look at it this way. This amp, as a whole, is an entire system. If you study the other amps, you'll see similar topology, but different systems. If you break them down a bit, you have the clean section, and the OD section. They all have these 2 sections, but there are different sub-systems here, and different values.
Now, to stick a BM clean section on a D'lite OD section very well may be OK, maybe even great! But technically, the OD entrance on the BM is tailored and designed to work with the rest of the OD section, most importantly, with that post OD tonestack.
Compounding the potential problem is that the BM is an HRM amp(extra tonestack), and a lot of folks feel that the OD sound best when the clean tonestack is disabled. That's a whole other ballgame, but the point is that it gets tricky, and may be sonically unsatisfying when you start swipswapping within different OD systems of different amps. I consider the OD entrance as part of the OD network, even though it comes off the plate of the 2nd clean stage.
Check out the differences between the BM OD entrance, and the one for the D'lite. It's not the end of the world if you put in a 470K there, but chances are it will be muddy/congested a bit. Check it out and see!
But I would just change the clean section for now, and see where that gets you, then you can go from there. It's best not to make too many changes at once or you can't be sure what did what.
I would stick with 110K plate instead of 150K. Just find a 110K that reads high 150K may be too much, but again, check it out and see. Or go to 150K and bump up the cathode resistor a bit to 2K2 or thereabout.
Did you already do the PI?

[deiseldave]

Ok, that's what I was getting at...
Look at it this way. This amp, as a whole, is an entire system. If you study the other amps, you'll see similar topology, but different systems. If you break them down a bit, you have the clean section, and the OD section. They all have these 2 sections, but there are different sub-systems here, and different values.
Now, to stick a BM clean section on a D'lite OD section very well may be OK, maybe even great! But technically, the OD entrance on the BM is tailored and designed to work with the rest of the OD section, most importantly, with that post OD tonestack.
Compounding the potential problem is that the BM is an HRM amp(extra tonestack), and a lot of folks feel that the OD sound best when the clean tonestack is disabled. That's a whole other ballgame, but the point is that it gets tricky, and may be sonically unsatisfying when you start swipswapping within different OD systems of different amps. I consider the OD entrance as part of the OD network, even though it comes off the plate of the 2nd clean stage.
Check out the differences between the BM OD entrance, and the one for the D'lite. It's not the end of the world if you put in a 470K there, but chances are it will be muddy/congested a bit. Check it out and see!
But I would just change the clean section for now, and see where that gets you, then you can go from there. It's best not to make too many changes at once or you can't be sure what did what.
I would stick with 110K plate instead of 150K. Just find a 110K that reads high 150K may be too much, but again, check it out and see. Or go to 150K and bump up the cathode resistor a bit to 2K2 or thereabout.
Did you already do the PI?

That helps a lot, Smokebreak. Thanks. I haven't done the PI, yet. I was planning on doing that next. I think I will change the OD entrance back to where the D'lite was, for now.
Two questions: I looked again at paralleling resistors that I have to get closer to 121K for the V1B plate. I can parallel 470K with 150K and get 113.7K, or 470K with 180K for 130.1K. Should I use either of these over the 110K that I currently have in there? Or, am I majoring on the minors, here?
Question 2: The mid pot for BM shows 15KB. Dlite has 250KA in there. I know I have a 25KB. Will that be adequate?
Thanks for the help.

[Smokebreak]

I think you're obsessing over that 110K a lil much
While it does matter, the 110K while be able to give you a very good sense of things, for now. It's not like you have to decide now, like forever. Just clip stuff in, or do what I usually do...just fly components all over the place, soldering to whatever you can grab, till you find your recipe, then make it permanent. It shouldn't take too much time to test 110K vs 130K.

25KB for the mid is good. they're wired as a variable resistor anyways, so the same settings can be achieved on any pot greater than 15K. The 250K would just allow waaay more mids, virtually lifting the tone stack, in the BM/Marshall config.
Also, look at the BM vs the Dlite stack. The mid pot is seperated from the other two controls in the Dlite. Apples and oranges, kinda.

[deiseldave]

I think you're obsessing over that 110K a lil much
While it does matter, the 110K while be able to give you a very good sense of things, for now. It's not like you have to decide now, like forever. Just clip stuff in, or do what I usually do...just fly components all over the place, soldering to whatever you can grab, till you find your recipe, then make it permanent. It shouldn't take too much time to test 110K vs 130K.

25KB for the mid is good. they're wired as a variable resistor anyways, so the same settings can be achieved on any pot greater than 15K. The 250K would just allow waaay more mids, virtually lifting the tone stack, in the BM/Marshall config.
Also, look at the BM vs the Dlite stack. The mid pot is seperated from the other two controls in the Dlite. Apples and oranges, kinda.

Wow. Thanks Smokebreak. I'm learning some cool stuff here. Almost done with changes. Too late now. But, next time I will be more liberal with temping stuff in. That would save a lot of time while I'm navigating towards the sounds I want. Great stuff. Thanks again.