I may have to try the CV4024 in the PI spot again for shits and giggles. I'll have to drop the chassis again to adjust the PI trimmer though... sigh


Gregg

I normally keep the bright pulled on mine, but i have warmer speakers, too. Also, in regards to the OD, whebn i use itm i normally keep my HRM bypassed, so that my OD tone matches my clean tone pretty well, again pretty much building on the clean tone. Also, I have found that when using the c-lator i like it better with the output turned up to about 1 o clock, and the masters adjusted to the appropriate level for the venue. Pushes the PI nicely and brings out the punchiness and spank of the amp

Gregg

+1 on this. I switch to the TAD 6L6WGC-STR when i want a less stiffness than lower mids than the Tung Sols provide.

These Bm's are fun to tweak, aren't they? I still find new sounds that blow me away every couple of days or so 

Also, in my testing i found there was a pretty large voltage difference between having a 12AX7 vs a 12AT7

V3   12AX7 GE Long    Pin1: 239      Pin 3: 39.2         Pin 6: 232     Pin 8: 39.4



V3   Mullard CV4024  (12AT7)   Pin1: 185.1   Pin3: 55.2       Pin 6: 180.2  Pin 8: 55.1

The 12AT7 sounded pretty good with about a 8 volt swing between Pin 1 and Pin 2, and with the JAN Phillips 6L6WGB's in the output spot, pushed hard and biased hot. With standard biasing, 6 volt swing, and standard 6L6's, not so much.

Gregg

Here are some notes from guitarampliferblueprinting.com:

Some basic tube facts
• 12AX7
o Has a published spec gain of 100
o Has a publishes spec current output of 1.2 milliamps
• 12AT7
o Has a published spec gain of 60-70
o Has a published spec current output of 10.0 milliamps (ten times that of the 12AX7 as a side note)
As a third example, a 5751 has a gain which is almost identical to the 12AT7 but it’s standing current is 1.0 milliamps (about the same as the 12AX7). But, there is a third factor, transconductance, to be considered. The 5751 has a transconductance of about 1200. A 12AX7 has a “TC” of about 1600 and a 12AT7 has a TC over 5000. These three tubes act quite differently. A 5751 and 12AX7 are much more closely related than the 5751 and 12AT7.
We will stick to the basic 12AX7 and 12AT7.


When you push your amp hard it is not as much the output tubes distorting as it is the phase inverter breaking down and distorting. We are talking output stage distortion here. We are not talking about how you may have messed up the signal with preamp tube distortion and compression already. The phase inverter may be the hardest worked tube in most amps. I cannot begin to count the times when I have found phase inverters that were long past their service life. When you change your output tubes change that phase inverter. At the least change it every other output tube change.

Many folks think that when they want to have their amp have more clean headroom they can insert a 12AT7 in place of the 12AX7. Very true. (By the way, the 12AT7 in a first gain stage is an awful tone generator in a guitar amp. If you want to drop front end gain use a 5751 (gain of 60-70) or a 12AY7 (gain of 40). The 12AY7 was the first gain stage in the classic Fender Tweed Bassman, Deluxe, etc.
Going from a 12AX7 to a 12AT7 in the PI (phase inverter) will yield a change in output tube distortion, touch, and output dynamics in most amps. Is this because the gain is lower in the 12AT7? 10% yes perhaps. The lower gain is a factor but the larger factors are:
• We have almost 10 times the current available to drive the output tubes before the phase inverter starts to break down.
• We have a transconductance of 5500 vs 1600 of the 12AX7. Keeping this simple, it means it takes a lot less input signal for a given output signal

So, I'm thinking of installing VVR on the power section of my BM, using Hall Electronics VVR2 and i wanted to pick the brains of the more knowledgeable techs on here. In the diagram it shows using diodes to keep the power and pre amp power nodes seperated. Their diagram shows two, one which would go on the OT Center Tap, and one that would go to the rest of the amp. On the OTS, would I need 3 diodes, one for the OT Center Tap, One for the PS-2 Node going into the PI, and one for the PS-3 Node going into the "L" line which feeds the preamp?

Thanks,

Gregg

12AY7's or 5751's are a good choice

Gregg

It may be putting out more than an original, just due to the internals being new, the main caps, and such.

I like the OD on my BM for some things, but even after a couple of years of tweaking and tube rolling, i still just prefer to run my tri-boost into the clean channel and just drive it that way. I also have a clean boost on the other end, as the last pedal in my loop going thru the c-lator,  so i can push the PI and power section as well. Outside of that, i'm an admitted fuzz addict and use fuzz quite a bit as well

Gregg

The Marshall tones on the BM are more early type Marshall, so like a JTM 45, maybe Plexi-ish. Since the early Marshalls, like the JTM were based on Tweed Fender circuits, then the BM overdrive is more like a cranked tweed or early Marshall. The HRM stack, especially with the PAB engaged to bypass the first stack makes it sound slightly more Marshallish, especially if you tweak the HRM stack that way. Also, it is thought that the HRM and BM's OD were designed to be used with the PAB enaged, bypassing the main stack. If not you are going through two tone stacks instead of one which can sound like mud...

Gregg

well, the more presence you add, the stiffer the response can be as well.

I second that. It's a whole other animal

just a heads up you may not like the 12AT7 in the PI spot. Significant loss of volume and tone (i speak from experience)

where do you have your presence set?