Okay, so I started thinking about what could be making my Bluesmaster so Bass heavy and lacking the brightness i thought it should have. It was kinda frustrating, as the clean channel was almost where i wanted it, but lacked that Fendery shimmer that i craved, and the OD channel was just muddy fizz. Not what i expected. Sure i only had 40 or so hours in it, but still the basic tone should be there. I was ready to perform surgery, changing slope resistors, bass pots, adding treble bleed caps and all sorts of mods, but i got to thinking there has to be a better way, so i started playing around with one of the basic components that the D style amp seems fussy about. The tubes.

First i started with the pre-amp tubes. I had originally installed 7025 tubes from the tubestore.com based on the recommendation of a buddy of mine in all 3 spots. these are supposed to be high gain low noise 12ax7 tubes. they are low noise and high gain, but flat as a pancake tonally (at least in the BM), and they are made by God knows who, so i changed V1 & V3 to some Sovtek 12AX7WA tubes that i have had for about 8 years now and have seen service in my Sovtek Mig50, and my Ampeg J12 and have always sounded very good indeed. I also changed V2 to a JJ 12AX7 i had purchased just for the BM and voila, things instantly got better!! no more flat, boomy, over bassy dull sound on the clean channel. Hot Damn! However, the OD channel was still fizzy. Bummer.
Originally, i had chalked it up to the NOS JAN Phillips 6L6WGB being just not right for the amp. The voltage was just too high, and I couldn't bias them any lower that about 47ma or so, plus they would creep up to 50ma. they sounded like a nice overdriven blackface when pushed, but again the OD channel sounded poopy. I was about to take them out when i remembered my amp had a feature that others didn't... the Sag switch!. The nice thing about the Sag switch is that in my amp it drops the voltage across the tubes down to 425 volts, which allowed me a wider range of bias control from 35ma-45ma, just like it should be able to! So i set the bias to around 44ma, and they stayed there! Now the amp sounds even more blackface fendery on the Clean channel eith every guitar i put thru it, whether it be my old sheraton, my dano, or my strat, and the OD channel sings like no tomorrow! The bass is no longer loose or flabby with or without the deep switch on and i can actually utilize the bass knob! what a concept!!

I've never been so happy in all my life!!!  , and all it took was he flip of a switch yeehaw!

I'm happy for you...   

... let us know how the lp tubes will work out for you.

Hello plasticvonaband,
This is first time for me to write here. I am not a native English speaker, so, sorry for my poor English. I don't know much about amps' technologies, either.
I also purchased HRM Blues master 50W model in last November, and I have been having the same problems you had and dissatisfaction about this amp. Too much bass and dull treble, flat and not sexy tones (not like Fender amps), and harsh overdrive sound (it's not creamy at all as I expected for the D-style amps).

I read your topic and knew that you made your amp's normal sounds better changing the preamp-tubes to SOVTEK 12AX7WA. Were you able to get a better overdrive sound by that arragement, too?
One thing I didn't understand was that what the SAG switch was. I asked them to install 1/2 power switch and PI Trimmer, and it has OD trimmer, too. But it seems like SAG switch is the different thing. Is that a special one you only have or all HRM bluesmaster has somewhere inside?

Anyway, I am going to start changing the preamp-tubes. I hope that it will work well to me, too

@ Hiderek: Your english is fine, bro! it is actually better than some for whom it is the first language! As far as the Sag switch, it is a basically a heavy duty switch with a large ceramic resistor mounted to it that sits across the center tap of the HT Leads to simulate having a tube rectifier instead of a solid state one. tube rectifiers tend to "Sag" and drop voltage a little when pushed which makes the amp sound "spongy" (think of an older tube amp and how they respond when pushed) Nik came up with the solution when i asked if i could have both a tube and solid state rectifier in my BM, but the power transfromer does not have a 5 volt tap.

As far as the Sovtek tubes go, I have to agree with bluesfenderman, i think my initial response was a bit of a honeymoon/crush phase, because now, even though i have the proper brightness, the are a bit harsh and not very warm. I have a pair of ANOS GE Long plate 12AX7's for V1 and V2 coming from KCA NOS Tubes, along with a CV4024 for the phase inverter spot, which come highly recommended for D style amps. I also have a pair TAD 6L6WGC tubes coming to swap out mt lil 25 watt NOS JAN Phillips 6L6WGB's which, while sweet sounding are not going to last long in the BM, even with the reduced plate voltage.I also will be picking up some TAD 6L6GC-STR long bottles and winged SED'S just to try em out.

I still plan on swapping out the bass pot, slope resistor,  possibly putting 3 different values on a 3 way switch, and adding some additional bright caps on all three volume controls on 3 way switches, just to have a little variety, and maybe adding a Local Negative Feedback Loop. Also my c-lator was ordered yesterday, which should help smooth things out and add some brightness.

The OD tone will smooth out over time as the amp burns in. Try playing an mp3 player with the volume turned down a bit with some smooth jazz in to the amp to help burn it in. also, remember that the gain from the clean channel affects that OD channel so if you dial the clean channel gain up and down, it can smooth out the OD or harsh it up, and the OD trimmer on the rear makes a big difference on the character of the OD.

Also, i am starting to look at the HRM OD tonestack a little differently. I don't want to rehash it here, but the thread i started on my thoughts on the OD tonestack are here--------> http://ceriatoneforum.com/index.php?topic=3048.0

@bluesfendermanblues: I will have to try the JJ'ss in V1 & V2 and the Sovtek LPS as well! thanks for the input and advice, it is always welcome!!

These Dumble style amps are something else aren't they? Mine is approx. 6 months old and it surprises me every time... sometimes I hate it, sometimes I love it. Every now and then I fiddle round with the tone controls and end up with a different sound. I have been playing it more often and I now have the impression that the speakers (Celestion G12-65 Heritage) are (slowly) starting to burn in, in any way the amplifier seems to be sounding warmer and warmer though it's definitely not yet what I've heard on some clips on the internet.

Hmmm I think I don't agree with this statement.
I own an OTS and BM HRM and I prefer BM over OTS. It can be a bass heavy amp but that can be fixed... btw just as much as I'm trying to improve (read mod) the BM... I'm doing the same for OTS. ...and at the end of the day I still prefer BM

Same here, no problems with the BM sounds, with no valve changes.
I have a BM and plain OTS, both stock. The BM is much better I think. It's true the BM is dark, but it only needs a Celestion Gold, and the treble and presence set high, especially if you run the Master volume high. I'd say that stock, with the original JJ valves, my BM is one of my top 3-4 favourite amps, and probably the one I play most. A very special amp.
All I want to change is to lower the PAB and reverse the deep switch.

I agree with all of you, my BM is the best amp i have ever played through, i don't want anyone to misunderstand and think i'm dissatisfied with it, i love it! i really enjoy how interactive all the tone controls are and how the OD can go from mild to wild. it is second only to my much loved and much missed blackface princeton reverb, but let's face it, by the time i got it was almost 30 years old and modded 99% of the time my BM amp is perfect, it is by far the warmest fullest sounding amp i have owned, and i have owned a ton of amps over the years, and every day it just gets better; there's just that 1% of the time that i wish it was a lil brighter, a lil less bassy, and the post od tonestack could be either easily adjusted or bypassed, that's all.