Here's a write up from erwin I believe on another post on different OTS models that discusses the different tonestacks as well


Non Hrm classiq EQ is the oldest style of dumble amp. A bit more rooted in the
raw fenderish tone. This is the amp that made his reputation. This
would be like early Lindley, Browne, Lowell George, the first
incarnation of his amps.
It can sustain like a mofo! It is a singing OD for sure.
Not much compression, very touch sensitive and dynamic....

Second the Non-HRM Skyliner EQ  low plate is a variation of the above. Dumble modded
several of his older amps with a new tone stack he was developing,
know as the skyline eq because it's output viewed on a scope resembled
a city skyline.
It is a little less Fender but still a somewhat lower gain affair. It
has the same gain as the vintage amp but the new EQ is more "signature dumble" and a little less Fender. Improved cleans from th Vintage model.
It still sustains like a mofo, has a bit better string to string definition and is a little more refined in the tone shaping.

Non-HRM Skyliner EQ  high plate is where he went next, same as above but now the
gain staging is not classic fender. It has more headroom, definition, and punch, more lively and responsive cleans, smoother OD, and a small bit of compression, very touch sensitive, lots of sweet singing tones.

HRM Skyliner EQ   HRM stands for
"Hot Rubber Monkey". This is a second tone stack just for the OD
channel. It is more or less a Marshall style tone stack this allows tone
shaping of the OD independent of the cleans.
A real Dumble of this ilk would be called a Skyline HRM. Smooth as silk, goes from clean to mean like no ones biz. Transition
between is amazing. You can pick clean, a bit dirty, grinding, soaring, all
with your hand and all smoothly with definition. No rasp or buzz. Very refined. Gorgeous smooth tones. A little more compression that the above amps but not in a bad way. Very natural. The dynamic response is second to none. This amps feels like it breathes with you after awhile.
Smooth singing overdrive, completely dynamic, never any rasp or buzz, no IM distortion or other uglies.

Blues Master. Think raw early Fender/Marshall
tone on steroids. The tone stack is decidedly bassman territory,
however because of Dumbles many other difference it is far better IMO.
The cleans here are the best cleans I think I have ever heard, dumble
or otherwise. The cleans will sing and sustain!!! The OD is much less smooth and much less compressed than the above amps. It has some early Marshall vibe to it. Boosted cleans with this amp are to die for. The OD is a bit more raw and edgy then some of the other offerings but with boosted cleans you get the smooth side of things and with the OD you have a less polite and refined tone.
Somewhat like the first Dumbles, though different. Lots of punch, sustain and singing but not as smooth as some of the other offerings. This one can be thick and dense too. Not dark and crappy, just "meaty"...
Open clean cleans to mean and a little rude.
Big fat sick blues machine. Lots of character or soul. This amp will try and steal your girl.Like a tuxedo on a cowboy?.... It can play nice but it can still stomp in the dirt.
last is the same as above with the HRM OD tone stack which gives a little more tone shaping and refining in the OD section.





hope this helps!

Gregg