Just for fun: Attempt at #40 schematic...

[ic-racer]

I'll put it up here for discussion before putting it in the files section. I can only make out a few values from the #40 pictures. Most of these values are from the '70's Schematic' and some are guesses. At least I think the overall wiring follows the #40 pictures.

[Bob-I]

Looks good. I'll bet it'll get that David Lindley/Jackson Browne era tone. That was the one that send me on the tone quest back in the last 70's. I got pretty close with my modded Twin but this schem will nail if for sure.

[odourboy]

Nice!

[Structo]

Good work!
Sometimes I think when we are after a grail type tone we lose sight of the fact that a new amp with new components probably won't sound like the amp we are cloning, given the fact that an amp that is 30+ years old has drifted in values and has a certain browner tone compared to a brand new amp.
YMMV

[Bob-I]

Good work!
Sometimes I think when we are after a grail type tone we lose sight of the fact that a new amp with new components probably won't sound like the amp we are cloning, given the fact that an amp that is 30+ years old has drifted in values and has a certain browner tone compared to a brand new amp.
YMMV

Good point. I like to approach this building like the big man would've. Don't go for historical accuracy, go for tone.

[ic-racer]

The problem with a thread like this is that it likely will turn into a 'build' thread...

I do have a set of 50w iron just waiting for something.

Natchanis (a member here) has a nice chassis, just made for the #40 schematic ( http://vasinguitaramp.tripod.com/id2.html )

So, I was thinking of the pros and cons of a #40 build, compared to doing a HRM Bluesmaster.

PRO #40 build:
Chassis easily available (HRM/FUNK chassis in short supply)
No PCBs, unlike the HRM.
Simpler circuit (only one relay, no voltage regulator, 50w, less knobs etc.)
Not as much secrecy surrounding the pictures or schematic.
I think it would look way cool in a suede covered cabinet!
I started playing guitar in the 70's so there would be cool nostalgia to this build (I used to listen to 'Running on Empty' on the radio driving my first car...)
Best reason to do #40: I think I would more likely be SURPRISED at how good it sounds vs the HRM/BLUESMASTER. I suspect with a hyped, complex, multivariable build like the HRM, one would more likely be DISAPPOINTED at how it initially sounds!
With this 'antiquated' circuit of #40, the impression is that it is 'not as good' as the later 90's amps. I bet it has a killer straight forward "Rock" sound for leads and chords. Something that does not draw attention to itself, but lets the music speak. A good 'general purpose' amp.

CON #40 build:
1) I really don't need ANY MORE AMPS!!
2) same as 1
3) same as 1
4) same as 1

[Bob-I]

Those chassis look very nice. I like the ODS Reverb myself although I'd use the single tube reverb leaving an extra tube. Maybe independant channels with concentric tone control pots

[nickt]

The only problem with the chassis is it says "Dumble".

It may not be a trademark but it's "wrong" (as in "a massage from grandma is just wrong"). If it says Dumble you're never going to be able to put it on ebay without someone getting annoyed.

If it didn't say "Dumble" I'd buy one of the ODS ones like a shot.

[markmalin]

The only problem with the chassis is it says "Dumble".

It may not be a trademark but it's "wrong" (as in "a massage from grandma is just wrong"). If it says Dumble you're never going to be able to put it on ebay without someone getting annoyed.

If it didn't say "Dumble" I'd buy one of the ODS ones like a shot.

Hm... you can't just go putting someone else's trademark on your own stuff, can you?

[ic-racer]

Well, there are US laws on all that stuff and anyone in the business of selling amps needs to know those. I don't sell amps and I'm no trademark lawyer, and don't know those laws, so, I won't comment and let you guys battle it out

Just to point out another way to look at it, though. Without discussing legal matters, I think it can be seen as ethically "wrong" to put one's own trademark on someone else's circuit.

[Structo]

I thought we went through this before and discovered that the name Dumble is not trademarked?
But, I still think it is unethical since you can be sure someone will try to pass one of these off as the real deal given the current market price for a Dumble amp.

[jaysg]

We've lived this discussion ad nauseum. Please drop it for the sake of talking about early Dumble amps, like SN 0040. Anyone can buy the Bangkok chassis and use steel wool or paint wherever they feel led. If enough people politely request it, I'm sure he'll create an alternate silkscreen.

[bcook]

Back to your schematic, you'll need a resistor paralleling the accent switch & cap. The PI needs a DC path to ground.
-Bob

[ic-racer]

We've lived this discussion ad nauseum. Please drop it for the sake of talking about early Dumble amps, like SN 0040. Anyone can buy the Bangkok chassis and use steel wool or paint wherever they feel led. If enough people politely request it, I'm sure he'll create an alternate silkscreen.

Thank you!

Now for more discussion about #40;

I really didn't realize this until I had put all the pieces of the 70's schematic together but this amp has only a single master. It has no OD trimmer either.

I actually think that is kind of cool. Like this is a real 'amp enthusiast' circuit, because you need to know how to use a soldering iron to set it up. But then once it is set up, it is customized to your playing and you don't have to worry about losing your favorite settings.

Some other interesting things are the use of 68k grid stoppers on V1 and V2.

There is also a 'mystery component.' Under the 'death cap' in the pictures there is a large resistor to ground. In my schematic I made this a 1 ohm 'biasing' resistor (none on the other tube??) but if anyone has any other ideas I am open to suggestions.

[ic-racer]

Back to your schematic, you'll need a resistor paralleling the accent switch & cap. The PI needs a DC path to ground.
-Bob

Yes, thank you.

I see the resistor but it does not look like 390r.

The NFB looks like 820r and I know Fender used 820r and 100r in a similar setup. The pictures actually do look like 100r so I'll add that in.

Schematic updated to version 1.1.