Dumble ODS #123?

[Structo]

I can't remember where I found this schematic but I was organising some files on my PC and saw this, never really looked at it much.
The print is titled #123 but that's all I know about it.

It shows a tone control just before the Ratio Control pot. I thought that a bit off the reservation.
Although it may be a nice feature.
Sort of a poor man's HRM.

Anybody know anymore about this amp? Is it an official Dumble?
It has high plates, and a 100K resistor on the pre-out jack before the PI.

I don't seem to have a power section or supply schematic in my files.

[UltraHookedOnPhonix]

It shows a tone control just before the Ratio Control pot. I thought that a bit off the reservation.

That's the, "high frequency taper" control. Appears in other ODS amps including #94.

Here's a pic of 123:

[ChrisM]

OD Tone seems just a simple a high cut that a lot of us use in similar fashions to smooth out our OD channels.

Wonder where the schem came from...

[UltraHookedOnPhonix]

Wonder where the schem came from...

Forum member ElectronAvalanche originally posted this information:

Since there is so much talk about #124, here is how #123 looked like. I saw the schemo only, but supposedly that amp was a great sounding one as well.

ODS 100W #123.

First stage:
220k, 3k3, 5uF
Tone control: as in the schemos available (330pF, 0.1, 0.047)

Deep switch wired, 250K bass pot and a 100K middle pot.

second stage:
150k, 2k2, 5 uF, local feedback: anode -> 22M -> 0.047 -> 22M -> grid
220k grid stopper, no cap across it !!!!
0.047 decoupling

OD section:

220k series, 500k (!) trimmer -> 68k -> grid
220k, 3k3, 5 uF, 250 pf anode -> cathode
0.01 uF -> 100k -> 100k pot -> 150k ->grid
150k, 2k2, 5uF, 250pF anode -> cathode
0.0047 uF decoupling
150k -> 1M (master) -> Pi
from the ccw of the 1M to 500k pot to 0.022 uF to ground (tone control of OD!)

PI: as in the schemos, 820, 24k, 1M, 0.1 uF, 0.01 uF (I am not sure about this one tho). Tubes were 7581. 420 V on the anodes.

The preamp had quite low voltages:

V1a: 190 V, V1b: 192V, V2a: 300 V, V2b: 320V

[ChrisM]

Typo on voltages? 300V on V2 cant be right.

[talbany]

220k series, 500k (!) trimmer -> 68k -> grid

Interesting another one w/ 220k 500k OD entrance...It's probably scratched down as well...Still. 2 good sounding ODS's with big trimmers....Thanks Tom

I think that amp belongs to a guy at Music Exchange over here near Baltimore... he had 2 and was asking 50k for em..


Tony

[JD0x0]

Typo on voltages? 300V on V2 cant be right.

maybe he means 300V on V3, V2 is usually around 198 while V3 is closer to 300. At least from what ive seen

[Max]

Great amp. Has been built for the same musician as the one offered by Bruce Sandler (Guitar Exchange, Baltimore). Both are "sister" amps and looking very similar with similar cabinets. But as far as I now remember (look by yourself at Bruce Sandler's "gearpage" site) both had different OT's. (#123 switchable between 4 and 8 Ohms and the sister amp just 4 Ohms, but may remember wrong).

#123 has a "flute" kind of OD tone, very rich natural distortion overtones that do not separate themselves from the tone. Stays "clean" in clean mode with a strat up to nearly full volume. Has been made for a 1956 maple neck strat.

It has not been de- and regooped for the schem. I saw it before and after the schem had been drawn. How the one who drew it, did it, I don't know. But whatever he did, it altered the sound of #123 in some way. Me and other musicians liked it a bit better before the schem had been drawn then after it. No idea why. But indeed: a great amp. Very versatile. I liked it (as most Dumble ODS) best with the taper turned full "on", that is without attenuation of the OD highs spectrum.

Cabinet has 2 x EV12S like it's sister amp in Baltimore.

Cheers

Max

[Structo]

All I seem to have is the preamp, is the power amp and supply also available?

Can't think of a reason for the amp to sound different after the schematic was drawn.
Perhaps some of the fairy dust was disturbed.

[martin manning]

...Can't think of a reason for the amp to sound different after the schematic was drawn.
Perhaps some of the fairy dust was disturbed.

Perhaps the scribe was poking around tracing leads and displaced one from its original position?

MPM