Just to summarize how different or similar my amp wound up being compared to the Overtone:

Different chassis (black adonized aluminum)
PT and OT are Hammond Fender Twin style
Four 6l6 tubes
50/100 switch and LED to indicate 50w mode.
Standby switch wired like a Dumble
Strict adherence to Dumble grounding scheme and lead dress
2 resistors to 'lift' the heater voltage from ground, like Dumble
Separate relay transformer
290uf caps (Dumble had 300uf)
350k OD input trimmer
4.7uf on V2 in place of 1.0 uf
Switchcraft jacks throughout, except FET jack, which is Kobicon.
Ground switch wired with a center off switch.
Main power LED powered with external diode and resistor
4 Bolt carrying handle put on the cabinet
Fender chrome corner protectors put on the cabinet.
Aluminum pieces on front of cabinet replaced to look like original
Once I get my hands on some black Fender grillcloth, this will go on the front plate.

With the exception of a few component changes listed above, and changing the color of some of the wires on the boards, the Ceriatone boards were pretty stock. (The Ceriatone Power Capacitor board was not used)

I used parts of a "Overtone" kit to make my #124 replica. My schematic is here:

http://ampgarage.com/forum/files/1z4_415.pdf

Here is a picture showing the ends of the shielded wire and the bus

I used that long straight piece for the buss bar.
I used the next thinner piece for the links from the pots to the buss bar.
I used the skinny ones that look like resistor leads for the shorts on the switches.

Here is a thread to 9 pages on the construction of my amp. You might have to join that forum to see the pictures. Joining that ampgarage forum is probably a good idea anyway, as there is a lot of good info in the old posts, and there are many people to help with new questions.

http://ampgarage.com/forum/viewtopic.php?t=4294

I have my amplifier wired such that if the power is cut to the OD relay it stays in "OD mode" rather than clean. I suspect Niki wired the Overtone in the same manner. Therefore, it seems as if your amp is behaving as if you have lost power to the OD relay. Try searching for a loose solder connection at the switches at the back of the amp. Also check the power lines to the relay. See the photos of my amp, which is probably close to the Overtone.

I tried out some different 12AX7s and found a phase inverter tube that could be perfectly DC balanced with the trimmer.

Here is the latest sound clip:

http://soundclick.com/share?songid=6455534

Actually it is NON-HRM. The HRM amps have three additional trimmers to play with.

Any particular reason for Neutrik over Switchcraft? Or just personal preference?

Let us know if you are doing any mods or changes to the circuit. Pictures would be great also!

The later '90's' Dumbles, though, use a DIN connector (like the Overtone), so Mr. D switched over for some reason...

Groove Tube used to make an amp with a rack space. In that design the empty rack was the first space and the amp (which also looked 'rack mounted') was just below, with the tubes hanging below the grill plate. I checked their site and don't see that model listed any more.

I have yet to try my rack mount delay (with adjustable in/out levels) to see if it has enough input/output adjustment range to match the impedance of the 'effects loop' without using a Dumbletor.  Have you tried yours?

The 80s Dumbles used Switchcraft 5-pin XLR connectors for the footswitch. I got my XLR jack and plug from mouser.com. My chassis came with pre-drilled holes, but they mount the jack up-side-down compared to a real Dumble. On the real thing, the little button is on the top, not the bottom.

Her is the info for the 6v transformer:

41FD010                       1        6.810            6.81
         Xicon Heavy Duty Pow
         TRANS FIL 6.3V 1A

From Mouser.com

Here is a quick guide to the Overtone.

********Front Panel:**********

FET: This input is for an acoustic guitar pickup.
NOR: This input is for an electric guitar

Volume: Sets the amount of gain for the preamp section. Use the "Master" to set overall amp volume. Higher levels of the Volume will distort the 'Overdrive' channel more.

Bright Switch: Adds a treble boost to both channels

Mid Boost:  (similar to the bright switch) Functions in both channels; adds some extra kick, especially in the overdrive channel.

Jazz/Rock: The Jazz setting is a quieter, lower gain setting.

Treble/Mid/Bass: These self-explanitory controls function in both channels. They are bypassed with the "PAB" (preamp-boost)

Drive/Ratio: These function only in the "overdrive" channel. The Drive, works in conjuction wth the "Volume" to control the overall gain or distortion. The Ratio is a seperate master volume. To set the Ratio control, go to the clean channel and set the overal clean loudness of the amp with the Master control. Then engage the "overdrive" channel and adjust the Ratio control to get an appropriate loudness of the overdrive channel.

Master: sets the overall loudness of  the amp. Raises and lowers the loudness of both channels together.
Presence: Controls the amount of negative feedback. Higher settings reduce negative feedback and give more distortion. Lower settings increase the negative feedback on the power supply and reduce distortion.


********Back Panel ************

Ground Switch: Places a capacitor between one of leads from the mains to the ground. (May not be hooked up)

ON/OFF; Controls power to the amplifier. Make sure the standby is "off" before switching on. If the tubes get fed full plate voltage (over 400v) without being warmed up first, there can be damage to the cathode part of the tube.

Standby; controls the high voltage power to the tubes. Has the effect of silencing the amp. Let the tubes heat up a few moments before disengaging the standby when first powering up.

Fuse: There are two fuses. One on the back panel and another under the chassis. The fuse on the back panel is the 'overall amp current' fuse and should be a slow blow 3A for 120v systems and a slow blow 2A for 220 systems. The other fuse is an extra saftey measure  just to protect the transformer and is a lower value (0.5A).

Speaker impedance: 4/8/16 Set this to the amp cabinet or speaker impedance.

Effects Input and output: This is a passive effects loop, There may be gain mismatch between the input of this jack and that of an effects pedal. Try it and see how it works. If you  are serious about having an active loop, you can buy or build a Dumbelator which will plug in here and will  have its own input/output into which the effects will plug.

PAB and OVERDRIVE switches on back panel: With the foot pedal unplugged, these switches control the preamp boost (which disengages the tone controls for some extra gain) and the Overdrive channel (which adds gain and distortion to the clean channel). So, they would be "ON" when set to "Manual". When the foot pedal switch is plugged in, keep these switches on "Pedal" for correct function with the foot pedal.

**********Inner Potentiometers (trimmers)***************

FET INPUT TRIMMER: located on the board near the FET input. Adjust this to change the gain of your acoustic guitar plugged into the FET input.

OD TRimmer: Located closest to the guitar inputs on the rectangular board. Adjust for the lowest setting that will produce a good overdrive tone.

Phase input trimmer. Located closest to the power tubes. Used to balance the two sides of the phase inverter tube.

Bias Pot and Bias Points: Put a multimeter lead into the red and black jack and set the meter to millivolts. The reading will approximate the milliamp current draw of the tube. Set using the bias pot, set the value to an appropriate level for the tubes installed.

Tube types: The two larger tubes are 6L6. The three smaller tubes are 7025 or 12AX7.