The Dumble Style amp

Few amp makers shroud themselves in mystery as much as Howard Alexander Dumble. And few amps generate as much interst into the minute details of the evolution of his circuits from the original reworking of Fender circuits to his Overdrive Special, Steel Stringer and other amps he makes.

I can't really get a handle on the total production volume he has produced, maybe several hundred at most. Let's face it, he's just one guy. He gets all his money up front and its big money at that, well into 5 figures. Then you wait a year, maybe two or three for your amp. That is, if he agrees you are worthy.

However, there is no denying the sound. Larry Carlton, Robben Ford, Stevie Ray Vaughn, David Lindley...and on and on. With demand being high and supply low (unless you have about $25 grand or so to buy one on the used market) it's no wonder several companies have been offering their versions of the Dumble style amp. Fuchs Audio, Two Rock amps, Carol Ann and others. They are expensive at well over $3K. But they are complex amps with a lot of variations and building one requires attention to detail and good componenet choices.

I have built several over the past few years. Each one used the same basic ODS (Overdrive Special) circuit and I like to build them to support 6V6 power tubes or 6L6 tubes. That gives a spread of 22 watts for the 6V6 up to about 40 for the 6L6 tubes. Of course you can add more power tubes and bring it up close to 100 watts but frankly its just not needed unless you are playing a big venue.

dumble 2

Front panel of one of my home brewed ODS replicas. I use a larger sized Hammond Chassis with a steel cage cover and mount a bottom plate with feet and a handle on top. This particular amp has a footswitch that controls the Overdrive/clean circuit and the PAB (pre amp boost) circuit as well as the front panel switches you see here. I have this one fit up with 6V6 tubes but switching to 6L6 tubes is just a matter of a rebais. The power and output transformers are set to handle either. I sell this amp for $1300.




dumble 1

You always remember your first...this was my first one. Not so pretty to look at but man did it sound good. Sold it to a local friend and musician who uses it to gig with locally and recorded a CD with it and one of my Trainwreck replicas. This one currently drives 6L6 tubes and a nice set of Vintage NOS preamp tubes. I added a footswtch for the overdrive/clean circuit for him.





Here is a peek at the inside. The heater wires run over the tube sockets for low noise and the preamp tube wiring is layed out carefully to avoid crosstalk interference. Way in the back along the far end of the chassis you can see the bias supply and power supply diode board. The closer in is the power supply capacitor board. In the forground is the preamp component board.






An overview of the inside. There is a lot going on in these amps and getting the lead dress correct goes a long way to a quiet and great sounding amp. I always build these in stages being careful to cross wires at right angles, use shielded runs for long signal carrying wires, etc.







The preamp section of the circuit board. I build these myself. See that little blue box shaped thing in the picture? That is a variable pot that has a small screwdriver adjustable screw on the other side to let you tailor the overdrive channel gain to your taste. Its a way Dumble made his amps tweakable to each client. In later versions he added another small board to control the midrange sound and characteristic of the overdrive. This is known as the HRM (hot rubber monkey) version. I do not know why the monkey is hot or made of rubber.




power supply

Here is a shot of the power supply board and the capacitors that feed the amp. The big sprague atom blue caps are set up to provide the main ripple filter. See the big white power resistor at the top? That is there to take the place of a choke in the power supply. The other smaller caps feed the various phase inverter and preamp tube sections of the amp. The amp get a huge clean Fender tone abd a lot has to do with this power supply. Remember, Dumble started with the Fender circuits and modified them from there.





power tubes

The power tube end of the amp. Not a lot of uniqueness here but just good layout and attention to making a quiet amp. In later versions of his amps, Dumble would cover his circuit boards with a black epoxy goop to obscure the component use and values he employed. We amp builders are a crafty bunch.







Here is a more traditional chassis being built. This will be mounted in a head cabinet with the chassis hanging down. This amp is being built and will be for sale.








The backside shows the outside mounted bias points (the red and black mini jack looking things). I mount an adjustment pot on the chassis bottom reachable from the amp while still mounted in its cabinet. On the far right end of the chassis you can see a DIN jack for plugging in the footswitch control for OD/Clean and the PAB boost function.





Here is an inside view of the preamp board. You can see the switching relays mounted on the green boards near the pots. There is a separate power supply for this set of relays and they are totally silent when you use the footswitch or front panel controls. This is a great sounding amp- but then all the Dumble circuits I have built have been. Just remember to use the best quality tubes you can, it really make a difference in these amps.