Dumble Amplifiers - Circuitry

Circuitry

The circuitry varies somewhat between individual amplifiers, as each one was built and voiced for a specific player. Amplifiers built around the same time tend to share some of the same circuitry and component values. However, several amplifiers were later sent back to Dumble to have their circuitry updated.

Part of the characteristic sound of Dumble amplifiers is alleged to come from Dumble's choice of parts:

• the type of capacitors used in the tonestack and in the overdrive stages
• the type of plate resistors
• the output transformer
• the lead dress, and the use of shielded wire.

Dumble amplifiers are built on eyelet boards . The chassis is made of aluminum.

All Dumble amplifiers operate using vacuum tubes. Overdrive Specials use 12AX7 tubes in the preamp and 6L6 tubes in the power amp in older models. A few Overdrive Specials, notably #167 and #183, were equipped with EL34 tubes in the power amplifier section. EL34 tubes are associated with a more "British" or "Marshall" sound while 6L6 tubes are associated with a more "American" or "Fender" tone.

A separate "Dumblelator" buffered effects loop (a cathode-follower output with a triode gain stage for recovery) is recommended for using effects processors with a Dumble amplifier.