Vermes
Advanced Member level 4
It is a stereo full tube (2x18W) guitar power amplifier, adapted to be mounted in a 19” rack. Housing height is 2U. The construction is more simple than similar devices from Marshall or Mesa. It is based on a typical application for EL84 tubes in AB class and a typical paraphase inverter with cathode coupling based on ECC83. All that was doubled. Each of the power amplifiers has a separate power supply and thus can operate as a separate device. Only glow system is common, what means that all the tubes glow together simultaneously, no matter if one or both channels operate at once.
Presented device can operate with guitar speakers of any normal impedance such as 4/8/16ohm. Selection of impedance can be done via switches on the rear panel, separately for each channel. All I/O sockets are on the rear panel. Front panel is equipped with power switch, anode switches for each channel or standby, controls for those switches and Master/Volume knobs separately for each channel. Due to the fact that the system does not have an initial degree, the M/V knobs adjust the signal between the inverter and power tubes. Placed in that position M/V makes it impossible to apply a typical presence regulator in feedback.
Housing was removed from a fabric Chinese device SPL500. Plate used for that cheap device forced using rectangular pads visible in pictures (with inscriptions: inputs and outputs) for the sockets, because otherwise it would be impossible to screw them. In addition, on the rear panel, there is a low-speed 12V fan from a computer power supply blowing warm air outside.
List of components:
- SPL500
- EL84 x4 + ECC83S x2
- output and supply transformers
Pictures:
Schematic:
Link to original thread - Stereofoniczna w pełni lampowa końcówka gitarowa 2x18W w racku 19"