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The Gibson EH-100 model. There were a few different versions of this amp from about 1936-1940 I believe. This one in stained mahogany is a 1940 version. A cool feature of this amp is that the top and bottom section are detachable. The bottom section is the amplifier and top section holds the speaker. The Gibson logo in the corner is screen printed on. The EH-100 was advertised as

The Gibson EH-100 model. There were a few different versions of this amp from about 1936-1940 I believe. This one in stained mahogany is a 1940 version.
A cool feature of this amp is that the top and bottom section are detachable. The bottom section is the amplifier and top section holds the speaker. The Gibson logo in the corner is screen printed on. The EH-100 was advertised as “the” amp for Hawaiian electric guitar.

Some modern caps are visible in the pic but other than that this thing was all original. For some reason a previous tech started this repair and then abandoned it. The power supply was recapped but the amp sounded terrible. This amp runs two 6V6GTs in push pull so they should be running at an equal current draw. When I got the amp one tube was at 70mA and the other was 21mA! Coupling caps linking the phase inverter and the power tube grids were replaced and the bias was evened to 41mA per tube. This was still too hot though so the cathode resistor was adjusted to reach a nice bias of 20mA at 363Vp. Drifted resistors and a few cathode bypass caps were replaced and it sounded clean again.

Some modern caps are visible in the pic but other than that this thing was all original. For some reason a previous tech started this repair and then abandoned it. The power supply was partially recapped but the amp sounded terrible.
This amp runs two 6V6GTs in push pull so they should be running at an equal current draw. When I got the amp one tube was at 70mA and the other was 21mA! Coupling caps linking the phase inverter and the power tube grids were replaced and the bias was evened to 41mA per tube. This was still too hot though so the cathode resistor was adjusted to reach a nice bias of 20mA at 363Vp. Drifted resistors and a few cathode bypass caps were replaced and it sounded clean again.

Long speaker cable allows the speaker to be placed up to about 3

Long speaker cable allows the speaker to be placed up to about 3″ away from the amp.

Three inputs and one volume knob. The volume knob controls mic volume only. Instrument volume must be controlled from the instrument.

Three inputs and one volume knob. The volume knob controls mic volume only. Instrument volume must be controlled from the instrument.

IMG_0794 IMG_0829

Gibson EH-100 schematic

Gibson EH-100 schematic. In these old schematics M means K, as in a 500M resistor is 500K. Resistances in megs are listed as MEG, as in the 2MEG grid resistor for the 6SQ7 tube is 2,000,000 ohms.