The Gibson EH Series was among the very first amplifiers ever built in history. It dates from 1935, just about four years after the electric guitar was invented. The EH Series amplifiers came with a lap steel at the time.
The Gibson EH185 tubes are 6L6(2), 6N7(3) and one 5U4. It's got tone controls for Bass and Treble and separate volume knobs for each channel (instrument and microphone inputs).
This amplifier is very unique in many ways. Its cabinet has a cover that needs to be removed in order to access the control panel on the chassis - that can also be removed from the cabinet. According to its original operational manual, the EH185 produces a better low end when the chassis is off the cabinet because there is more space for the cabinet to resonate as well as eliminating the “tube rattle”. Another curious fact: it employs a Field Coil Speaker very similar to a common speaker however it uses an electromagnet instead of a regular magnet - and that is a big part of its sound.
Since the EH185 was originally designed to be a lap steel performer amplifier, it has two inputs. One instrument input for the lap steel that used to come with the amp and a microphone input that the performer could sing into while playing. The interesting fact about it is that you get the best tone out of it by plugging the guitar into the microphone input using the difference in impedance as an extra source of gain. Naively, Gibson 'warned' their users on the manual saying it was possible to plug an instrument to the microphone input of the amp but with caution. Too much volume could 'distort the sound'. What was considered wrong in the 30's nowadays is this little amplifier's greatest asset. It delivers a lot of gain while still remaining a relatively soft sounding amp.
Producer/Mixer Jay Baumgardner says that the EH185 is one of his favorite amps out of his big collection - “Its tone is very distinctive, there's no other amp that sounds alike that because of its speaker and microphone input circuitry” he says. In the 40's the EH185 was used by jazz guitarists like Charlie Christian. Nowadays it is on Josh Holme's set up and has played a big part on Queens of the Stone Age's guitar tones.