We’ll see later how this design causes some issues in the circuit. These inputs also use non-shorting jacks, meaning that all channels are “on” regardless of which have inputs plugged into them. Not sure what the benefit is here – as plugging instruments and microphones into all six channels simultaneously without individual attenuation controls is unlikely to sound very good. While input jacks are marked “Microphone or Instrument”, the impedance of all jacks is exactly the same. The amp has a total of SIX input jacks over two electrically identical channels. Two Identical Channels With Six Non-Shorting Input Jacks! There is no real sonic benefit to this design at all – it was a design choice driven by cost-savings – either to compensate for a chosen power transformer that couldn’t support the tube complement or to save a few nickels by not having to add a cathode bias resistor and cathode bypass capacitor. It also gave ample opportunity for noise and interference to be introduced. This unconventional design caused the amplifier to have an abnormally long warm-up time – usually between 60-70 seconds. Simplified illustration of how the 6L6GB power tubes are biased via the filaments of the two 12AX7 tubes.
#AIRLINE GUITAR AMPLIFIERS SERIES#
What’s more – one of the two 12AX7 tubes that bias the power tubes is located on a different chassis! They were wired in series from cathode pin 8 of the two 6L6GB tubes through pins 4 & 5 of the first 12AX7 tube, through the unshielded connector cable running to the second chassis, through pins 4 & 5 of the second 12AX7 tube, and then to chassis ground of the upper chassis, which was grounded to the lower chassis via the connector cable. The cathodes of the 6L6GC tubes were connected to ground through the heater pins of the two 12AX7 tubes! The heating of these tubes (roughly 12.6v x 2 = 25.2v) were what provided bias for both 6L6GB output tubes. The output stage of the Airline 9005 has quite a unique design – the 6L6GB power tubes did not have a fixed bias OR a cathode bias. The two metal chassis are connected by a shielded cable carrying the audio signal path and by a multi-pin connector carrying high DC voltage, vibrato connectors, and part of the cathode bias design. The lower chassis contains the power supply, the output stage, and the vibrato circuit. The upper chassis contains the inputs, the preamplifier, tone stack, and vibrato controls. The first unique aspect of the design is that the Airline 9005 amp has two chassis. The schematic for the Airline 9005 amplifier reveals several unique design features: 1. The upper chassis was moved from the back of the amp to the front.The owner said it was not working and wanted to see what could be done to bring it back to working condition. I recently got one on the bench – however, it had been re-cased into an ill-fitting, pleather-covered, plywood and MDF board case. This is the Airline 9005 amp as I received it – having been installed into a new cabinet. An image of an Airline 9005 in pristine original condition I found on a selling site.
The original case for the amp looked super sweet. I’ve seen examples with two 12″ speakers and one 12″ speaker.
The Airline 9005 guitar amp was sold by Montgomery Ward’s in the early 60s.
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