The AC-15 Chassis - 1960 Model








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© 1998 - 2017 The Vox Showroom, all rights reserved. No use on online auctions, eBay or Reverb.
This is an example of a JMI Vox AC-15 chassis from 1960.

Three ECC83, one EF86, one ECC82, two EL-84, and one EZ-81 rectifier tube make up the tube complement.

Looking at the photo at the top of this page, the power transformer is located at left, the power supply choke is at center right, and the output transformer is at right. The locations of the transformers at either end of the chassis balances the weight of the chassis.

The ingenious design of the JMI Vox AC-15 chassis combines an anodized steel horizontal base section and an aluminum vertical control section.

The steel base of the chassis supports the power supply and output amp sections of the AC-15. The use of steel in the chassis base not only provides strength but also electronically isolates the high voltage (and hum producing) section of the power supply and output amp from the preamp area of the amp.

The aluminum vertical section of the chassis supports the preamp circuitry and control panel. The use of aluminum for the preamp area offers several benefits. Aluminum is less likely than steel to pick up hum and oscillations from the power supply and output amp setion of the amp, further electronically isolating the preamp from the power supply. Aluminum is significantly lighter than steel, but it is not as strong. Brackets mounted to the top of the power and output transformers strengthen and support the upper area of the aluminum section of the chassis.

The amplifier was neatly hand wired on tag strips. Top end WIMA "Tropyfol" capacitors were used throughout the preamp section. Even as these amps approach their fiftieth birthday, non-tube electronic failures in JMI Vox AC-15s are rare, a testimony to the high quality components used in construction of the amp.

Removing the upper back panel of the cabinet exposes most of the circuitry in the amp for service convenience.

The AC15 amp pictured on this page featured a Celestion "Alnico Blue" speaker.

The picture at bottom left shows the manufacturer's date stamp on the output transformer. It reads "30 AUG 1960."

The entire chassis is mounted to a baltic birch plywood "slider board." Once the upper back panel is renoved from the amplifier cabinet, the chassis slides out of the cabinet like a drawer.




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Photos and editorial content courtesy Gary Hahlbeck, North Coast Music


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