The "Bedrock" Vox AC15TBR Prototype Amp - A Look "Under the Hood"





2_Footer
© 1998 - 2017 The Vox Showroom, all rights reserved. No use on online auctions, eBay or Reverb.
The AC15TBR prototype amp from Bedrock amplification featured an eight tube circuit.

The following chart details the function of each tube.

V1a
V1b
12AX7
Tremolo Oscillator
Reverb Receive Circuit

V2a
V2b
12AX7
First preamp gain stage
Not used

V3a
V3b
12AX7
Second preamp gain stage
Top Boost Tone Controls

V4a
V4b
12AX7
Reverb Drive Circuit

V5a
V5b
12AX7
Phase Inverter

V6
EL84
Output tube

V7
EL84
Output tube

V8
5Y3
Rectifier


Printed Circuit Boards and Chassis
The chassis was assembled into a rectangular steel pan that was fastened to the sides of the cabinet by four screws.

The circuitry was assembled on two printed circuit boards; one for the preamp and a second for the power amp. The tube sockets and controls were mounted directly to the printed circuit boards.

"Top Boost" Preamp
While designing the AC15TBR, Korg requested that Bedrock utilize the circuit from the"Top Boost" channel of the Marshall/Vox AC30TB(X) without modification. A close examination of the schematics confirmed that both amps had the same "Top Boost" preamp circuit.

Reverb Circuit
The reverb circuit for the Bedrock designed AC15TBR utilized a drive transformer. This transformer was not included in the reverb circuit of the Steve Grindrod designed AC15TBR from Marshall.

Power Amp Circuit
The power amp stage of the Bedrock designed AC15TBR used two EL84 tubes in the classic cathode biased, no negative feedback design from the original JMI AC-15.


"Bedrock" AC15TBR Specifications
Year
1995
Production Numbers
A few prototypes
RMS Power Rating
15 watts RMS
Channels
One with two inputs
Controls
Volume, Treble, Bass, Cut, Reverb, Tremolo Speed, Tremolo Depth
Tube Complement
Five 12AX7, two EL84, one 5Y3
Dimensions
23¼" wide, 16¾" tall, 10" deep


2_Footer

.................



The VOX Showroom!


Photos and editorial content courtesy Gary Hahlbeck, North Coast Music


Any and all material presented herein is protected by Copyright.
© 1998 - 2017 The Vox Showroom and North Coast Music, all rights reserved

The images and editorial content in this web site may not be copied or reproduced
in online auction sites such as eBay and Craig's List. Sellers may provide a link
to the Vox Showroom web site if they wish to refer to this copyrighted material.


URL: http://www.voxshowroom.com/uk/amp/bedrock_ac15tb_hood.html