“CUSTOM” VIBRASONIC
THEORY OF OPERATION
STEEL CHANNEL
J1 is the high sensitivity input and J2 is the low sensitivity input. The input is fed to V1A, which proveds a gain of
about 42. The output from V1A drives the Treble (R7), Mid(R9), and Bass(R7) tone controls, then feeds the Volume
control (R10). When engaged, the SWEET switch connects C5 to the wiper of the VOLUME control. This provides a
boost in the high frequencies. The “Sweet” feature is most noticeable at lower volume settings. The signal then
feeds to V1B, which provides a gain of about 66.
GUITAR CHANNEL
J3 is the high sensitivity input and J4 is the low sensitivity input. V2A contains the FAT switch which boosts the gain
mostly at lower and mid frequencies. V2A drives the tone controls, and the Volume control (R21) feeds V2B.
V1B and V2B share the same cathode resistor (R23) and bypass capacitor (C11). The output of the Steel channel
(V1B pin 6) sums with the output of the GUITAR channel at V2B pin 6. From that point the signal follows two paths.
One to the reverb drive stage (V3). The other through R32 to summing amp V4B.
REVERB
V3 (12AT7) provides a gain of about 33 to drive the reverb transformer. V4A is the Reverb recovery or sense stage.
The Reverb control (R29) determines the amount of reverb signal that is summed with the dry signal at V4B. Via the
footswitch, the Reverb can be disabled by grounding the signal at the node between R30 and R74.
VIBRATO
V5A is a low frequency oscillator. The
Speed
control (R56) varies the oscillation frequency. V5B is the Neon Lamp
driver. The lamp flashes faster or slower based on the position of the Speed control (R56). The brightness of the
neon bulb is sensed by the LDR (Light Dependent Resistor). The LDR connects to the
Intensity
control (R64) which
varies the amount of low frequency modulation applied to the input of the Phase Inverter(V6).
POWER AMPLIFIER
The output from V4B feeds the Phase Inverter(V6), which is a classic style split-load type, used without feedback.
The output tubes (5881/6L6WGC) are arranged in a push-pull configuration that will produce 85 watts minimum into a
four(4)
Ω
load at 5% THD.
PARTS LIST
PRINTED CIRCUIT BOARD ASSEMBLY
QTY PART # DESCRIPTION REFERENCE DESIGNATION
1
049266
PCB ASSY CUSTOM VIBRASONIC ALLV
(STUFFED)
3
037805
CABLE RIBBON 6CKT 2-1/4”
1
031069
CAP AE RDL 10uF 100v 20%
C37
5
028465
CAP AE RDL 22uF 25V 20%
C6 C11 C14 C27 C28
1
036954
CAP AE RDL 22uF 63V 20%
C36
3
024819
CAP AE AX 22uF 500v 20%
C32 C33 C34
1
031040
CAP AE RDL 100uF 100V 20%
C35
2
013638
CAP AE AX 200uF 285V 20%
C30 C31
2
025979
CAPCD 50pF 1KV 10%
C5 C10
1
031780
CAP SLVR MICA 150PF 300V
C7
1
007029
CAPCD 220pF 1KV 10%
C38
1
020917
CAPCD 250pF 1KV 10%
C2
1
020842
CAPCD 500pF 1KV 10%
C13
1
047065
CAP PFF RDL .0015uF 100V
C16
1
037666
CAP PFF .001 uF 400v 10%
C20
2
024823
CAP MPF RDL .01uF 400V 10%
C25 C26
