750pF

1971 SUNN SCEPTRE with MID BOOST

drawn by Steve Luckey, 07/01/2006
Reverb 1K / 2W
in out
circuit 680 / 2W
D D C C B B
270K/.001uF
Tremolo 6550 3
488vdc blue/wht
V4
12AX7 circuit
MID BOOST (A)
270K 1.5M 12pF
47K
1W 0.1
100K 100K 1K 4 490vdc
5
BRIGHT
16 (yel)
0.01 470pF 270pF 6 V3A V3B 100K
1 8
grn/wht 8 (orn)
270K/.001uF V1A X Y 20M 8 ohm
V1B TREBLE
12pF
7
2
E1 1Ω 60mv
red 4 (brn)
1 6
Located on 8
A 4 ohm
47K
2
500K
7 R/T PCB
56K 250K 220K E2 1Ω 60mv grn
9
0.1 3
VOLUME 1.5 100K 8 blue 0 (blk)
NORMAL 3 8 1M
47K .022 BASS 5
4 490vdc
.022
100K 100K
6AN8 47K 0.1
1K
Output Transformer
.22 1W
150K 1.5K 250uF 1.5K 3 V5 Woodward-Schumacher
CONTOUR
25K 680
390pF 6550 488vdc 28-1360
606108 (1971, week 8)

MID BOOST (B)

47

Power Transformer
Woodward-Schumacher
28-2360
606103 (1971, week 3) GZ34 Fluke 87V True RMS DMM
3 AMP 430 VAC
6 V6 These voltages measured after 1 hour warm-up with line voltage at 115VAC. Located on R/T PCB
8 Bias pots were adjusted for 60mv at bias test jacks on cathodes of V4 and V5.
SLO BLO
1K
LINE A B C D F
2
430 VAC 504 VDC 498 VDC 392 VDC 299 VDC 262 VDC +22 VDC
POWER
SWITCH
4 E1 E2
with -60 VDC -60 VDC 1K / 2W
indicator
5 VAC
6.8K / 2W 6.8K / 2W 10K / 2W BIAS BIAS 1K / 2W
10K 10K

6.3 VAC 20uF @ 20uF @ + + 22V 1W

NEUTRAL 20uF 20uF 20uF 50uF 18K 50uF 18K 50uF 50uF 1000uF
to all 600V 600V + + + Zener
heaters
 D C F

Reverb Reverb 4.7K

10uF
.005
Input Gibbs Output +
12AU7 Reverb Spring 470K 750pF Reverb Output
100K 4.7K
Assembly 10K to
REVERB V3 pin 8
.05
V2-A 6 V2-B 1 2.2M
470K .022 .022
Reverb Input 2
7 Q4
from V1 pin 6 REVERB 2N2923

8 3 FOOTSWITCH
.005 220K
15
220K 2.2K 47K 1.5K 1uF

F F F F
Original optoisolator
SIGMA DATACEL
301 R2-12

4.7K 22K Tremolo Output

2uF
+ +
10uF 1.5K to
points “X” and “Y”
DEPTH
680K 3.3K 25K 1.2K
Q1
2N2923
1uF 2uF 1uF 10uF Q3
+ + + Q2 +
2N2102
2N2923 Original optoisolator failed.
BC141C
Replaced with Vactrol VTL5C1
2.7K 1.8K 1.8K 15
220K 22K
1OK
25K 25K 25K
15 TREMOLO Original was 1.2K. Replaced
FOOTSWITCH with 10K to work with Vactrol
TREMOLO SPEED