one of them fully up (or down!) diminishes
the effect of the others. Should you want
more “push” or “drive” from the preamp,
try setting all 3 tone controls at the 3
o’clock position and adjust the EQ from
there. This adds more touch sensitivity to
the preamp. Find a drier tone and feel by
setting the tone section to 9 o’clock and
adding back tone as needed.
NOTE: The S50 preamp design is much like the Fender
Blackface era amps; more linear than the Marshall or
earlier Fender Tweed designs. We added some gain
options including a second high gain preamp stage
typical of the “Metal“ amps via the Pull-Boost feature
(footswitchable) and also the inovative PREBIAS
control which changes the overall gain structure of the
preamps stage by increasing the supply voltages.
The power amp stage is a unique output design we
‘borrowed” from Aspen’s famous Black Plexi paneled
Red Park 50 amp made in the mid 60’s during
Marshall experimental period. The Park’s unique
output transformer is a complex design with many
interleafings and similar to Hi Fi designs...ver y
interactive to the players touch. To our knowledge,
this is the first time these designs have been
combined in one amp.
The Presence Control
This control interacts with the S50 power
amp stage, changing the high frequency
response. It alters the feedback loop of
the power tubes. It adds highs to the
power stage, making it noticeably brighter.
Use more Presence for an acoustically
dead room, and less for live rooms.
The Reverb Control
Our tube driven long spring Accutronics
Reverb is deep and harmonically rich and
runs in parallel to the signal path so it
doesn’t sap highs as you crank it up.
The Power Amp Stage
Your Soul-o 50 Class A/B design can use
any one of nine different matched Duets
from our EL34/6CA7 and 6550/KT88
family of Power Pentode (or Tetrode) tube
types currently available from our GT
catalog, and in any of the 1 to 10 power
ratings. Changing power tubes will require
a new bias adjustment unless you are
replacing tubes of the same tube type with
the same rating. A change in the type
and/or rating of your power tube can make
a dramatic difference in your tone and
power.
For example, the S50 output power can
range from about 50 watts RMS with a low
number EL34R up to almost 80 watts
R M S with our KT88sv! Rebiasing is
required with all tube changes unless you
are usg the same type and rating in the GT
system. Unless ordered other wise, your
S50 amp will come equipped with a Duet
of our ver y best, the GT34Ls @ 60+ RMS.
Speaker Impedance Selector
and Speaker Output Jacks
The
S50
custom
wound
output
transformer has 3 secondar y windings for
selection between 4, 8, and 16 ohms
speaker loads. Always tr y to exactly
match the speaker load with the
impedance selector for maximum power.
Use the #1 speaker jack for just one
speaker (or as a combo amp). The #2 jack
is for adding a second speaker.
NOTE: The #1 jack has shorting circuitr y which turns
the amp off if there is no speaker connected so you
will hear NO sound from jack #2 if #1 is not in use.
GT’s Parallel FX Loop w/ Mix
This is the most tonally transparent FX
loop possible. When properly set, our loop
allows you to use any digital or analog FX
unit mixed in parallel with your original
preamp signal with no sacrifice of tone!
Most loops are the Series type, so the FX
unit is placed is between the preamp and
power stage...so the sweet, fat, tube
preamp signal is changed into a thin,
wimpy transistor signal. We call this
“the
tone sucking transistor FX l o o p
syndrome”
, and the GT’s parallel loop
with Mix control is the cure!
To Operate:
Set the FX unit 100% Wet and 0% Dry.
Now, you can use the Mix control on the
S50 rear panel to adjust the desired level
of the FX box. Usually, best results
happen with a Dr y:Wet ratio of 98%:2%.
Another cool trick is to insert an ordinar y
foot controlled volume pedal in the signal
path returning from the FX to the “INPUT”
of your S50 FX loop. This allows you to
gradually increase or decrease the FX l e v e l
without changing the amps volume!
Soul-o Speaker Cabinets
GT cabinets are “tuned” for guitar playing.
They are fundamentally diff e rent than most
other guitar cabinets on the market today.
We use 3/4” solid core plywood for the
top, bottom, back and sides but a
lightweight 5/8” plywood speaker baff l e
b o a rd. We slant the baffle board upwards
for better projection, and “tune” it’s
resonance to optimize the tone for guitar.
This design produces tighter bass notes
avoiding the common “Big E String Mush”
syndrome.
GT guitar cabs come with our exclusive
“Classic Clone”, USA made speakers.
These are made to our specifications,
inspired by our favorite 60’s era speakers.
www.groovetubes.com
Groove Tubes
LLC
Custom Shop Products
1543 Truman Street, San Fernando, California 91340 USA, Tel 818-361-4500 Fax 818-365- 9884
www.groovetubes.com
©2004 Groove Tubes LLC. All rights reser ved. Groove Tubes, the “GT-in-a-circle” logomark, Groove Tubes Custom Shop, Groove Tubes Custom Shop Products, Soul-0 and S50 are trademarks and
service marks created and owned by Groove Tubes LLC. All other marks are the property of their respective owners. All specifications subject to change without notice.
S50 Technical Specs:
Input(s):
1/4 “ phone jack front and rear
Input Level:
-10 dB nominally
FX Input level:
+4dB dB nominally
Preamp Tube Section
V1 - 12AX7
V2 - 12AX7
V3 - 12AU7
V4 - 12AT7
V5 - 12AX7 or 12AT7
V6 & V7 - EL34/6CA7 or 6550/KT88
Power Section:
50 watts RMS Class A/B type @ 4, 8. 16 Ohms
Optional EL34 Family types:
GT6CA7GE, GTE34Ls, GTEL34R, GTE34R2,
GT6550C, GT6550R, GT6550R2, GTKT88SV,
GTKT88C and GTKT88C2
AC requirement
: 117 VAC Standard
100 VAC (special order), 230 VAC (special order)
H.T Fuse:
1 Amp Slo-Blo
AC Fuse:
100-120VAC@3A Slo-Blo
230 VAC = 1.5A Slo-Blo
Weight:
S50-12C Combo 42 lbs.
S50-15C Combo 44 lbs.
S50 Top 32 lbs.
Options:
Footswitch (Boost & Reverb) with 25’ cord
Slip Cover with pocket for footswitch and cables
Soul-o 50 Amplifier
Operators Guide
SIGNAL
PATH
EL34
6CA7
6550
EL34
6CA7
6550
V5
V8
V7
V4
V2
V1
V3
FRONT PANEL
INPUT
OUTPUT
XFMR
POWER
XFMR
SECRET GAIN
TRIM POT
for non boost
mode only
TUBE LAYOUT
V1 - 12AX7
V2 - 12AX7
V3 - 12AU7
V4 - 12AT7
V5 - 12AX7 or 12AT7
V6-V7
EL34/6CA7/6550
Speaker Cabinet Options
S50-12C
- 1 x 12” speaker
S50-15C
- 1 x 15” speaker
EX112
- 1 x 12” speaker
EX210
- 2 x 10” speakers
EX212
- 2 x 12” speakers
EX410
- 4 x 10” speakers
EX115
- 1 x 15” speaker
Rear Panel Features
