BLUES JUNIOR
SPECIFICATIONS
Type
PR 295
Input impedance:
1M ohm
Power output:
15 Watts R.M.S. @ 5% T.H.D
Rated load impedance:
8 Ohms
Speaker compliment
One 8 ohm 12" Eminence,
replica of Jenson P-10
Dimensions:
Height:
16
inches
(41 cm)
Width:
18
inches
(46 cm)
Depth:
9-13/16 inches
(25 cm)
Weight:
31 lbs.
(14 kg)
THEORY OF OPERATION
J1 is a high-sensitivity input with an input impedance of about 1M
Ω
. V1B is the first gain stage
which also contains the "FAT" switch. The FAT feature is activated by grounding the node
between bypass capacitor C3 and R9. Via the FAT switch (S1) or the optional footswitch, the
junction of R52 and R54 can be grounded. With zero volts applied to the gate of Q1, the JFET
will essentially ground C3, activating the FAT feature.
The output of V1B couples to the VOLUME control (R7). The VOLUME control is actually a
preamp overdrive control that adjusts the level of distortion. C2 attenuates high frequencies
and C1 attenuates low frequencies at high distortion settings. This takes the edge off the
distortion and prevents the speaker from flapping. V1A provides a gain of about 40, and drives
the tone control circuitry. After the tone controls, the signal is fed to V2B, which drives the
MASTER volume control (R41). From the MASTER volume, the signal splits to feed the power
amplifier and the Reverb.
U1A makes up a typical solid-state reverb drive circuit. U1B is the reverb recovery or sense
circuit, which drives the REVERB control (R51). The reverb signal is summed with the dry
signal at C6, which couples to the input of the Phase Inverter (V3).
The output tubes (6BQ5/EL84) are arranged in a push-pull configuration that will produce
fifteen (15 ) watts R.M.S. into eight (8) ohms @ 5% THD, 1kHz.
The output bias is derived from the -15Vdc supply. The voltage divider at R31 & R37
determines the bias voltage (-10.7 Vdc). C14 filters the ripple to 1mV or less.
