| Retrodyne amplification |
| Presents: "The Pent-Ode to Joy" (with apologies to Schiller) |
The Mission:
6AU6 Pentode clean channel, 12AX7 'HiGain' channel, 12DW7 Phase inverter with Master Volume,
cathode-biased EL34EH's, power supply to use existing 'universal' board I developed for all new
builds. Power supply is centered around a JJ-brand multi-section can capacitor (40,20,20,20uF x
500V, plus lightly choked screen supply. All circuits are built on G10/Garolite, with filament and
ground wires on one side and the signal an PS elements on the other. All passives to be
point-to-part with as few short wires as possible! Plus beat Mark Lavelle to the punch in building a
new 6AU6A front-ended amp! Thanks for the tube and CD sampler, Mark!
6AU6 Pentode clean channel, 12AX7 'HiGain' channel, 12DW7 Phase inverter with Master Volume,
cathode-biased EL34EH's, power supply to use existing 'universal' board I developed for all new
builds. Power supply is centered around a JJ-brand multi-section can capacitor (40,20,20,20uF x
500V, plus lightly choked screen supply. All circuits are built on G10/Garolite, with filament and
ground wires on one side and the signal an PS elements on the other. All passives to be
point-to-part with as few short wires as possible! Plus beat Mark Lavelle to the punch in building a
new 6AU6A front-ended amp! Thanks for the tube and CD sampler, Mark!
The signal side of the boards. These boards have been built with lots of combinations of octal,
9-pin and 7-pin sockets. I can swap out the PI for a 'long tail pair' inverter etc. if desired. I added the
internal 'night light' as a gag for testing the chassis at a gig in a dark club. I only had to use coax for
the master volume grid circuit. I built the preamp section to test out a 6AU6-A pentode that
promised to be as powerful as the 6SJ7WGT's I have been using but with less microphony. This
chassis also allowed me to test my newest rev. of the 12DW7 driven concertina PI I've been
tweaking for a few years now. This one has a 1Meg pot as a pre-PI level pot more than a true master
volume, though it functions very well in a similar fashion. I wanted to avoid adding anything in the
EL34's grids which could sap dynamics and transparency.
The 12DW7 when biased right has a great shimmer from the 'AU' side and can swing a wild and
woolly 40 VAC(almost 80v p-p) The smooth onset of distortion makes 12AX7A versions of this circuit
sound shrill and buzzy in comparison. YMMV of course. But anything capable of 4x the current is
hard to argue with- and you only need 30 or so vac to drive EL34's quite nicely!
9-pin and 7-pin sockets. I can swap out the PI for a 'long tail pair' inverter etc. if desired. I added the
internal 'night light' as a gag for testing the chassis at a gig in a dark club. I only had to use coax for
the master volume grid circuit. I built the preamp section to test out a 6AU6-A pentode that
promised to be as powerful as the 6SJ7WGT's I have been using but with less microphony. This
chassis also allowed me to test my newest rev. of the 12DW7 driven concertina PI I've been
tweaking for a few years now. This one has a 1Meg pot as a pre-PI level pot more than a true master
volume, though it functions very well in a similar fashion. I wanted to avoid adding anything in the
EL34's grids which could sap dynamics and transparency.
The 12DW7 when biased right has a great shimmer from the 'AU' side and can swing a wild and
woolly 40 VAC(almost 80v p-p) The smooth onset of distortion makes 12AX7A versions of this circuit
sound shrill and buzzy in comparison. YMMV of course. But anything capable of 4x the current is
hard to argue with- and you only need 30 or so vac to drive EL34's quite nicely!
the night light in action
Circuit boards are mounted to chassis with silicon rubber washer
sandwich on the stainless steel machine screws. Tube sockets also
are mounted this way.
Time consuming but every bit of vibration reduced helps.
As run with a GZ34, plate volts are 385, Vs 362,
EL34's idling at 50 ma EACH. :-)
6AU6 has Vp of 175, Vs of 80, Vk 1.68v
PT: 300-0-300/ 150ma, 5V/3A, 6.3V/5A
Hammond 272FX or equivalent.
OT: 6.6K, 25W, 4,8 ohm outs, UL taps.
Sourced from Triode Electronics, Chicago IL.
Choke: Twin/Super/Pro size
output: 20W RMS clean, 29WRMS rippin'
works well into 2x12 cab with Silver Bell and Blue Dog ceramic 12's.
Pentode preamp doesn't care whether you hit it with single-coils or
humbuckers. Powerful punchy tone and lots of sustain & harmonics.
Way less noise than EF86 too!
sandwich on the stainless steel machine screws. Tube sockets also
are mounted this way.
Time consuming but every bit of vibration reduced helps.
As run with a GZ34, plate volts are 385, Vs 362,
EL34's idling at 50 ma EACH. :-)
6AU6 has Vp of 175, Vs of 80, Vk 1.68v
PT: 300-0-300/ 150ma, 5V/3A, 6.3V/5A
Hammond 272FX or equivalent.
OT: 6.6K, 25W, 4,8 ohm outs, UL taps.
Sourced from Triode Electronics, Chicago IL.
Choke: Twin/Super/Pro size
output: 20W RMS clean, 29WRMS rippin'
works well into 2x12 cab with Silver Bell and Blue Dog ceramic 12's.
Pentode preamp doesn't care whether you hit it with single-coils or
humbuckers. Powerful punchy tone and lots of sustain & harmonics.
Way less noise than EF86 too!
No copper was spared for shielding. The "Gain-E-ack" uses the 'E' tone control to great
effect! I wanted to develop a 'vintage' gain stage but with NO dang scooping of precious
mids. Why spend good money on premium pickups and then suck all the glorious
mids?!?! I'll never understand that... Anyway, here's the schematic to the "Gain-E-ack",
lots of ways to tweak to taste. Somebody send this to Sean Kilback :-)
effect! I wanted to develop a 'vintage' gain stage but with NO dang scooping of precious
mids. Why spend good money on premium pickups and then suck all the glorious
mids?!?! I'll never understand that... Anyway, here's the schematic to the "Gain-E-ack",
lots of ways to tweak to taste. Somebody send this to Sean Kilback :-)
Here's a live recording sound sample
