Well, time to put the spice and computer to bed and build the real
circuit. The pentode over a triode is not a new idea and it does work.
The trick is to get it to work correctly. I use an SRPP driver
stage in the power amps I build and also as the first gain stage in a
guitar amp I designed and built. This particular stage will pass a
perfect square wave from around 8hz to over 80Khz. It is quiet and
resists overload better then a single triode gain stage.
Bill Bittle
Tube amp tech at:
http://home.alltel.net/wbittle
robert casey wrote:
Been playing around in simulation with a SRPP
circuit using a triode on bottom and a pentode
up top. Reason for the pentode is so I can filter its
screen supply to get better power supply ripple
rejection. Otherwise it would be a triode
connected pentode. Simulations suggest that
I can get about 50dB power supply rejection with
the pentode with a well filtered screen supply.
Say the triode is half a 12AU7 and pentode a 6AU6,
or a 6AU6 triode connected on the bottom, and
another 6AU6 up top.
Made a new 3f4 spice model for the sub-mini
sharp cutoff pentode 5840 while doing this.
Don't think I'll use 5840's, but here it is.
************************************************** *********
*Vacuum Tube submini pentode (assumes K tied to g3)
.SUBCKT X5840 A S G K
*
* Calculate contribution to cathode current
*
*the number at the right end determines sharpness of knee
Bat at 0 V=0.636*ATAN(V(A,K)/9)
*the URAMP(V(S,K)/# mostly determines peak plate current, grid line
spacing nearly constant
*the number at the right end determines slope of grid lines (plate
resistance)
Bgs gs 0 V=URAMP(V(S,K)/28.8+V(G,K)*0.75+V(A,K)/4000)
*the exponent sets the linearity of grid line spacing, and big impact on
peak plate currrent
Bgs2 gs2 0 V=V(gs)^ 1.5
Bcath cc 0 V=V(gs2)*V(at)
*
* Calculate anode current, grid line spacing adjust and peak plate current
*
Ba A K I=2.585E-3*V(cc)
*
* Calculate screen current
*
Bscrn sc 0 V=V(gs2)*(1.1-V(at))
Bs S K I=0.550E-2*V(sc)
*
* Grid current (approximation - does not model low va/vs)
*
Bg G K I=(URAMP(V(G,K)+1)^ 1.5)*50E-6
*
* Capacitances
*
Cg1 G K 3.5p
Cak A K 2.9p
Cg1a G A 0.0155p
.ENDS X5840
************************************************** *******