My universal Concertina boards. They stand vertically near tube sockets, connected by short wires and resistor, for better power dissipation. The first tube can be either pentode or triode. The second triode is directly coupled through a voltage divider shunted by a cap. In cathode of the 1'St tube can be either LED, or a resistor shunted by a cap. Either grid stopper, or a cap can be used on the first grid. Also, there are pads for input LDR attenuator.
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I'm weird. I actually still like the floating paraphase although it's not as good, you get gain and phase splitting in one go.
I use it too, although at lower power it has more distortion than a 6sl7 gain/cathodyne.
I have a LTP too with ECC99 with pentode current sink at 30 Ma... with 430V B+ and -125V at pentode. It is an attempt to better the 6sn7 with transistor current sink LTP. Not really-better if only for a little reduction in IMD.
Oh well, if we're pimping universal PCBs, here's my gain stage + cathode follower or phase inverter PCB (for guitar amps, but equally suited to hi-fi)! 😛
The Valve Wizard
I did not measure; it was enough to drive 12BQ6 tubes.
You can set working point by a voltage divider R107/R108, and see for yourself on a load line depending on the tube that you use and B+ that you supply.
The board is universal, any tube with any socket and pinout can be soldered by vires. Also, since it is not flat, cooling of resistors on it is the best.
I have measured my 6F12P amp/cathodyne few years ago.
The results are attached. With 380 V supply voltage the clipping begins at some 140 Vpp.
Thanks Arto, i had already tried this with 6P36S output and very good and want also to create my own driver PCB using this good tube and try other output tubes.
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