All of you keep me thinking, Thanks!.
I generally do not like Beam Power operation, I normally use UL or Triode wired modes.
Chris Hornbeck's suggestion, and the circuit in tubemax's Post # 30, got me thinking.
So yesterday, I tried that.
First with a RCA labeled 12AT7/ECC81 that said 'built in Germany' (yes it has the really bright filament at turn on); and a JJ KT66.
I was using the 900V IXYS current source as the 12AT7 plate load.
I already had the KT66 wired for UL. So I reconnected the screen from the UL tap, to a B+ point.
But I did not want to have to re-calculate the 12AT7 un-bypassed cathode resistor (because of DC from the feedback resistor), so I used a motor start capacitor in series with the feedback resistor to the 12AT7 cathode.
That means the gain is open loop at very low frequencies; but I am not planning on using signal sources that have Vinyl 3 Hz record warps, Telarc 6 Hz canons, and 32 foot organ pipes, with that amplifier.
I also tried it with a JJ ECC82/12AU7, with the lower gain versus the 12AT7; which changes the open loop to closed loop ratio.
So far, the amplifier has exceeded my expectations of such a simple circuit, and with a circuit that uses Beam Power mode.
Kudos to all who keep giving me ideas.
I generally do not like Beam Power operation, I normally use UL or Triode wired modes.
Chris Hornbeck's suggestion, and the circuit in tubemax's Post # 30, got me thinking.
So yesterday, I tried that.
First with a RCA labeled 12AT7/ECC81 that said 'built in Germany' (yes it has the really bright filament at turn on); and a JJ KT66.
I was using the 900V IXYS current source as the 12AT7 plate load.
I already had the KT66 wired for UL. So I reconnected the screen from the UL tap, to a B+ point.
But I did not want to have to re-calculate the 12AT7 un-bypassed cathode resistor (because of DC from the feedback resistor), so I used a motor start capacitor in series with the feedback resistor to the 12AT7 cathode.
That means the gain is open loop at very low frequencies; but I am not planning on using signal sources that have Vinyl 3 Hz record warps, Telarc 6 Hz canons, and 32 foot organ pipes, with that amplifier.
I also tried it with a JJ ECC82/12AU7, with the lower gain versus the 12AT7; which changes the open loop to closed loop ratio.
So far, the amplifier has exceeded my expectations of such a simple circuit, and with a circuit that uses Beam Power mode.
Kudos to all who keep giving me ideas.
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