Croft 25 Cathode Follower?

[fiddlemaker]

The output valve stage needs to be reconfigured from a common cathode circuit to a cathode follower implementation.

The anode load resistor has to be moved to the cathode plus a B+ connection made to the anode (I fit an anode stopper resistor to ensure complete stability).
A blocking capacitor has to be fitted in the grid connection from the volume control and a suitable bias network added.
The cathode to heater rating of the valve needs to be checked against the new bias voltage to ensure safe operation.

The output impedance is reduced considerably, by a factor of 7-10 times depeding on the valve type.
The only downside is the loss of gain that the output stage was originally providing, usually around 6dB.

Many thanks, Alan. I've sent you a PM.

[fiddlemaker]

I could not find any info on the output impedance of the 25, 25R or 25RS. It will be high as with all valve pre-amps which is why the 7R has such high input impedance.

Really, for the sake of removing one not very large box I'd stick with the Croft Monos, they're designed to work optimally together. The other option is to sell the lot and go to an all solid-state integrated. That way you'd ditch two boxes. Never any problem to sell Croft, someone will have your arm off for it.

Well, I tried a couple of alternative power amps, and decided that the Croft Monos are going nowhere. Took a comparison to make me appreciate again just how great they are.