pentode to triode

[space hopper]

Hi all

I am thinking of modifying the input of my KAT6550 from pentode to triode. The pre I am using has to much gain. It worked pretty well with the quad 2’s I used with it before but now with my 6550 the pre’s volume control is severely restricted. I have tried putting a potential divider on the input of the 6550 but it sounds a little ‘’muffled’’ to my ears. I have found a section in the Morgan Jones Valve Amplifier book which recommends the above mod.

Based on the steps outlined by Morgan I intend to do the following:

1) disconnect C4/5 and R6/7

2) connect grid 2 to the anode

3) change the feedback components (divide the resistance and multiply the capacitance by 4)

Morgan states that the cathode bias resistor may need to be recalculated?

Any thoughts on this would be much appreciated