Puresound A30

Need some advice from you clever peoples here.

Got a puresound a30 that have a kt 88 valve that I now know worked intermittently. Anyway it took out both cathode resisters on the board. I replaced these with the same value types (shiny gold things) and changed the kt88 and had it running today for 4 hrs with no problems. They only thing that worries me is that they get very hot is this normal.

Below is the pics with new 10w 390ohm resisters fitted.

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Calling @murrayjohnson

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First of all 390R isn’t the cathode resistor value in an A30 although it might be the value in the Chinese (Bewitch) version.

With the correct bias resistance of 255 Ohms, 560 & 470R in parallel, the bias should be about 40V and you’d expect dissipation over that resistor of about 6W.

It does sound as if you need to double check the output valves.

pm me if you need me to look at it or test the o/p valves you’re using


Those resistors need to be mounted on a suitable heatsink in order to achieve their rated dissipation. At 6W they will still need some heatsinking to keep the case temp down to stop charring of the PCB.

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Up and running ! Huge huge thanks to Guy for the parts and the tutorial. Couldn’t of done it without him.

Top notch . :+1:



Terrific result, was this one Ricks?

It’s too good for Ricks system. :joy:


…couldn’t have….


:+1: :joy: