Converting Kit/Kat6550 and Kit/Kat34 Rectifier from 5U4 to 6D22S

[Richard]

Part 2 - Construction


Parts required;

2 off 6D22S or EY500 valves - 6D22S are cheaper!

2 off B9D Magnoval valve bases preferably ceramic, top or underside chassis mount.

2 off ¼” or 6mm valve top cap connectors ideally ceramic types.

1 off ¼” or 6mm rubber grommet.

About 30cm/12” of preferably PTFE insulated wire.

Valves bases and top cap connectors are available from various distributors and of course the well-known auction site!


1) Obviously power down first and the usual caveats apply about knowing your mains voltage and plus-or-minuses!

2) Remove the 5U4Gs

3) Disconnect the wiring from the valve bases, noting which are heater (purple) wires, which are transformer HT (black) wires, and which is DC HT from the 5U4 “cathodes” to the smoothing choke and positive of C1

4) Remove the Octal bases and fit the B9D bases in their place in the same holes trying to keep the orientation similar with regards to wiring; turn 180 degrees in this example

5) Drill a ¼” hole through the chassis between bases, de-burr and fit the ¼” grommet

6) Rewire the heaters to Pins 4&5 on each valve, and here it is necessary to maintain the pin connections ie pin 4 to pin 4 and pin 5 to pin 5.

7) Wire the Transformer HT (black) wires to pin 8 only, one wire to each valve, do not use any other pin than pin 8.

8) Connect short leads 6”/150mm or so, preferably PTFE insulated wire, to both top caps, pass them through the grommet from the top and connect both to either pin 4 or 5 of one of the 6D22S heater pins, obviously trim length to suit, but not over-tight.

9) Reconnect the feed from HT smoothing choke and CI capacitor to either pin 4 or 5 of the other 6D22S heater

10) With all valves removed plug in power and turn on. Immediately check the heater supply to the 6D22S heaters. It should be about 6 Volts ac

11) If all OK then power down and refit all the valves including the 6D22S not forgetting the top caps

12) Power up and check the 6D22S heaters which should be approx. 5 to 6V AC. Check for 425V AC between each anode (pin 8) and star earth on the PS tagboard/white transformer wire. Check for approx. 475V DC on the cathodes (top caps) with a warm-up time of about 30 secs for the HT to come up to nominal.

Please ask if not sure and feel free to add comments that may help others