A little distraction

I've not made any progress with the R1155L since it appeared on my workbench earlier this month. It's still there, it just got pushed to one side. I've not been idle though, over the last couple of weeks I've been building the power supply and audio amplifier that I will eventually be needed to run the receiver. I could have built one with modern components, but I decided that a valve (tube) design would be more appropriate.

Front view. The hole is for a neon 'HT on' indicator.

The power supply is built onto a simple folded aluminium chassis purchased from a seller on eBay, and in the best tradition of radio recycling, most of the parts are recovered from other radios and electronic equipment. After the chassis the most expensive item was the 5Z4G rectifier valve, although the KT63 tetrode could have been quite costly if I didn't have one already.

Rear view of KT63 (left) and 5Z4G (right)

The transformer was the most difficult item to source. With multiple windings to provide HT, rectifier heater and LT supplies, this style of transformer probably hasn't been manufactured since the 1960s when silicon diodes began to replace valve rectifiers. An R1155 (especially one with the DF valves refitted) will require more heater current than most domestic radio transformers could provide, so I had to limit my search to old industrial and military equipment. Fortunately last year's visit to the National Vintage Communications Fair in Warwick proved to be very worthwhile, and I came home with both a suitable transformer and a choke to go with it.

Underside view. All wire is silicone insulated, except for AC cable.

The connection to the power supply are brought out to a tagstrip on the rear of the chassis. HT- and chassis are on separate terminals, and the LT supply is also isolated from the chassis. This will allow me to add wire links as required for use with either my R1155 (floating HT & grounded LT) or my HRO receiver (grounded HT & floating LT).

The PSU is now working, but for safety's sake it needs to be finished with some form of case. There are dangerous voltages on the transformer terminals just behind the rectifier valve, and also below the chassis.

Building it has been an enjoyable distraction, and its actually the first bit of valve equipment that I have ever built from scratch. Now I need to face the more difficult task...the R1155 itself.

Keep listening!