A Power Supply for the T1154/R1155 (/cont)

HT (1200V) Supply & Interlock

I don’t like high voltages …

But this is really a very simple power supply. Initially I intended to use a stack of zener diodes to limit the output to 1200V, which is why there is a big metal-clad resistor at the top of the photograph, and why there is a heat-sink on the front of the chassis. Then I did the maths and realised that I couldn’t afford that many high power zeners.

Each side of the full-wave bridge rectifier is made up of three 1N4007s in series, each with a 220K resistor across it. Similarly the smoothing pack consists of five 470uF capacitors in series with 220K voltage matching resistors. That amounts to approximately 94uF, give or take the relative wild tolerances of electrolytic capacitors. I have had the transformer since the 1970s and back then it powered my 2m linear. It is actually a 500 - 0 - 500 secondary. However once rectified, that unfortunately produces over 1400V. So I have wired it so that only one half of the secondary is used and the on-load voltage is closer to 770V now … adequate for getting about 30W out of the T1154 on 80m. Ideally you should be looking for an 800V/200mA secondary. The HT dynamotor was not switched on until the System Switch was set to ‘TUNE’ and subsequent positions. This also involved an interlock via the J-Switch through Plug E on the side of the transmitter. Since the only low voltage present at that time in the transmitter is 6V, the HT start-relay is powered not from 24V but 6V. I didn’t have a 6V relay with suitable contacts, so I used a small 6V relay (RLC) to route +24V to a high power 24V relay (RLD).The beautiful high-voltage connector was obtained on eBay!