16-03-2012, 07:22 PM
I put together this circuit a while back, no medals for originality, I actually posted it on the other forum before I quit so thought I would post it hear, It's a basic variable HT PSU built from my bits box, I forgot to put an on/off switch in the diagram and an "on" indicator bulb, all resistors .7 watt unless otherwise stated, 16 mfd is 500v dc all other caps 630v dc, it's made with two transformers, the component values are not set in stone....adjust to suit your own requirements and transformers.
As shown it will deliver 180 volts to 270 volts at up to about 70 m/a... if drawing over 20 m/a then output regulation on an increasing load is 1.25% or lower.
All heaters really need to be isolated to prevent heater cathode breakdown as shown in diagram. The only HT transformer I had to hand was a beefy 350 volt job hence the choke input filter from the rectifier, fit fuses to suit and meters to suit if required.
This unit powers (not all at the same time) an Eddyustone 358X, National HRO and Marconi R1155A no problems. The .7 watt resistors used in mine are modern types, Welwyn I think. It would probably work a bit better with a 250 volt sec. transformer. The stabalized voltage on the 85A2 is 85 volts, however the strike voltage is 115 volts, you could substitute the stabalizer valve with zenners if required, if so adust resistor to suit, if using a different valve stabalizer be carefull with the R & C value otherwise you could end up with a powerfull relaxation oscillator! Screens of transformers are earthed to mains earth.
Lawrence.
As shown it will deliver 180 volts to 270 volts at up to about 70 m/a... if drawing over 20 m/a then output regulation on an increasing load is 1.25% or lower.
All heaters really need to be isolated to prevent heater cathode breakdown as shown in diagram. The only HT transformer I had to hand was a beefy 350 volt job hence the choke input filter from the rectifier, fit fuses to suit and meters to suit if required.
This unit powers (not all at the same time) an Eddyustone 358X, National HRO and Marconi R1155A no problems. The .7 watt resistors used in mine are modern types, Welwyn I think. It would probably work a bit better with a 250 volt sec. transformer. The stabalized voltage on the 85A2 is 85 volts, however the strike voltage is 115 volts, you could substitute the stabalizer valve with zenners if required, if so adust resistor to suit, if using a different valve stabalizer be carefull with the R & C value otherwise you could end up with a powerfull relaxation oscillator! Screens of transformers are earthed to mains earth.
Lawrence.
