Bias Supply transformer

[W7SOE]

K1JJ's 813 design calls for a 100VAC transformer to be used for the fixed bias supply.

Any reason that I can't use a small (100VA) isolation transformer?

Thanks

Rich

[W2PFY]

None at all. All you need is the voltage and the current. some people might have a 10 volt transformer that could be backwards hooked to the 813 10 volt source and then take the secondary 115 volts and  rectifier it to run to the VR tube. The resistor might need to larger in value to get the VR in the proper operating voltage.

I see JJ's power supply is at 110 volts but I have seldom seen a voltage that low in the last thirty years. In any event, the 1 K adjustable resistor would be the main adjustment for the bias in this scheme.

[W7SOE]

Thanks for that, I was just making sure that I was not missing something.

Rich

[k4kyv]

A small isolation transformer, something you could use to pull 110v at 1/2 to 1 amp.  Solid state bridge rectifier made of four 600v 1 amp diodes.  A 1000 mfd or so, 250 wvdc electrolytic. A 250-ohm wirewound rheostat.  No VR tube necessary.

A reverse wired filament transformer would work FB OM.