DC battery eliminator a bit of help please.

[lloydwells]

Ok I have a couple of 1920s American battery sets I've never used them as they need just about every voltage going so I thought I'd got lucky when I found an eliminator for a tenner ! One problem turns out it's DC �� so I'd like a way to turn some AC in to some DC to run this thing. It's HT only so shouldn't draw much current at all and I'm fine for an LT supply I have that just need to rectify mains and smooth it enough to work and be able to fit the bits to do it inside this things box.

[ekjdm14]

Depends what the voltage input is, looks like 220VDC in the photo? Wouldn't expect it to draw that much current being an HT supply

I'm thinking either 4 1N4007's bridged or one of the bridge rectifier chips commonly found in random power adaptors, suitable sized dropper resistor to tame it down a bit & a couple of 10uF/350V caps ought to do.

Or maybe just a couple of diodes rather than the full bridge, if that made things a bit too "hot" on the voltage.

[Silicon]

Does the radio use directly heated valves? I expect it does.

If I understand you correctly you have an 'Eliminator' which turns 230V DC into the various DC voltages needed for vintage radios.

If you do build a AC to DC power supply I recommend you incorporate some low value fuses and/or low voltage low current series wired bulbs to limit the current under fault conditions.

Replacement valves may be expensive.

[lloydwells]

Yes it's on directly heated valves and yes it takes in 230v DC obviously id fuse it this thing is 90 years old and in a wooden box I don't really want it spontaneously combusting I got brave and linked in a bridge rectifier pinched of a beko washing machine motor board with a 50uf 450v electrolytic across the rectifiers output and the thing works !! Our mains seems to come out of the wall at 245v the eliminator was spitting out near enough what it should all the voltages were between 3 and 5 volts high but obviously there was no load on it.
It's mainly the smoothing things side of it I need help with.

[Herald1360]

You are using an isolation transformer to feed the bridge, I hope! If not the whole shebang will be live at some indeterminate voltage around half mains! Not recommended for battery sets with earth connections nor survival of the user!

[lloydwells]

Thank you the ministry of the obvious I'm not plugging a wooden box full of 90 year old components and tar directly in to the mains I like my house.

[Herald1360]

Fair enough, but the fire risk will be much the same, transformer or no.

[paulsherwin]

Let's keep it friendly please.

[Herald1360]

Originally Posted by lloydwells

Yes it's on directly heated valves and yes it takes in 230v DC obviously id fuse it this thing is 90 years old and in a wooden box I don't really want it spontaneously combusting I got brave and linked in a bridge rectifier pinched of a beko washing machine motor board with a 50uf 450v electrolytic across the rectifiers output and the thing works !! Our mains seems to come out of the wall at 245v the eliminator was spitting out near enough what it should all the voltages were between 3 and 5 volts high but obviously there was no load on it.
It's mainly the smoothing things side of it I need help with.

OK..... for some really meaningful suggestions about improving its smoothing performance to cope with ripply dc from rectified 240V ac, a reverse engineered circuit for what is already in the box plus information on what current loadings will be applied to the various outputs will be needed.

Off the cuff I would say that if it's designed for 230V dc input, then you will need about 180V ac from a transformer feeding a bridge then a 100uF or so reservoir cap followed by 100R and another 100uF smoothing. See circuit attached.

This will deliver around 230V pretty smooth dc with a 50mA load. Actual voltages from the eleiminator will depend on what's in what I suspect will be a resistive potential divider chain and what loads you put on its outputs.