Metal rectifier replacement help please

[lloydwells]

I have a battery mains portable I've posted a photo of the relevant piece of schematic I need to replace both metal rectifiers not something I'm used to doing so a bit of help with what to use please. The set uses 1.5v dry battery valves.

[Herald1360]

Hmmm, it'll need a bit of experiment to finalise, but the HT rectifier could be replaced by a UF4007 with some series resistance to bring the HT back down to its nominal value.


The LT rectifiers similarly, though there may actually be no need for extra series resistance since the low voltage likely means only a single stage MR is used with correspondingly low forward voltage drop.


I would suggest a trial run with the valves out and suitable resistors to provide the nominal HT and LT current loadings at normal HT voltage and 1.4V LT voltage with no added series resistors. Check what the actual HT and LT voltages from the PSU are with these loads and add series resistance as required to get the correct HT and LT supply voltages.

[kalee20]

What Chris says will get you started, definitely!

The final tweaks should be done with the valves in. Load resistors get very complicated to accurately replicate the valves, because some of the electrons entering the load at LT -ve don't end up at LT +ve - they take off and end up at HT +ve. So a simple resistor pair, one for LT, one for HT isn't quite right. But it's definitely the way to start!

[Herald1360]

Hmmm, wouldn't Kirchoff have an opinion on that?

Nevertheless, a final tweak "live" with valves would fine tune things. More so if the set uses 25mA rather than 50mA filaments.

Not knowing what the set is makes being specific rather than talking in general terms rather difficult.