Marconi model 557

[1100 man]

Originally Posted by turretslug

The MU14 and IW4/ are indirectly-heated, these types generally seem to have a lower forward drop than directly-heated types, perhaps due to the more consistent spacing of anode/cathode possible over a wider area, or simply having a bigger cathode surface.

That's interesting. I was rather surprised to get a much higher voltage with the indirectly heated types.
The IW4/500 gave 395V across the reservoir capacitor
The rectifier I have settled on, mainly because it gave almost the correct HT, was in a box marked IW4/350 and then in pencil R2, R42. It is clearly none of these as it's obvious that the electrode structure does not incorporate a cathode.
Looking at the 'r type' site, it looks like a DW4 directly heated type.

Hopefully, some axial electrolytics will turn up from RS tomorrow, so I can tidy up the components just tacked in to make it work. I can then continue to fault find the RF stage.
All the best
Nick