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kestrelmusic · 21st Aug 2019, 9:06 pm

My next-but-one project is a Marconiphone 296 table-top set from (I think) 1934. It was given to me by a friend who bought it for a modest sum in order to extract the PX4 output valve. It has one of the nicest Art Deco cases I have seen in a long time!

Anyway, I don't propose to spend well over £100 for a replacement valve - if I change the socket for a 5 pin one I can use a ML4. The output will be reduced, but I guess it will work, and a PX4 will still fit if one becomes available.

This set used the speaker field coil, connected between the HT centre tap and the chassis earth to provide grid bias, so I can connect the ML4 cathode to earth.

However, the problem is, I suspect, going to come with the capacitors. Most of them are potted in bitumen in a metal box, which means that if more than one or two caps are duff it will be easier to replace the lot. I can presumably melt out the old bitumen and build up a new block with modern components, but can anyone suggest a suitable filling material? Ideally it wants to be liquid enough to be poured, but set reasonably firmly.

21st Aug 2019, 9:06 pm	#1
kestrelmusic Hexode Join Date: Feb 2008 Location: Wrexham, North Wales, UK. Posts: 466	Marconiphone 196 My next-but-one project is a Marconiphone 296 table-top set from (I think) 1934. It was given to me by a friend who bought it for a modest sum in order to extract the PX4 output valve. It has one of the nicest Art Deco cases I have seen in a long time! Anyway, I don't propose to spend well over £100 for a replacement valve - if I change the socket for a 5 pin one I can use a ML4. The output will be reduced, but I guess it will work, and a PX4 will still fit if one becomes available. This set used the speaker field coil, connected between the HT centre tap and the chassis earth to provide grid bias, so I can connect the ML4 cathode to earth. However, the problem is, I suspect, going to come with the capacitors. Most of them are potted in bitumen in a metal box, which means that if more than one or two caps are duff it will be easier to replace the lot. I can presumably melt out the old bitumen and build up a new block with modern components, but can anyone suggest a suitable filling material? Ideally it wants to be liquid enough to be poured, but set reasonably firmly.