[QUOTE=Haz-Mat-Strat;7409287]The 2.2uf Epcos cap looks like it is the last stage of filtering/ decoupling on the B+ voltage and the 160v capacitor is the transformer coupling capacitor. Both of these capacitors are MKT / polyester capacitors. They are the same as the Seimans.
The 100uf looks like it is the cathode bypass and it has a small film bypass capacitor to add back some highs into the mic.
The tube is the Russian 6c31b-p and was used in the early Lomo 19a19 mic.
The ceramic cap (C5) should be replaced with a Polystyrene, Silver Mica, or polypropylene.
I thought that ceramic cap looked like a bit of a weak link. Would you recommend replacing it with something of the same value?
It say 102 2kv on it. I guess that's 1000pico farad. I have had trouble finding a 2kv Mica cap anywhere.
How about this sort of thing? http://uk.farnell.com/evox-rifa/phe4...mmp/dp/1678922
This looks interesting too but 2000pF. http://www.ebay.co.uk/itm/DUBILIER-M...item1c226852fc
It looks as though the rest of the circuit is pretty decent though.
A better transformer would probably help.
I have been researching the LOMO19a19 with a view to converting the OM7 to as close as possible to a replica but i haven't been able to find any info on the transformer yet. I know it used a CK12 edge terminated capsule. The lundahl 1587 could be a possibility. Obviously the headbasket on th 19a19 was quite different to any other tube mic i've come across but they do sound lovely. I found this circuit which could be a good starting point.
An OM19 perhaps!?