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Old 11th Nov 2012, 2:12 pm   #1
Mans Veldman
Retired Dormant Member
 
Join Date: Dec 2010
Location: Leidschendam (near The Hague), The Netherlands
Posts: 16
Default R1556A High imp. phones

I finished restoring my R1556a (AR-88) receiver. It has got a full mechanical and electrical restoration including a recap of the leaky bathtubs.

After a re-alignment it plays again as it should. Besides the low imp. phone connection the R1556A also has a high-impedance phones connection at the front and although the white plastic plate looks a bit amateuristic it is original. I did see this kind of white plastic indicationplate on several original war-time photo's.

The high-Z connection is established by connecting it, through a capacitor, to the primary side of the output transformer. This capacitor (paper/wax) also proves the originality of the high-Z connection because it has been stamped aug. 1944. This is the only recognizable stamp. I cannot read it's value anymore. It looks something like 0.x7 uF but could easily be something else. Measured on my C-meter it says 113nF but that is of not much value because it already shows several mA leakcurrent at 150V.

I want to replace it but could'nt find anything about it in RCA manuals or British EMER's. My guess is that it's a 470nF/500V C, but I am not sure. I guess anything between 100nF and 1uF will do, but I like to know the original value. Does someone now the exact value, or has documentation about the R1556A specifically?

I attached some photo's. The bathtubs where leaking oil and the rubber seals deteriorated. I completely gutted the bathtubes including the seals en solderlugs (taking precautions in dealing with the PCB containing oil/residue). After that I restored them using Philips capacity less feedthroughs. Although not original anymore it looks very acceptable to me.

'73 Mans - PA2HGJ
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