Another thing. Since you are using a 1R5 instead of the infamous 1L6, you may have to remove pin 5 of the 1R5. Pins 1 and 5 of the 1R5 are tied together internally. Not so in the 1L6. With the connection of 1 and 5 being made by the 1R5, may be upsetting the bias on the tubes. The bias circuit is quite elaborate in a TO. I have a Zenith AM only radio that had a bad 1L6 so I used a 1R5 but had to remove pin 5 to get it to work properly. If you do remove pin 5 from a 1R5, I might suggest using a Dremel tool with a cutoff disk instead of cutter pliars as the pliars may crack the tube base.

Radiodoc
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:Hi guys I need some help on this problem.
:First I'm not that knowledgeable and pretty frustrated.
:the problem is that when I press the bcb switch part way in there is reception and when it's all the way in the signal strength drops significantly especially from 800 to 550kc.note I am using a 1r5 in place of 1l6.
:Also the sets been recapped and I gave the switch assy a good clean and sprayed with deoxit.
:I was looking at the schematic fig 16 of the military manual which shows the bcb circuit but don't know what the box symbol is as opposed to that other polygonal one.
:I don't have a 1l6 so I'm not sure if this is due to the 1r5, if it is this issue may be mute.
:Any advice?
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:many thanks JIM