> go with the larger VDC ratings (above 250), and I've
 > heard that a cap as low as 47uf might be OK - but what about
 > going the other way higher than 100 (ie 220uf) ?
You can always go higher on capacitance, for filtering.
Realisticly, probably there's only one section of the tubular thats 
going/gone out. Replacing it with three seperate caps might be alright, but I 
wish you luck...  My R-4A didn't lend itself to that much room.
 > I plan on making a PCB mounting board for the radial caps,
 > connecting the outer leads to chassis gnd and having
 > PCB pads for the anode (+) connections (inner circle), and
 > mounting that in the same place as the OEM can.
Just make sure you know what voltages are there - and, note their polarity... 
some positive, some negative (for Bias).
 > The physical size of the new components (18x32mm)
 > [DxL] doesn't seem to present any problems.
Call me an ol' phart, but I don't know what 18mm is...
rough calculations show that 18mm is somewhere around 6 inches.
100mm in one Meter, right?
around 3' = 1M
50mm = 1.5' - or 1' 6"
25mm = .75' - or 9"
12.5mm = .375' 4.5"
Ok - So, 18mm is roughly 6 inches.... and 32mm is around 1 foot.
I simply -don't- believe you've got the room for that, inside the Drake R-4.
...73 = Best Regards            -Jeff KA5THB
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