[Boatanchors] Interminable Hum!

[AWFremmer at aol.com]

Fellow Collectors/Restorers,
 
Decided to swallow my pride and come to the experts for  help.  I have an 
Allied Knight 
R-55A with a hum problem that I've been unable to  resolve.  I think I've 
isolated the source to the preamp  tube, 6AW8.  Swapping the preamp tube with 
the amp tube does not help.  When touching the shield of the tube, before 
it gets too hot to hold, I can  diminish the hum but not eliminate it.The can 
electrolytic runs cool to the  touch even with the radio on for hours.  I 
don't own a capacitor checker  but the usual ohmmeter test on all four 
sections results in the expected  downward defection and slow upward return to a 
high value of resistance.   The hum is independent of the volume control 
setting and the receiver plays  strongly enough that the hum is simply an 
annoyance but one which I can't  stand.  All screws have been snugged up.
 
A search of the Internet came up with the following web site,  
_www.ohio.edu/people/postr/bapix/r55a.htm_ 
(http://www.ohio.edu/people/postr/bapix/r55a.htm) .   Rich, KB8TAD appears to have had the same problem but his solution, 
running a  ground wire from the preamp socket to another point on the 
chassis did not  help.
 
I also own the R-55 which does not exhibit this  problem.
 
Suggestions?  And many thanks in advance for any  help.
 
73, Alan - KB2HEI