[Vintage-Audio] Radio Craftsmen C550 amp questions

[Paul DeFayette]

Good evening all,

I had the the good fortune of aquiring two Radio Craftsmen C550 ultra linear
amps over the last year.  Are they the same as the Craftsmen C500 amps,
except for the addition of the 5NO03 time delay relay?  If not, what are the
differences?  Is there any difference in audio quality between the two?  I
still have to check them out and recap where required, etc.  Both of mine
came with 6L6's instead of the KT66 outputs.  Is there a noticeable
difference worth upgrading to the KT66 tubes?  Which are recommended by the
group, especially of the new production?  I thank one and all in advance for
any help you can provide.  Also, I would like to purchase a xerox copy of
the original Radio Craftsmen owner/operator manual and service manual for
these amps, if anyone has them available to copy.  Happy New Year to
everyone.

Best regards,

Paul DeFayette