[Hammarlund] new tubes and SP-600 noise floor

[Craig Roberts]

Calling all SP-600 jocks --

Just for fun, I'm incrementally re-tubing my SP-600 with NOS JAN tubes. U=
npleasant experiences and long nights have taught me to approach this sor=
t of thing one-tube-at-a-time (if at all).

While working on the IF string of 6BA6s, I noted that the internal noise =
floor of the receiver was raised considerably by the installation of a 57=
49W (a 6BA6 military equivalent) at the IF driver position V11. Re-insert=
ion of the original Sylvania 6BA6/EF94 JAN tube brought the noise level b=
ack down. In fact, the Sylvania tube was a bit quieter in this socket tha=
n the old RCA 6BA6s used originally at other points in the receiver.

Has anyone else noted a particular noise sensitivity at V11?  For that ma=
tter, how much noise do you experience with the mode switch in the "Send"=
 position and the RF Gain fully clockwise, and, like mine, does your inte=
rnal noise increase at the 8 KC selectivity position?

My receiver was especially =93crackly=94 when I got it, but the scrubbing=
 out of every tube socket pin in the set with DeOxit and interdental brus=
hes toned it down considerably. =


Thanks and 73,
Craig
W3CRR