SB-300 Receiver problem

[John Campbell]

Mark and All:
      This problem is most likely caused by dried out lubricant in the LMO
tuning capacitor. The cure is to disassemble to LMO enough to expose the
tuning capacitor, then carefully remove whatever old lubricant you can with
a degreaser and a small solder flux-brush. After drying, use a small amount
of lubricant on each of the capacitor rotor shaft bearings. Lubricants like
lubri-plate or even clear silicone grease have proven effective for me.
There is also a silicone grease which contains graphite (don't know the
brand name) which is "conductive". This is the ideal stuff because it would
help keep the rotor at ground potential and prevent the frequency jumping
you are describing.
                      73....John   <<w8jnc>>


>From: "Mark V. Johnson VE3DJU" <mjohnson at CA.IBM.COM>
>Reply-To: mjohnson at CA.IBM.COM
>To: HEATH at LISTSERV.TEMPE.GOV
>Subject: SB-300 Receiver problem
>Date: Sun, 13 Feb 2000 10:43:59 -0500
>
>Hello All...Once again I'm turning to the collective wisdom of the team to
>offer an ideas regarding a problem I'm having on my SB-300 receiver.
>
>The rig is in fairly good shape...well built...no mods of any consequence.
>The problem..when tuning on some CW, RTTY or even the odd SSB signal, the
>signal sounds distorted/unstable or jumpy, when tuning it in..Almost like
>an unstable BFO on a cheap receiver. When you stop tuning (turning the tune
>knob) the instability settles immediately. When you turn the knob to get
>the right pitch on a CW signal, it gets jittery again.  It happens in the
>USB and LSB mode, it is not dependent on the AGC setting, cutting back on
>the RF gain does not effect it, and it only seems to happen on some
>signals. Not all!! Not a big problem, but something's not right and it s
>gonna drive me nuts until I find it. Unless someone can tell me its an
>inherent design issue, which I doubt.
>
>Someone has been into the LMO as it is a 6CB6 tube( I believe a 6AU6 was
>std) and the screws are no longer sealed. . I put my scope on the LMO
>output and it appears very clean and stable. As I tune it, it changes freq
>very nicely..no apparent distortion.
>
>The problem occurs with the receiver in standalone mode and when mated to
>my  SB-400.
>
>Any ideas are welcome and appreciated!! TNX
>
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