[Heathkit] rit control for the 301

[Glen Zook]

Sounds like the variable capacitor in the LMO in the SB-301 needs cleaning, re-lubrication, and a grounding strap from the rotor of the capacitor to ground.  Details at

http://k9sth.com/uploads/LMO_rebuild-1.pdf


Also, the "pinch drive" for the LMO may need adjustment.  This is accomplished by removing the main tuning knob, then slightly loosening the nut that holds the shaft and moving the shaft up or down VERY slightly.  Make sure that the pinch drive stays in contact with the dial itself.  If it comes loose, then you have to "fiddle with" the assembly, by moving it up and down and pushing in and pulling out, until the pinch drive makes contact again.

The SB-301 is definitely no harder to tune than any Drake or Collins receiver that I have ever used / worked on.  The tuning should be very smooth.  However, the TRW LMOs used in the Heath equipment do tend to have problems with the grounding of the rotor of the variable capacitor after a few decades.  The original lubrication used in the bearings from the rotor to the frame of the variable capacitor dries out and the ground connection between the rotor and the chassis gets intermittent.  The old lubrication has to be cleaned out and new lubrication put in.  Then, a flexible strap really needs to be soldered to the shaft of the rotor of the variable capacitor and then run to ground.  The flexible strap prevents future problems caused by the lubrication in the shaft bearings.  Until these changes are made, many of the LMOs used in the Heath equipment get where the tuning is rough, there is a warble when the frequency is changed, etc.

You also should really perform the procedure on the LMO in the SB-401 as well.
 
Glen, K9STH


Website:  http://k9sth.com


________________________________
 From: "yash at aol.com" <yash at aol.com>
To: heathkit at mailman.qth.net 
Sent: Monday, February 25, 2013 8:53 AM
Subject: [Heathkit] rit control for the 301
 
                           Finally got the twins up and running,401/301, the 301 had a bad T-3 if transformer,found a cheap hw-17 ,stole the t-3 and replaced it in the 301, the difference is fantastic, the 301 hears everything the drake r4a hears. the 401 required some cap changes and a few resisters along with a new set of outputs. now doing full out. My concern is with the 301 ,and that it is such a simple receiver it is very touchy to tune in ,dead on. Unlike the drake ,with its notch and band pass tune control. Has any one ever come up with a RIT control for the heath? In fact any mods for receiver improvement. maybe the same for the 401.
thanks