Floating Freq.
 

I have a Zenith 10s153 that has two slight issues. The first is freq. shift.One day 1220 am. is at that spot on the dial and the next it will be at about 1270 on the dial. There are a few stations I listen to that are at 1150 and higher that all do the same thing. But a week later it will be where it should. I replaced all paper caps and filters, calibrated it up per diagram.So, why do the stations float? This only happens at start up. If I run the radio for hours the stations will stay where they were on start up.Also the 600kc. trimmer is bad When I order a new one what pf. range should I get? Thanks, Doug

Sounds like the oscillator section is jumping around due to changes in component values. May just be dirty contacts.

Wiggle the oscillator tube in its socket, 6A8: get static or station jumping around or cutting out? Clean all tube pins and sockets. Use CRC Electronic Cleaner, available at auto parts stores. Use sparingly, don't soak. Rub around inside tube socket contacts with pipe cleaner or toothpick. Wet tube pins and plug tubes in and out of sockets while wet with cleaner. Also clean the grid caps and clips. All grid caps still glued tight on top of tubes? Check all solder joints in the oscillator section for a cold joint.

Use same on bandswitch contacts, don't soak switch wafers. Just on the contacts, while working switch back and forth. Check all solder joints on switch.

Try another 6A8 tube if you have one.

Check all component values in the oscillator section.

Are you sure the 600kc cap is bad? Should be able to repair it. Often you can take apart a noisy cap: take note of how many turns to remove the screw so you can get it back together close to the adjustment where it was. Take careful note of where all the washers, mica insulators, etc. go. Clean all pieces both sides with cotton swabs and alcohol. Reassemble. If somebody took it apart before, they may have left out an insulator or two, or the insulating washer that goes under the screw head. Improvise. You can use a piece of thin plastic, or the mica used on power transistor mounts. The washer can be fiber, or you can find nylon ones at Lowe's or Home Despot (what my bro in law calls it, jokingly) in the miscellaneous parts.

Good luck and let us know if any of this did anything.

Reece

The radio will not even pick up static below 700kc. I did use Deox-it on all connections but I will check what you said, Lord knows that this wouldn't be the first time I missed something, Thanks!

Might be a bent tuning cap plate that shorts out when you tune below 700KHz. The problem spot would be just entering the mesh when you tune just at 700KHz. Higher frequencies it would be outside the meshed area of the cap. If it's the local oscillator cap, the radio would go completely quiet if the oscillator goes dead. But so would the radio if it was the antenna circuit.

WA2ISE has a good idea about the tuning cap perhaps shorting out. Sometimes this is hard to see. To test, unsolder the wires to the stators of the cap. Clip your ohmmeter between one stator and cap frame. Turn cap through its range. Then do same with other stator. Should have infinite ohms throughout. Also clean spring contact between cap frame and rotor shaft (this cap may use another method of insuring electrical continuity to the rotor?)

Reece

This may sound silly but just to be sure...Are the Tuning Capacitor blades straight and parallel to each other?
The reason I bring this up is that I have an Emerson AC-149 that had been messed up by some hacker before me and the oscillator would drop out. Sure enough, the outermost blade was bent outwards to affect it. I "carefully" straightned it parallel with the others and problem solved.
So, even though there were no "shorts" the spacing was affecting proper operation!

Bending the outer blade is a proper technique for adjusting the tracking for many radios. It sounds like it may not have been done properly on your Emerson by the previous person.

John