[Reece]

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