— Coil cores (slugs) with hexagonal hole can be damaged easily!

The screw pitch of these coils may be very hard to be adjusted and the coil form or the ferrite core can break, also, in a frequent retouch, the ferrite thread and/or the thread inside the coil form can wear down running too loose causing variations on tuning after the radio has moved. Unnecessary fiddling can damage threads of coil cores or worn-out coil grooves.

Hammarlund slugs have an hexagonal hole that passes through its center, oftentimes what appears to be a stuck slug is actually a broken slug. Never force a slug with a tool that allows some play, you'll ruin that slug if it tends to get stuck. The tool must slide perfectly in the slug; if you try to use an hex tool that allows some rotation before engaging, it can break that slug during the adjustment travel, this will permanently seize up the broken slug into the coil. These slugs usually become splitted in two along its hexagonal hole, the hex bar tool used to adjust separates the broken halves by pressing them against the wall of the coil form: when turned harder, the halves grip the wall of the coil more tightly. That's why when a slug seems "freezed" or "sticked" never must be forced, since there is a potential risk that the whole coil will twist inside itself and tear off the wires coming off the coil to the connections base. If the slug is hard but ain't broken use a very solid and rigid hexagonal bar that fits exactly to the central hole of the slug. A broken slug should be carefully removed (destroyed) using the tip of a needle, and then replaced.

— "Excessive" modern design on Mixer-Converter & IF transformers!

In later Hammarlunds the coils are modern at the best and worst meaning of the word, that is, the form factor is designed to provide a high Q, but design criteria to avoid manual labor are also used as well as cheap material (plastic). Someone thought that the tuning capacitors were installed using built-in open construction mica insulated caps and that could be located in the plastic mounting base connected using the usual solder lugs of the coil (internal ends are moulded like a clamp), and these ends were used to make contact by surface pressure on the mica. The result is that the reliability over time of these transformers depends on how careful that was the mounting employee to avoid forcing or twisting these solder lugs and not heating them too much when welding. If this occurs, contact pressure is weakened, this creates a "variable resistor" in series with the tuning capacitor, and the results are: a permanent loss of gain, a sporadic sound like storm static, or sudden changes in volume. The solution is increase pressure if the contact surfaces are not affected, or deleting the "modernity" installing normal sealed caps.

The issue due bad pressure contact may be confused with another issue: The Hammarlund popular "Silver Mica Disease".