14-11-2017, 07:35 PM
(14-11-2017, 06:05 PM)Mike76 Wrote: Presumably no harm can be done by alignment, apart from physically breaking a stuck core maybe ...
It is vital that you use the correct trimming tools to fit the cores. In the first place, they mustn't be magnetic and are usually plastic, nylon or sometimes include small amounts of non-ferrous metal.
If you have cores with hexagon holes, you must use the correct hexagonal tool - other wise the core will crack and it is a lengthy and dangerous (to the core/coil assembly) to drill it out and fit another.
Older cores sometimes have a recess which looks designed for a screwdriver - but screwdrivers are ferrous and mustn't be used! When I was in my teens I used to scrounge broken bone knitting needles from my mum and file them down but I don't think you'll find them these days!
Very small cores with a continuous slotted hole through them need a tool which is usually nylon with a long non-ferrous blade attached so the it runs through the core and applies turning pressure against all the length of the core.
Regarding your signal generator and front end alignment, your generator almost certainly produces harmonics but at an unknown level.
Harmonics are products at multiples of the design frequency so, in your case, you would need to rely on a reasonable third harmonic to produce a 90MHz signal at its maximum 30MHz setting, and so on.
However, given the plethora of FM stations found in most places these days, you should find clearly identifiable stations at both ends of the VHF band which can be used for the RF alignment - provided, of course, that the tuning scale has a range of reasonably accurate markings. Identify the stations that you want to use and make a mark for each frequency somewhere that won't be seen when the set is used normally in its cabinet. Then ignore the tuning scale and tune to these marks for accurate repetition during alignment.
