- This topic has 1 reply, 2 voices, and was last updated 1 year, 10 months ago by Michael.
2021-March-14 at 14:57 #9126LectronFanModerator
Last year was verrry busy for me (many house improvements) so there was little time for Lectron.
And since the passing of Guenther Stabe, there is little interaction.
To honour him for his passion for radio circuits, I publish here a mail where he describes how to correctly tune a AM radio.
These are his exact words and I only quote here :
Guenther,Thank you so much for the alignment procedure.
I have added a few words – here is the actual version – hope that helps…
When all activities had no success – go to RESTART => [A]
[A] turn carefully the padding trim-Cs to 90ø (half in / half out) – double var-cap / tuning block. This can be done with a small metal screwdriver, because the cap-parts are connected to GROUND.
[B] move carefully the ferrit antenna coil to the next end with ~ 5 mm distance from the edge and tune with a modulator at 531 kHz and a signal (sine, music etc.) via variable caps (low frequency end, ~ 1 mm from the end to get the full reception) and try to get – via slowly moving the FA coil to the middle direction of the ferrite – the best reception, there must be a maximum within the first centimeters!
If not, we might have a problem…
[C] If successful, turn the osc.coil (red) slowly to the maximum loudness of the “station” 531 kHz (if in doubt first turn up and then down – no violence!).
Then the oscillator frequency is 986 kHz. Try to test via slowly turning the var.cap block, if there is only ONE station and not a “shadowed” station (then the two L/C circuits are NOT synchronous!)
[D] if o.k. so far, adjust the IF filters with 455 kHz and a 1 kHz sine wave signal injected at collector of transistor 1 – if possible -, beginning with the demodulator (1), followed by IF 2 (2) and IF1 (3, can be critical with oscillation…) ONLY in this direction – from right to left!
[E] if o.k., tune to a 1003 kHz station (AM modulator) and repeat the [D] procedure for a maximum and best sound (of the sine / music / etc.). Attention: there may be heard the two side-curves (drawing), that’s o.k., try to get the middle…
[F] If still o.k., tune to a 1456 kHz station (AM modulator) and slowly and carefully find a maximum with the Apadding trim-C. Be very careful to change the O padding trim-C for another maximum – in this case the procedure steps [B] to [F] MUST be repeated once again!!!
Anyway: I recommend to repeat the steps [B] to [F] one or more times to get the real maximum / the best possible results!
[G] Repeat the steps in the evening with stations on e.g. 540 kHz (Hungarian station) with the FA / Osc coils, around 1000 kHz with optimum sound via IF filters (from 1 to 3 !), and around 1400 kHz with the A padder/trim-c – now the superhet is fit for use!
[H] if all is fine (and only in this case) fix the ferrite antenna coil with a little hot wax on one side.
[I] do what you like to do after a – hopefully – successful repair –
2021-March-18 at 22:03 #9130MichaelKeymaster
Thank you Frank for this wonderful tribute to Guenther by including his sage counsel on this topic.
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