Tuning IFT of vintage radio receiver? HOW To?

Discussion in 'Wireless & RF Design' started by yesilovethis, Aug 29, 2016.

  1. yesilovethis

    Thread Starter New Member

    Jul 28, 2016
    Dear all,
    I have bought a very old tuner Sanyo FMT 203L. The FM band works very nice with a random length (1meter may be) antenna hooked into 300ohm antenna port in the receiver's back. But when I try to listen to MW and LE band they are so faint, with highest volume I barely hear the Long wave and medium wave channels. One of my friends told me to open up and try tuning the IFT, but I do not want to do that blindly. Could you please suggest me how to proceed step by step to fine tune the radio inside with ofcourse the tuning of the IFTs if necessary. Since I am hobbyst, I have access to several measurement instruments in hand:
    Tektronix 50 MHz scope with max vertical resolution (per div.) 500micro Volt.
    Two digital multimeters.
    One wavefunction generator (cheap chinese, but works adequitely, 2MHz max).
    Capacitance meter, (inductance meter will reach by post in few days).
    Plenty of registors,capacitors,transistors (discrete components).
    I could not find the manual of 203L but here is similar model service manual:
    Let me have your suggestion.
    Many thanks.
  2. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    I would not tweak anything until I made sure with a signal generator connected to the proper antenna input something is really wrong.

    Normally there is a separate AM (AM Ext per your manual) connector screw or terminal just for MW. Internally that's connected to winding on a ferrite MW tuning antenna/coil for that frequency range on the the receiver. Have you tried connecting a proper antenna to that?
  3. yesilovethis

    Thread Starter New Member

    Jul 28, 2016
    I connected long wire in the MW/LW antenna port that did not result in good reception. Then I followed the procedure in the Manual for FMT205L and tuned the IFT (only one IFT), antenna coil slug, Local oscillator, few trimmer caps. It is now working superb (I don't know if its like new), and I am satisfied. There is a lot of RF noise in the long wave band from household items, they cause loud hums but I can always rotate my receiver to find the null point for them :)
    absf and nsaspook like this.
  4. ian field

    Distinguished Member

    Oct 27, 2012
    You can make a very simple oscillator with a 465kHz ceramic resonator from a more recent transistor radio.

    2 things to watch: The original IF may not be anywhere near 465kHz, secondly; you need to slightly stagger tune the IFTs or you'll have a very narrow AF bandwidth.

    Loosely couple the final IFT in a pocket radio to the IF stages you need to align - you should get whatever the TR is picking up without turning the IFT slug much - if in doubt; research what the IFT frequency is supposed to be.
  5. KL7AJ

    Senior Member

    Nov 4, 2008
    But but but;.....that's CHEATING@ :)
  6. ian field

    Distinguished Member

    Oct 27, 2012
    So what do you suggest? - the TS should spend thousands kitting out a radio servicing workshop with signal generators and wobbulators and other miscellaneous test instruments to align one radio!!!

    If its a standard IF frequency, alignment can be piggybacked off a working AM set.

    Salvaged IF ceramic filters make a basic alignment oscillator childs play - modulating it isn't difficult either.

    Some of the real vintage old valve sets used weird IF frequencies - Ceramic filters from a ham radio supplier could well be close enough.