Marconi 200E RF Alignment

Greetings!

I have a 1942 Marconi 200E with a RF alignemnt issue that I cannot resolve. The radio was bought thru a vendor that did the usual electrical restoration.

The alignment seems to be off by about 100kc on the dial scale. 

The skematic instructions say to adjust the OSC trim to 1700kc, and the RF trim to 1600kc. Doing this seems to align station on the high end, but mis-alignes on the low end of the scale..... I need to tune to 710 to actual hear a 800kc station. 

The opposite is also true, alignment on the low end will mis-align on the high end.... 1280kc ends up at 1400kc.

This radio has no padder the helps fine tune the low end, my RCA has this thankfully.

Is there any way to resolve this? Is it an inherantly poorly designed radio circuit or is there something else that I should be looking at?

See that attachment for the circuit skematic.

Thank you for any and all suggestions! Keep in mind that I am not an expert in any way ;-)

 

Antonio.

 

Attachments:

• Marconi 200E schematic (191 KB)

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These radios didn't have a padder on the oscillator section of the variable capacitor, because the plates on this section have a special contour that accounts for the difference between RF and LO frequencies.

I note from the schematic that the IF on this model is 462.5 kHz. If someone aligned it by mistake to the more common 455 kHz, this could account for the problem. So, that's the first thing you'll need to check.

If the IF alignment checks out, then I would complete the alignment starting at the bottom of the band. Since you can't really adjust anything to set the lowest reception frequency, you'll have to adjust the pointer so that it agrees with the frequency the set is actually tuned to.

So, pick a radio station near the bottom of the band and tune the receiver to it. Then set the dial pointer to that frequency.

Then tune to a station near the top of the band, so that the pointer is pointing to the correct frequency (even if the receiver is not on frequency). Then adjust the oscillator trimmer to get the station tuned in.

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