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Old 21st Aug 2017, 3:21 pm   #1
Voxophone
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Default Marconi T21A Pre-set stations

Hi All,

I’m currently restoring a Marconi T21A and have a question regarding the pre-set station positions.

The LW position is working on my set (although the reception of LW is poor in my area), but the two MW positions seem to be dead. All I can hear is noise.

The Trader sheet for this model advises you to adjust the appropriate core and capacitor ‘for maximum output while receiving the desired transmission’. I’m unsure how you’re meant to find the ‘desired transmission’ to begin with as in the pre-set positions the tuning pointer is not used. To find a station using a pre-set, do you basically have to fiddle with the adjustments until you hear something?

As part of my fault finding I’ve checked every switch in the unit and all appear to operate in the correct sequence. The coils used with the adjustments measure correctly for resistance. I’m unsure what else to try.

Any suggestions?

Thanks
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Old 21st Aug 2017, 4:04 pm   #2
ms660
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Default Re: Marconi T21A Pre-set stations

Switch to a preset, connect sig gen to the antenna input, modulation on, tune sig gen to existing preset frequency and peak up the preset adjustments, adjust the sig gen a little in the direction of your chosen preset frequency, peak up preset adjustments again....repeat until you get there (to your chosen frequency) eg: adjust, shift, chase.... less chance of "getting lost" that way, when you get there do final adjustments using your chosen transmission.

Lawrence.

Last edited by ms660; 21st Aug 2017 at 4:08 pm. Reason: clarification
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Old 21st Aug 2017, 5:02 pm   #3
Voxophone
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Default Re: Marconi T21A Pre-set stations

Thanks Lawrence. I'll give that a try. The Trader sheet gives the wavelength range for each pre-set, which should narrow it down a bit.
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