Re: 160 /80 / 60 mtr AM TX project
Hi Ian and others,
This project was conceived initially as a Codar AT5 copy but grew / evolved into this.
I always plan things out with cardboard cut outs first - can't be bothered with a full 3D CAD package, but seems to work out ok.
Just been doing some tests on the modulator and I think I have a problem in either the output valves or transformer as I can't achieve more than about 70% modulation before clipping sets in.
I notice the DC resistance on the UM2 transformer primaries are different, one side measures 71 ohms (pins 3 to 5) and the other side measures 92 ohms (pins 4 - 2). This might be just down to the way it's wound as under AC conditions the ratios seem the same.
Full winding 3 to 6 measures 114 ohm while the other side 4 to 1 measures 155 ohms .
None the less when running for real the 3 - 5 side (lower resistance side) seems to create a distorted sine wave on the anode whereas the other side seems ok.
Hope its not shorted turns !
Bias is balanced as is the drive signal.
I'll try switch valves over and / or different taps to see what happens - hope its nothing serious !
I wonder what the DC resistances should be for UM2 ? I've not been able to find them on line so far.
Any suggestions ?
Regards Tim
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Building and tinkering for over 50 years, from 807's to digital amateur TV.
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