[AMRadio] B&W 5100B Modulation Update


Geoff/W5OMR w5omr at w5omr.shacknet.nu
Wed Oct 13 15:02:54 EDT 2004


> Yes there is a plate current position and it shows a definite rise in
> current with modulation. There are dual 5U4's in the supply feeding the
> finals and modulator and I swapped them both out with the same results. I am
> leaning towards Gary suggestion that there is an impedance mismatch causing
> excessive current draw. Does anyone have a 5100B or know what the impedance
> of the primary and secondary should be. I will try another set of caps this
> evening when I get home there are 2 , 40uf in series on the B+ line.

finding out what the final Z is, is as simple as using ohms law (close enough
in this case) where R(or Z, if you prefer) of the final is equal to Voltage over
Current.
R=Ep/Ip.

so, given that the Ep is 600VDC, and I'm guessing that Ip would be around 225mA

R=600/0.225
R= (around) 2.7kOhms.  Kinda low, actually.

You'd need a modulater Z of around 2k.

Sounds kinda like a 1:1.4 turns ratio is what's needed.

73 = Best Regards,
-Geoff/W5OMR





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