[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

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

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,

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