[AMRadio] Johnson Valiant Modulator Plate Lead Question


w0ng at comcast.net w0ng at comcast.net
Sun Aug 12 14:12:07 EDT 2007


Grant,

Thanks for the advice. It's appreciated.

73
Bill
w0ng
-------------- Original message -------------- 
From: "Grant Youngman" <nq5t at tx.rr.com> 

> > Is there any truth (or significant value in performance) to 
> > this concept that it does matter which plate lead connects to 
> > each modulator tube? Appreciate any advice the list 
> > membership might have. Bill, w0ng. 
> 
> Yes. 
> 
> The male voice waveform tends to be very asymmetrical. If the phase is 
> incorrect the radio will likely hit 100% negative modulation before getting 
> to 100% positive. 
> 
> There is more than one way to skin the cat. You can (1) just reverse the 
> mic leads -- thus reversing the phase. Or you can (2) swap the phase by 
> changing plate leads on the modulator (or by swapping the leads on the 
> driver transformer, etc.). Or you can use an all pass filter in the audio 
> chain which will remove the asymmetry altogether. 
> 
> In any case, the objective (and you should have a scope to check which is 
> which) is to get highest possible positive peaks before you hit 100% on the 
> negative peaks. 
> 
> Grant/NQ5T 
> 
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