[AMRadio] Low modulation Gates BC-1T

SBJohnston at aol.com SBJohnston at aol.com
Mon Feb 26 23:39:57 EST 2007

Jim wrote:

>Steve, I'm sure your getting  frustrated.  Hang in there  
>since the solution is close now. When it is all over and 
>we all look back on it, it needs to make sense.  

That's one reason I'm going over it on the mailing list - I'm sure it has 
educational value to a number of folks.  And I needed suggestions!  -grin-   I 
really appreciate everyone's kind assistance...

>I brought up the need for a AC compensated 1000x HV 
>scope probe early in this thread. Nobody until John has mentioned this 

After your earlier suggestion I shopped for one but the cost was too much for 
me to justify at this time.  It is an excellent idea, and thank you very much 
for the offer to loan me one.

>Are the tubes sharing the load?  

Yes, I'd say so.  The plates color equally and the individual currents are 
nearly the same... 100 ma each for the 200 ma combined for example.

>You said that you got 200V X 5 across those resistors (RMS). 
>What kind of meter do you use?

In that case I was using my Fluke 70-something:  RMS reading with flat AC 
response in the audio range.   

>If the modulation transformer is shot, expect to see the  
>audio waveform distort badly as you bring up the drive. 
>In fact, the distortion may be mainly on one tube (every 
>other pulse of Class B modulator current).

Interesting you should mention that.  Yesterday during another test I zoomed 
in on the wimpy waveform of the audio on the RF envelope, and noticed that it 
was smooth on the positive peak, but had a discontinuity on the negative-going 
"peaks" (dips).


Steve WD8DAS

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