[AMRadio] Low modulation Gates BC-1T


SBJohnston at aol.com SBJohnston at aol.com
Sun Feb 25 14:43:06 EST 2007


hbco2 at sbcglobal.net writes:

> I still suspect a phasing problem, perhaps a double error.

I know what you mean, but I did use a dual-trace scope to confirm that the 
grids of the push-pull 1st audio stage are getting signals that are 180 deg out 
of phase from each other.  I will do the same on the grids of the 833s later 
today to make sure that is carried through to them.

The entire low-level audio section, from 1st audio to the grids of the 833s, 
has been replaced with another pc board, this one with 807s instead of the 
sweep tubes.  The low-modulation condition was the same with the earlier board in 
place as on the 807 version.  

While the designers were a bit silly to use printed circuitry in this rig, I 
do admit that the pc board helps ensure that no wires are swapped within the 
stages.  Every component on the 807 audio board is brand new and checked.   

>Another thought is to temporarily disable one half of the push-pull
>circuitry, perhaps by removing tubes.  If you get more output from one-half
>the circuit, it would verify a phasing problem.

Good idea - I'll give that a try.

>Wonder also if you have a large power resistor (200 w) of 2500-5000 ohms 

I wish I did, but so far I've not found anything high enough that could 
serve.  Drives me nuts to think of the multitudes of suitable resistors I've had 
broadcast sites in my past positions - no access now.  The big resistor I have 
is 50 ohm as shown in the photo at 

http://www.wd8das.net/BigR.jpg

-grin-

Steve  WD8DAS




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