The AM Forum

Probably old hat to some.

How commercial people did it back in the day..........

Page 71.

http://www.americanradiohistory.com/Archive-Radio-Electronics/50s/1951/Radio-Electronics-1951-03.pdf

The article that peaked my interest was the Drive-In movie theater article.

One of my first "EElectrical" jobs ever was replacing speakers and speaker cables and checking wiring back to the amp, replacing bad tubes, etc.

And oh yea, occasionally dressing up as a monster to scare the patrons when those Horror Movies were on the screen. We got paid for that too. ;)

Phil - AC0OB

Same here - the outdoor theatre piece triggered old memories.  In the early 50s there was one of them 100 yds or so from the family home.  I got a job washing windows to incoming patrons for which I got paid NOTHING - tips only...and those were few and far between.  However, there was a side benefit.  I got chummy with the projectionist who gave me all the 6L6 pulls from the audio amps (and there were a lot of them..guess the amp design left something to be desired).  Anyway, those soft 6L6s wound up in early AM transmitters one of which was on the broadcast band.  At 16 yrs of age I was playing 45 RPM requests to my buds and their girlfriends around town (I didn't have any girlfriends of my own - too skinny and pimply).. ;D

Rod KQ6F

To get back on topic, that method of optimizing neutralization seems to have been pretty obscure in past descriptions of the process, at least to me. Others on here might be familiar with it but I don't recall reading about it previously, even in prewar QSTs. It's certainly worth knowing and also highlights the obscure but useful trove of information buried in Radio Electronics and predecessor publications of Hugo Gernsback. Thanks for bringing that useful tip to our attention!

Bob - NE

Off topic, but that's my friend Bob Gunderson-W2JIO (sk) on the cover!  He and his wife Linda use to drive down to our QTH and camp out in their motor home in our back yard.  Many enjoyable hour spent with this brilliant man.  Blind since birth, but that never slowed him down.  We were collaborating on some test equipment which would have served the blind community and then he suddenly passed away. 

Joe-GMS       

I was aware of that method of neutralizing an RF amplifier but I never did it that way.  I never heard it called "Dynamic Neutralization, although I can see how they came up with that term. 

My mentor taught me to apply RF drive, remove the plate voltage on the tube while observing the feed-through power measured with a scope across a 50 ohm dummy load on the output.  Then one would alternately tune the grid and tank capacitor until a peak was observed.  The peak was then minimized by tuning the neutralizing capacitor for a null.  It took several times of going back and forth with the grid and tank tuning finding a peak and then nulling with the neutralizing capacitor.  Also, it should be done on the highest frequency band.  It worked well and never had an issue using that method. 

Joe - GMS   

In general, Neutralization can be viewed as a balanced Capacitance Bridge situation such that

Cn = C*(Cgp/Cgf)

where Cn = neutralization capacitance,
C = input circuit by-pass capacitor,
Cgp is the grid-to-plate capacitance,
Cgf is the total input capacitance including tube and stray capacitance.


Jerry Whitaker and Frederich Terman use similar equations.

This article in my view is more about practical neutralization than any "dynamic" facets.

The author doesn't mention that the 10m band is one to start with since it is usually that band where parasitics are most likely to be found.


Phil - AC0OB

Analyzing neutralization as a bridge is an excellent way to consider it. Bob Dennison, W2HBE (SK) employed that concept in a low power 40/20 meter amplifier he designed and described in October 1953 QST. It used a 6AQ5 driver and 815 dual beam-tetrode final operating as a push-push doubler on 20 and straight-through amplifier on 40. As a doubler the 815 did not require neutralization and when operated straight-through, the heater of one section was turned off, so its grid-plate and circuit capacitances perfectly neutralized the active single-ended amp! The concept did not originate with Bob, but it was utilized in a clever way.

Bob - NE