How Much Negative Feedback Do You Use

[W2JBL]

   back when i had a Ranger i stuffed a Viking-II mod transformer in it. it fit Ok, then a pair of 807's and 12BH7 phase inverter in it. i used the 500 ohm tap on the mod transformer secndary to provide a feedback loop to the second audio stage. sounded great and had tons of audio. more recently in the ARC-5 project i used the same phase inverter and 807's but with a ART-13
mod transformer. I used the screen winding on the secondary for the loop and again back to the cathode resistor of the second half of the 12AX7 speech amp. it's about 10DB of feedback. works real slick, and i get very clean audio out of it. next thing i am going to try is feedback aorund the modulator in my ART-13. i did not beleive in using negative feedback for years but last winter after i tried it in my Viking-II i was impressed by what it could do.

[k4kyv]

I had the oscillation problem with a Ranger when I took out the high frequency rolloff capacitors, so I simply disconnected the feedback loop.

The reason the Ranger has negative feedback is because it was designed to also work as an exciter for the Desk KW.  For exciter service, the modulator is designed to drive the 810 class-B modulators.

Beam power tubes make very poor class-B drivers unless you use negative feedback, which lowers the effective plate resistance of the tubes.

So if you don't plan to use the Ranger audio to drive a high power class AB2 or class B modulator, there is no need for the negative feedback.

I don't use any negative feedback in my homebrew transmitters, but my Gates BC1-T uses a feedback loop between the plates of the modulator tubes and the first 807 audio stage.

[ka3zlr]

If I may,

 Meaning No Disrespect,on the 100 watt or less class... I think it's much more efficient to stabilize the transmitter itself first, treat it as exactly that .. then go entirely outboard with the reverse audio transformer approach and do all the vocal trimming in the audio rack. it's so much easier, everything is within reach then...and there are some great choices for iron..