[AMRadio] AM and power

[rbethman]

The BC-610/T-213 uses 100THs for modulating the 250TH.  In both cases 
they are Triodes.

I'll add that the 100THs don't do squat for throttling the modulation. 
The system requires that very close attention must be paid to the 
Microphone gain.  The Audio limiter circuitry is NOT a compressor.

It will act as a clipper.  Properly setting it with an injected sine 
wave audio generator, and adjusting as specified in the TM will "start" 
to help the situation.

The carbon mic isn't wort connecting.  The ER Articles showed that the 
best modulation percentage achieved was about 40%.

The Dynamic Mic input, with a "suitable" microphone provides 
significantly better results.  I use a Shure 737A.

As is true for ANY tube based transmitter, the "Throttling" agent is the 
Operator!

Additionally, while everyone goes ballistic over re-capping receivers, 
the BC-614s require the same treatment.

There were two articles in ER, by Bill Feldmann, N6PY, (Issues #185 & # 
186.), showing the issue very clearly.

Many of the audio stages in the BC-614 series of Speech Amplifiers have 
the OLD "Mica-Mold" paper capacitors that proved to be inordinately 
leaky.  He pointed out that these were noted during WWII as showing up 
as an issue.

So 60+ years later, it is no surprise that they require attention

Bob - N0DGN