Nordic Breeds WA4VZQ wrote:
Read Lynn's post again. He said the carrier was strong but the audio was
quite weak. It is quite difficult to get over 95% modulation with a
suppressor modulator. With beam power tubes, you get far less than this.
Also you get lots of distortion because the beam forming plates do not
linearly control plate current, so you have to lower the modulation level
even further to make the audio readable by listeners. Hence the "strong
signal with very low modulation level" makes sense.

My experience was about 25% modulation, and that was with distortion that
was... well... kind of bad.

I would characterize this as pretty much the worst quality AM ever, worse
than screen grid modulation by a long shot.

Fortunately with
pentodes, it is easy to drive the output to zero (negative modulation).
The real problem occurs when the suppressor is driven very far into the
positive voltage region and it starts drawing current. Typically the
suppressor grid can only dissipate a few watts. Since current is drawn
during the positive peaks, an audio driver must present a low impedance.

And this also quickly becomes a distortion source unless the audio driver
stage is pretty hefty.

Just say no.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."