4-400 screen modulation

[KA4RFA]

I'm just getting back into ham and I'm new to the forum.

I'm amazed at wealth knowledge of the forum members.  I have some questions.

I'm building a 50.4 AM transmitter using pair of 4-400's.  I do not have iron to plate modulate, so I want to screen modulate instead.  Has anyone done this?

Thanks!

Jim

[KC4VWU]

I know I'll probably get beat up over this, but let me make a suggestion; Cathode modulation. It's simpler, and you'll probably not notice much of a difference in the results.
73, Phil

[KM1H]

Run it as a linear, less hassles and you will still have a respectable signal if your exciter has decent audio.

In the 60's I built up a 4-400A for mountain top contesting with a club and used it for AM, CW and SSB driving with a 10A and TX converter.

Carl
KM1H

[WQ9E]

Carl makes a good point concerning simplicity and the ability to use it for other modes is definitely a plus.  I am pretty sure one of the ARRL handbooks carried a design for one.

Rodger

[Jeff W9GY]

Built a HB pair of screen modulated 4-400's several years back.  Modulation is introuced using a hi fidelity output transformer, wired hi-Z in series with adjustible screen supply. Low Z side of transformer driven by a "stick" solid state 10W audio amplifier. A little "kink"  in the envelope, but feedback not necessary. System works great, good fidelity...of course, not efficient, but for amateur use efficiency not a big deal unless you're into 'green'.

[The Slab Bacon]

Built a HB pair of screen modulated 4-400's several years back.  Modulation is introuced using a hi fidelity output transformer, wired hi-Z in series with adjustible screen supply. Low Z side of transformer driven by a "stick" solid state 10W audio amplifier. A little "kink"  in the envelope, but feedback not necessary. System works great, good fidelity...of course, not efficient, but for amateur use efficiency not a big deal unless you're into 'green'.

Applying a little of the modulating voltage in phase to the control grid biass will get rid of the "kink" and make the modulated envelope waveform look like a plate mod rig. Been there, done that.