|[AMRadio] Ranger... good news, bad news|
gblau at w3am.com
Sat Nov 4 20:50:04 EST 2006
Yes, the screen mod can be made on its own, as can most of the others.
Although it will change the Z the modulator works into it will not have
a dramatic effect on audio performance which, quite frankly, already
isn't too hot with the stock audio stages and mod xfmr. (Hence the more
involved audio mods.)
I certainly would not lump a screen adjust mod into the same power
reducing option basket as a T connection and a dummy load or reducing
loading, both of which I would agree are bad (lazy) ideas.
The compromise in adjusting the screen is a small one.
Try it and see, if you don't like it it's simple enough to take it out.
FWIW it worked great for me.
If all you want is to reduce the RF to feed a linear then just do the
screen mod, or something like it. Many ways to skin this cat. All
depends how complex you want to make things.
Jack Schmidling wrote:
> Guess I missed that "detail". Question though... can that change be made
> on it's own?
> Secondly, I found this contrary statement on another site....
> Most often mis-modification:
> Reducing output power when driving a linear amplifier through the use of
> a T connection and a dummy load and/or reducing loading or screen
> Voltage. This situation wastes one of this rig's better resources namely
> modulator headroom. When altering the R.F. final's impedance through
> reduced plate current, the modulation transformer no longer sees the
> designed load.
> The correct way to reduce output power is to use an external plate
> supply with a Variac on the primary or switch the low B+ Voltage to the
> final (removing the high B+) through the accessory jack. Either way the
> high B+ is left on the modulators. This gives an immediate improvement
> to the audio as the modulator requirements are now cut way down without
> forcing the modulator into an unknown load. With the accessory low power
> mod, the rig will put out abour 12-14 Watts carrier which is a good
> level for driving quitea few linear amplifiers. Every available effort
> to clean up audio distortion should be considered when runnung QRO AM!
> Whom do I believe?
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