[AMPS] a sticky issue.

[Phil Clements]

> > Were I running a string of electrolytic filter caps on a 160 meter amp, I
> > would want a total of .01 mfd bypass capacitance at the base of the plate
> > choke.
> >
> > I found that even on the Alpha 77 series that 160 meter RF is abundant all
> > the way back to the line cord if additional bypassing is not done. The B&W
> > 800 choke is not too swift on "Top-Band."
> >
> > (((73)))
> > Phil, K5PC
>
> Hi Phil,
>
> I have three questions:
>
> 1.) What is the impedance of the choke in the AL-1500

I love these chokes...I buy them regularly for all my amp projects.
The one I have here in my hand is 219.7 uh...unmounted.
The first resonance is safely parked at 11.7 mhz.

> 2.) What is the impedance seen at the base of the choke
> referenced to chassis?

Can't measure that right now....but it is plenty for 160 meters.

>
> 3.) What difference do you expect to see?

I have never played with an AL-1500, but the amps I have a lot
of experience with (old Alphas et al, using B&W 800 chokes
on 160m. ( which are less than half of the Ameritron choke in value)

I find that  chokes of less value than about 150uh affect the tank circuit
in that the book values for the Pi or Pi-L don't work out because the
choke fouls up the L/C ratios in the tank with its interaction on 160m.

I see very little difference in the output, but I am not worried about that.
My concern is 160m RF getting back into the power supply and even
the A.C. mains.  As you know, 160m is a "whole 'nuther ball game."

>
> You must have the answers, or you wouldn't be able to make a
> determination of bypass requirements.


I have absolutely no Ameritron experience, nor do I want any!
It was done in the past on non-Ameritron amps using trial-and-error
until a minimum amount of RF was measured in the HV line at its
exit point on the deck.
>
> In my determination, the ripple in the supply at 1.8 MHz is about
> 1/2 of a percent when actual impedances are considered. Hardly
> enough to worry about.

That is very true, you have a lot of L working in the Ameritron choke.
That is the least of one's worries on the AL-1500. Both Henry and
Creative use 160uh and up; backed up by several 4700 pf bypass
caps at the base.
>
> What major performance changes do you expect to see, if the 1/2
> percent ripple is reduced from .5% to say .08 %? Or is this a "feel
> better mod"? (Nothing wrong with that, as long as it doesn't hurt
> anything else)

Henry, Creative, and I all "feel better" and it hurts nothing.
I am not concerned with performance changes as much as I am with
P.S. component protection and good engineering practice.


(((73)))
Phil, K5PC




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