[Amps] B&W PT-2500A on 10m?

[Jim W7RY]

I can send you a picture of my B&W PT2500 that has 10 meters in it. There is 
a small air core coil and a couple of caps on my 10 meter input. Let me know
73
Jim W7RY


-----Original Message----- 
From: bob
Sent: Thursday, April 03, 2014 2:36 PM
To: amps at contesting.com
Subject: Re: [Amps] B&W PT-2500A on 10m?

I think we got off the rail a bit with respect to the history of the
PT-2500A which has been discussed elsewhere at length.    While that is
interesting, I need to get back the primary objective -

What is the best way to get the stock amp back onto 10 meters???

Thanks to both Dick W1KSZ and Tom W7WHY for responding with what turns out
to be the same information (from separate sources, but same text) suggesting
that only the 10m input need to be installed to get it working on 10m (a
good thing).

Both references suggest adding a single 133pf (100pf & 33pf in parallel) cap
with a coil of 6t of 18ga wire, loose spaced (about 5/8" long ) on  .500"
diameter.  However, this yields a C-L only solution for the tuned input.

Yet, the schematic clearly shows a PI input network (C-L-C) for all the
other bands where this article suggests a simple single C-L section (I have
the original printed manual and schematics if anyone is interested, I have
them on PDF soft form as well.)

Any thoughts?

Anyone recommend a PI (CLC) solution with values or have any idea of the
factory update kit for 10m ?

I am getting frustrated by some of the Pi matching calculators I have found
on the web since I get rather large differences (20-100% diffs) in the
calculated outputs from them with the same inputs, and because of that, I
have little confidence in them.  This is rather surprising.

I was using 50 ohms in,  and 60-65 ohms out (for a pair of 3-500Z's) for
Rs/Rl respectively @ 28.5 mhz with a Q of 2 or 3.

Any idea of jXL reactive component of the pair of tubes?
Is my choice of 60-65 ohms fair for the input of the pair?

What is my feeble mind doing wrong?
Anyone got a spreadsheet or online calculator for input matching you have
faith in?

-bob





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