GATES 500 Watt A M modification

[DMOD]

Okay, one more comment from me.  ALL I am going to change is the transmitter output circuit.  The transmitter will currently run in the ham bands and do 500 watts carrier AM with no problem.  
ALL I want to do is change the output network. I will be running only on 3,880 and 3,885.

These items may help

https://frank.pocnet.net/sheets/049/8/833A.pdf

Phil - AC0OB

Another online calculator is:

http://www.ee.oulu.fi/~timor/javaa/matcher2.html

Use the following input parameters:

Source resistance = 4800
Source reactance = 4.8e3
Load Resistance = 50
Load Reactance = 0
Q = 12
Freq = 3.88e6

Results seen in the "Low Pass Pi Matching Network" is:
L ~ = 14.4 uH
Csource (Plate Tune) ~ = 128 pF
Cload (Ant. Load)  ~ = 782 pF

The point is, look at the various results and make your three elements Variable enough to work over the range of values shown.

Phil - AC0OB
 

[WD5JKO]

We seem to be dancing around what the input circuit consists of, and whether or not the 833 will be neutralized.  As Steve QIX correctly pointed out, the 833 will need to be neutralized. A swamped grid like that linear circuit will not work if you plan to run the 833 as a class C plate modulated amplifier due to the high peak grid swing required, and deep negative bias.

Some napkin doodle shows the 833 plate grid capacitance, around 6 pf to have an Xc of ~ 4K at 40m. This will be too much to ignore unless you wish to run a modulated oscillator.

With a pi network output, that eliminates plate side neutralization like they do in a BC-610. My first post in this thread had a link to another post by W8ACR on how he tackled the issue using a big triode final.

Good luck with this project..

Jim
Wd5JKO

[DMOD]

For neutralization, I would simply adapt the system used in the BC-1J:


Phil - AC0OB