6229 Magnetron Experimental Basic System Prototype II
8.9-9.4Ghz
The photo at the right shows the complete 6229 magnetron expermental system that is completely portable powered a 12 volt 22 AH battery. The magnetron's peak power out is approximately 800W that tunable from 8.9-9.4Ghz.
How this project got started
During the late 50s to mid- 60s from grade to high school I would shop the electronics surplus stores to get parts for my science fair projects. Sometime close to mid 60s I bought a 6229 magnetron for a few dollars. Afterwards for more than 30 years the 6229 magnetron remained in my electronic junk box. About 6 months ago I saw it and decided to give it life. This page gives a description of the design and construction of the latest 6229 magnetron experimental system that I built.
X band RF exciting a neon bulb
BELOW: Photos Showing Various Views of the Experimental System
Designing the Pulse Modulator
Having no technical information for this magnetron I decided to do some Web search before designing and building the pulse modulator.
The Vintage Technology Association
http://www.decadecounter.com/vta/tubepage.php?item=20&user=0 provides some
specifications for the 6229 such as its peak power of 700 watts at 250 ns pulse width, it is tunable from 8.9 to 9.4 GHz and "used
in the Nike I missile guidance unit". When I did a search on the 6229 magnetron and Nike I missle unit I got the Nike I
System technical manual from
http://ed-thelen.org/index.html#TM9-5000-28. I got all the information that I needed
and decided to design my pulse modulator to the same specifications. The step up pulse transformer ratio of 275 volts in to 3,900
volts out; magnetron load impedance of 5,500 ohms and reflected transformer input of 28 ohms; that the PFN is charged to 550
volts Also I found on the Web prf1ss1329.pdf ?PERFORMANCE SPECIFICATION SHEET ELECTRON TUBE, MAGNETRON, PULSE TYPE 7521
which I believe is OR is almost identical to the 7521 magnetron; its heater specified from 4.5 - 5.5 volts.
given => Vout/Vin = 3.9KV/275V = 14.18 & Zout/Zin = 5.5KW/26W = 211.5
comparing to calculated
ie PWR = V^2 / Z ==>> PWR IN = PWR OUT
Vout^2/ Zout = Vin^2/Zin =>> Zout/Zin = Vout^2/Vin^2
given
=> Vout/Vin = 3.9KV/275V = 14.18 ==>> (14.18)2 = 201 close to 211
I decided to keep the transformer turns ratio in the 14:1 range and use this for computing the PFN impedance when using the 7521 magnetron
for comparison purposes.
Using the Rayleigh line PFNdesign formulas given at the ?Ness Engineering Technical Data Pulse Forming Network (PFN) Circuits? Web
page:; I decided to increase the pulse length from 250 to 400 ns.
Assume PFN Z = 25W; 5 stages ; T one way is 200nsec then
L = ZT/N = 1uH C = T/NZ =
1.6nF
Looking in my parts bin I decided to use three ceramic 560pf @ 3KV in parallel giving 1.68nF for each of the five sections.
Z is now (L/C)0.5 = 24.4 ohm
Part 1
PFN Design: