deel 2

This project involves the building of a 2 meter (144Mhz) amplifier. Design is to
use a tube, much easier then using some transistors, tubes can handle a mis-match better
and perhaps the building of the thing is cheaper as buying one,..with the same power output.

After searching the internet I found a article from UKW-berichte from March 1977, this
is a german magazine. German amateur DK1OF made a nice design with layout and explanation
of building this amplier, tube used is a 4CX250B and estimated power output 400Watts.

Here the PDF file of the original article

Costs till now:

4cx250 + base + chimney 1   56,20
1,5mm copper for cavity 5   61,50
M3 x 10 brass bolts 10   0.15 p/st
M3 brass nuts 4   0.09 p/st
Snail-shell like fan 1   13,50
Axial fan (220V) 1   gratis
Elko`s 470F/450V (105c.) for power supply 10   24,00
Elko`s 330F/450V (105c)  for power supply 10   16,00
Resistors, capacitors, diodes.  for power supply and cavity cavity x   72,00
High voltage trafo (600V, 800V, 1000V, 1200V, 0, 1200V,1000V 800V, 600V - 1KW) 1x   105,-
Hoogspannings elco (50F/4000V) 1x   35,-
Silvernitrate (not all 200grams needed) 200grams 80,33
Panelmeters (1mA/300Ω) 3 9,50

The copper I have is cut to size where I bought it, so I can go ahead as soon I was home again. To draw onto the copper
I cleaned it first and put some indian ink and let it dry. This way you can put nice drawings on the copper without damaging it.

drawings on copper


Insides of the cavity completely assembled,..all made out of brass


Cavity 15-3-2008
The fan is just put against the cavity to see how it looks,..a nice
big one and enough capacity, I also have a smaller one.


6 April 2008
Coupler to the output plug with capacitor.


Turned base clamp

impression of front of amp.


Cavity in constuction


Now the cavity is finished, only has to get a nice silver finish inside,..the high power side that is, I got a luxury problem here. The high voltage transformer has 2x4 outputs of
600-800-1000-1200volts, and this 2 times with 0 in the middle. If I got the right decked switch here I can switch from 200 volts to 2400 volts in steps of 200volts. This way I can play with anode voltage to give more/lesser power output.

The transformer is coming from number "TRF-1602-26", here I also bought the high voltage capacitor of 50F/4Kv.

Here the schematic of the transformer towards the decked switch I now have, I didn`t put the 200-400 volts position not in the drawing as I don`t think I need these for the amplifier, I think below 1000volts is not needed, but it`s wasted not to use these.
I also could do this using a variac in front of the transformer,..but I don`t have one I don`t want to spend the money for it.

will be updated.....