4CX800 2m Amplifier


2m amp and HV powersupply


Rear view of amplifier

Output circuit; right to left: tx relay, lowpass filter, directional couple. The input relay is mouted on top of the LPF.

Underside view of amplifier. From the top left corner; line filter, screen relay and ballast resistor, to the right of that is the HV sampler for the safety cct.
Bottom left corner is the prototype G3SEK screen regulator. Bottom center is the safety logic, with the heater regulator above it. The small board above it is
an interface between the low-level ptt line and the 28v relay supply. Bottom right is the grid bias supply.

The tube with the chimney made from 25mil teflon. Partial shot of the plate line and tuning capacitor. Note the use of the shield from some
RG174 as an RF gasket around the plate compartment. The length of the plateline, from where it connects to the tube to the center of the grounding pillars, is 163mm, not as given in the Svetlana article.

A closer view of the tuning assemby, with the reduction drive on the left

Grid circuit. This has been changed from the original article to give a more flexible match for different rigs. It is a series tuned circuit, with a 1 turn
link coupling. The coil is 3 turns with ~3/8 id. The coupling loop is about halfway meshed. I dont recall the value of the tuning capacitor, but it should be easy to work out what is needed to get resonance.

A view showing the cathode circuit. A hexagonal brass plate, grounded in 8 places, with the 4 cathode connections soldered directly
to it. Gives a good low inductance ground. connections to the grid, screen and heater are via holes in the plate.

A not very good view of the output coupling circuit, note this taken from the other direction compared to the other images. The circuit in the original article worked fine, but it was suggested by someone in DL-land thata link coupling was more efficient. I tried it and didn't find much difference, but as it worked I left it alone. The link is approx 25 x 45mm, and is about 5mm away from the plate line. In this view the grounding pillars can be seen, 4 of them.

Maintained by: nu8i@cox.net
This page was last updated on 15Feb2004