GS35B 6m Amplifier
by K7CW
Click on callsign for K7CW web page

Right now, there are a lot of great Russian transmitting tubes available in Europe and the Far East at flea markets and from other private sources and they are relatively inexpensive. I recently decided to obtain some of these tubes and incorporate them into my station. I got some GS35Bs and GI7BTs. The GS35B is rated to 1000 MHz and its anode dissipation rating is 1500 watts. It is easy to build a grounded grid amplifier using this tube since it can be mounted directly to the chassis with clips. I have taken some photos of my progress building this amplifier. It's getting there, but I still have to come up with a few small parts for the dc circuitry. I have nine photos for you to look at:

Click on pictures for zoom

1. Bottom side inside the cathode compartment

2. Top side, inside the anode compartment

3. Major parts collection before construction began

4. The main Boxes. The RF deck goes inside the cabinet on upper right

5. The front panel starting to take shape

6. The GS35B with anode radiator removed. It is held down with heavy duty clips made from angle aluminum.

(Click on pictures for zoom)

7. The front of the amplifier. The big meters are from an old FM broadcast transmitter. The top meter measures 0-1.5A for plate current and the bottom one measures 0-500mA for grid current. The top knob on the right is for the loading capacitor, a 250 pf vacuum variable. The knob beneath it is for the plate tune capacitor, a 3-30 pf vacuum variable. The total dimensions of the RF deck are 11x11x11 inches (28x28x28 cm). I mounted a flange for air input on the back to pipe air from a remote blower to keep the noise down at the operating position.

8. A view of the top. To vent the hot air from the anode compartment, I am using a chimney made of sheet teflon (ptfe). A flange of the same diameter as the anode was brazed onto the anode compartment lid in order to attach the chimney to the lid. Some screening cloth was fitted over the top of the flange and secured with a large hose clamp.

9. A view of the back. The air is fed into the cathode compartment via a shielded box and a plastic flange fashioned from a 4-inch ABS toilet flange. The flange was inexpensive and a good fit for 4-inch dryer hose used to transport air to the amplifier. The flexible hose is going to be used as a union between the amplifier and the ABS pipe going to an adjacent room where the blower will be. The blower rating will be 150 cubic feet per minute.

I got the amplifier running, but went through a few trials and tribulations first. Now that I have it going, it runs like a champ! It's unconditionally stable. For those who are considering a similar amplifier, I recommend reading through the QRO pages on this site, particularly the article written by Bill, K8CU. Another wealth of information can be found on Rich, AG6K's web page.

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