It seems that the exchange of GU74b / 4CX800 tubes in Amplifiers like Alpha91b, Acom2000A, and Acom1000 is more interested than originally expected. In my post on how to replace the tubes of an Alpha91b I explained in depth why it is so important to recondition, to “getter”, the tubes at least 24 hours before any other voltage can be applied. Often amplifiers apply automatically HV and grid voltages which makes them unsuited for the gettering process. My Buddy Matthias, DK4YJ built recently a simple device that makes the heating and testing of tubes much more convenient.
A friend of mine recently was very generous and sent me four used 4CX800 / GU74b which he didn’t need anymore. The tubes were traveling a while and through several non-EU countries. Today the parcel finally arrived. I have already heard wild stories about customs, but I didn’t expect this: Customs drilled holes in two tubes and later opened them with a saw. Check out the pictures.
In preparation for the upcoming CQWW 160m Contests, my friend Hannes, DK1NO was so kind to give me one of his W7IUV broadband, high IP3 preamplifier. Thanks, Hannes! Without knowing the exact performance data, I ran a few measurements with my Network Analyzer on the amplifier to determine the Gain and its operational fitness. Read on for measurement results and additional notes on how to measure active components.
It finally happened… After a decade of reliable service, my Alpha91b amplifier broke. Most likely on its way to Spain one of the tubes broke. During the commissioning at ED1R, fire & smoke shot out of a chimney. The first shock was big, but a few measurements confirmed that just the tubes were broken. In this blog post, I will share the knowledge I gained during debugging, commissioning, and breathing new life into the amplifier.