50MHz 2 x 4CX250B Amplifier GW4RWR

Introduction
This was originally a university project, designed from first principles in 1989. I wouldn’t recommend construction of a twin tetrode amplifier. The additional power supply circuitry needed isn’t worth the effort for just 3dB more power. Rather find yourself a bigger valve in the first place. I only bothered since GW4HBZ had given me five valves to play with. Do yours glow blue/green when you look down at the anode vanes in a dark room? I was scared that there might have been X-rays coming out as well. Still, I've managed to reproduce myself.

Results
2.7kV on the anode gave 770W o/p.

I used a JetStream 850 vacuum cleaner as a blower for those first tests. For those who haven’t seen this little monster, it’s a 50cm tall drum, with a motor on top. It can suck or blow, depending on where the pipe is placed! The noise was so awful that everyone in the house complained. They soon learned that I wasn’t vacuuming the shack carpet. I wore agricultural ear protectors for the tests, and a David Clark HT10-40 noise cancelling headset when I went on air. The transformer bolted inside for screen and grid supplies was a ridiculously heavy 405-0-405V 450mA. Despite using just a three element yagi, I got replies from everyone I called, first time, with this ugly brute.

Conclusion
It's dead and buried. It was hideous within, but very strong. Aluminium front panel for easy drilling, but the rest of it was welded steel; I could jump on it quite safely, and often used it as a stool. It was slowly cannibalised for other projects and before the hull was scrapped.

I’m afraid that I lost interest 6m. I know it's everyone's "magic band", but I found it more like 28MHz than VHF, and felt that I might as well be on HF anyway.