Serial no.: 322326

A tube YAESU transceiver with one frequency conversion.

It's a 1973 tube YAESU transceiver with one frequency conversion. The intermediate frequency is classic - 9 mHz with a quartz filter for that frequency. Details foxtango. I bought thetransceiver from one polish internet auction - allegro. It was said that everything worked fine, but when I finally got my hands on it, it turned out that the transceiver is not sensitive, S- meter is immobile and the output has only a few watts. After some testing, I noticed that the power amplifier tubes 6JS6A were burnt-out. Only by using all devices from my radio laboratory I found out that it had a really rare technical fault.The 1 MOhm intermediate frequency tube bias resistor was broken. After replacing it the transceiver started working again and was easily adjusted according to the service manual. It was unusual but, believe it or not, all of the original japanese tubes were still working. It wasn't hard to make a backup set of tubes. I even managed to get my hands on the very rare 7360 tube - a balance modulator. It wasn't that easy with the PA rearmost tubes though. It was a lot worse, I couldn't find them even on ebay. After comparing the parameters it turned out that there is a complete electric replacement and only the construction was a bit off. It was the GU50. 12,6V heating was fine, the anode voltage rising up to 800V was intended. I had to take the GU50 apart, lower the montage capacity and connect the anode voltage to the tube's socket. I raised the grid voltage up to 300V and the power amplifier started working as it was supposed to. The output was from 110 to 140 wats, dependent on the band. You can see the modifications made on the amplifier in these photographs. Top view, Bottom view. A few photos from the construction: front, top, bottom.