G1-ALC

TetrodeBoards

The Tetrode Boards by Ian White, GM3SEK. Redesigned with KiCad.

In 1998 Ian White, G3SEK, nowadays GM3SEK designed control and protection circuits for RF power amplifiers that use tube tetrodes. These boards were sold for many years by the designer but were retired around 2017 and are no longer available.

The manuals are still available however, and that documantation is excellent.

After my retirement as a system developer I found time to return to the VHF DXing that I used to do as a student in the late 1970's. By then one of the things I built was a VHF power amplifier, described by Fred Merry, W2GN, which was used even for some EME contacts until around 1987 when a storm took my antenna. Since then, the amplifier was only used occasionally.

Now, 37 years later, the ham world has changed quite a lot. Nowadays computers make the waveforms and almost every ham has a spectrum analyzer built into their radio. My signals from the old PA didn't look very good there.

Actually it is probaly at miracle that the PA and its power supply worked at all now. There were lots of electrolytic capacitors in the power supply that were surplus already in the mid 1970's, and when I got reports on hum on my signal, I checked these caps. I had only about 8 uF left and the G1 and G2 voltage varied too much to be happy with.

That's when I found out that these tetrode boards could help, but since the boards were no longer sold, I decided to try to re-engineer them using KiCad. This time using methods available today. Thus this design uses SMD mounted components and professionally produced boards. I have some boards left, so anyone who likes to try building on these boards can have them for the expense of postage. Beware though that they have issues. Check the issues tab at GitHub first.

A crucial component in Ian's design is the 748 op amp. These are no longer manufactured, but they are available at eBay. Luckily for me, I found a few 748 IC:s leftover from the happy '70s in my old junkbox.

Christer Bernérus, SM6FBQ. JO67BQ 2024-04-04.