TRANSMITTERS OF DAYS GONE BY

 

Viking Ranger on the top right and SX-100 on bottom left.

Viking Ranger on the top right and SX-100 on bottom left.

I miss the vacuum tube. Oh I am not saying the vacuum tube equipment better then modern solid state equipment. If I believed that then I would have to clean out my shack and replace most of my equipment.

Vacuum tubes just had something that solid state does not have besides a lot of extra heat. I can’t explain it but maybe it is just an old man remembering where he came from.

6146

6146

When one looks at the price people want for vacuum tube equipment on Ebay it would appear that there are several people who still have an interest in them.

With so many transmitters today the operator can just set it on frequency and, if the antenna is resonate, start transmitting. No adjustment is necessary. That was not so with vacuum tube transmitters especially those with class C amplifiers. The class AB and class A amplifiers used with SSB transmitters were usually not quite as complicated.

When the operator of a vacuum tube transmitter changed frequency first it was necessary to first check the final place current and Elmac AF-67 transmitteradjusted the plate capacitor for a dip to minimum plate current. Then the grid capacitor and driver controls were adjusted for a peak in plate current and the final amplifier capacitor was again adjusted for a maximum dip in plate current. The plate load capacitor had to be adjusted so the plate current was maximum while the plate capacitor was readjusted for minimum plate current and the grid capacitor was set for maximum current. (Thus the term, “dip the plate and peak the grid.”) The drive was adjusted so the final plate voltage times the plate current equaled desired transmitter power.

It was very important that the operator properly adjusted the transmitter because improper adjustments could result in reducing the life of the final amplifier tube and other components. It could also result in superiors and/or harmonic radiation.

I remember one transmitter we had to learn how to adjust in Coast Guard Radio School that did not have a final amplifier plate current meter. There was, instead, a window that allowed the operator to see the final amplifier’s plate. When the transmitter was operated the plate would glow a cherry red and that meant it was operating at the proper current level. The place capacitor was adjusted for minimum brightness and the grid capacitor was adjusted for maximum brightness.

If you become the proud owner of a vacuum tube transmitter, before you put it on the air, find someone with experience to show you how to load it or if you have the manual carefully read the operating instructions and follow them to the tee.

Share on Facebook



This entry was posted in Amateur radio, Ham Radio, Vacuum tubes and tagged , , , , , , , , , , , , , , . Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *