Mirko Voznjak, YU1AD and Mike King, G3MY
Issue 55 Six News, November 1997
Mirko, YU1AD writes:
I am writing to give information about a very special Russian-made transmitting valve, named Gi7B (sounds like some special event station from Northern Ireland!). This is a coaxial-type valve, apparently developed to be primarily used in radar systems, but it is very useful for any frequency from zero to nearly 3GHz. It is a valve with ceramic insulation (pink colour!) and has a substantial heatsink at the anode connection. You can see the valves outline and the set of characteristic curves, in figure 1. Other electrical data are given in table 1.
Table 1: Gi7B valve data
It is a directly heated triode, with the heater connections on
two bottom round-type connectors, so it can be easily connected
with the aid of appropriate shells. Above that is the grid
connection, which fits a brass or bronze machined flange fixed to
the chassis with, say, four M3 screws, giving a very good ground
connection for a grounded grid amplifier. Above that broad round
area, below the heatsink, is a silvered metal connection for the
plate, which could be realised with an appropriate shell.
Naturally, this valve requires forced air cooling, with a good
squirrel fan, to blow the part of the valve which is above the
Figure 1 - Gi7B valve outline and characteristic curves.
Up to this moment it might sound like a fairy tale, until we discover how cheap and easily obtainable it is. A Yugoslavian ham, who runs his own trade business, has about 100 of them available to be sent the UK (note that Mirkos letter was written in May 97 - Ed).
Figure 3: G3MY's cooling chimney - a flower pot!
With each shipment you will get a photocopy of an article from
the Hungarian magazine Radiotechnika describing a
linear for 144MHz with complete schematics, plus the drawing of a
mounting flange which has to be turned on a lathe. One tip:
after making the flange to fit the grid area of the valve, make a
vertical cut in it and after dropping the valve in put an
appropriate shell around the flange with the facility to tighten
it with an M4 or 4BA screw. That will keep the valve very firmly
in place and ensure solid grounding of the grid.
The address for ordering is:
Imre Salgo, YT7RIT,
Mike, G3MY has a daily sked on 14MHz with YU1AD. He has
bought four of the valves, and writes: