Re: Wanted WR90 WG16 Switch/Relay


Hi again Robin.

Yes, airflow is critical.  Do NOT run them with top or bottom cover off for any significant time, without some other means of pushing considerable air into the inlet, to cool the PSU.

The "Event Log" is often interesting to scroll back through. :-) Any TWT ARC events are a concern.

You don't need to "Thrash" them.  If they come into Operate/RF On without issue, let the tube warm up and stabilise, while keeping an eye on the "Iw" (Helix/Body current) indication.

If you lift the lid, and read the ratings plate for the TWT itself, that should give a fair indication of what should happen re Helix current.  Any more than the that indicated, something is not right.

However, the "Eb" (Collector) voltage shown on the front panel, will bear little resemblance to that on the tube rating plate.

The Tube gives Ek to Eb difference, the indicator shows Eb to ground (Helix) value.

(If it is a dual collector tube, sadly at the moment I can't recall which one is indicated.)

The Accelerating voltage (Ek) can be adjusted, as can any Grid or Anode voltage, but the relationship between Ek and Eb (1 & 2 if dual collector) is fixed in hardware.

The Filament "Ef" is also adjustable, and is (usually) close to 6.3V. Do not adjust!

(The Ef value may start low, while the Iw value is pinned at a limit, Ef will rise to the setpoint, then Iw reduce as the cathode warms.  That is normal.)

There are trips and warnings for all those, and usually Forward / Reflected Output Power, assuming they have built in directional couplers.

Warning levels can usually be adjusted from the front panel menu system, but trip values are set in hardware.

Take care not to over drive them, the SSPA's are not easy to source, & definitely not cheap!

Don't push the TWT beyond "Saturation" either, that (among other things) stresses the Helix thermally.

Have Fun.


Dave G8KBV.

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