CHECKING TUBES IN AMATEUR SSB RIGS

CHECKING TUBES IN AMATEUR SSB RIGS

Did you know that if you have a tube transmitter or transceiver, that you also have the best tube checker in the world built right in?

Given that tubes are becoming more scarce and thus more expensive, it makes economic sense to change them only if needed; this will save you money AND help preserve the supply of tubes, which will help keep future costs down a little.

So how do I do it?

Here's the method that we use here at the shop, and you don't even have to take the cover off the rig!

	USING A DUMMY LOAD, tune the rig up for "max smoke" as usual.
	Unkey and switch the meter to ALC. Drop the CAR control so that ALC is mid-scale. Some rigs ALC may not work this way however.
	Watching the ALC meter indication, key up. Meter should come up midscale and hold or perhaps drop off very slowly.
	This would indicate a good driver tube.
	If the ALC meter comes up, then drops off quickly, you have a bad driver tube. The quicker it drops off, the "badder" the tube.
	Now to check the final tubes. Reduce drive to zero with the CAR control, or switch to SSB with the mic gain all the way down.
	Set the meter to read plate current, or Ic.
	Key up and note normal bias current (50-60mA for most rigs).
	Unkey.
	Locate the bias control. TS530-820-830, on the lower rear panel corner closest to the finals and ant conn. TS-520, left side under access panel. FT-101 et al, inside the rig somewhere.
	INSULATED SCREWDRIVER on bias control (if inside rig)...or hand... now key up, and quickly turn bias control ALL THE WAY UP for MAX PLATE CURRENT. Note current quickly. Watch for 1-2 seconds and then IMMEDIATELY UNKEY. Did it come up and stay, or did it come up and then drop off? Did it drop off rapidly? Do it again if you have to, 1-2 seconds ONLY. You may need to read through this a couple of times to "get it". That's ok.
	If the plate current came up and STAYED, and was above 150mA, the tubes are good. If the current came up to ANY LEVEL and DROPPED OFF RAPIDLY, they are bad. If the current came up and stayed but was below 150mA, you have one or more final tubes bad*.
	Finally (sorry, bad pun), reset your bias to 50-60 mills and then retune for max output. If you see 100 watts on 20-80M and 75 to 90 watts on 10, 12 and 15 meters, be happy and get on the air. If power output is half that, using what you learned here, order a NOS set of tubes for your rig. I use RF Parts and some ebay vendors (sorry, my secret as to whom!).
	Not that hard, eh? This is essentially the same procedure that I use in my shop (but throw in a neutralization adjustment, cleaning the PA enclosure, checking the plate blocking condensor and plate choke bypass caps for heat stroke, lubing the fan, etc)