[Amps] Power tube tester

[Bill Fuqua <wlfuqu00@uky.edu>]

	Well, I have gotten back to my 5 year old project. Hope to have it ready 
to show our local radio club on Monday. This project is a portable 
transmitting tube tester. It has sockets for 6146 ( and it's relatives), 
small 4 Pin Triodes (such as 811, 25T etc) , 4CX250B ( and its relatives), 
8072, 8122 and 4-1000 tubes. I will have adapters for 3-500, 4-125, 4-250, 
4-400, 8877, 3CX3000A7, 4CX1000, 5CX1500 and bayonet type of smaller 4CX 
tubes.
	By portable I mean that it runs off 12 Volts DC and is in a Hickok tube 
tester case ( not including adapters).

It will perform pulse test of the tubes up to 20 amps plate current and 5Kv 
plate voltage. And can will do gas test as well.

My smaller one has worked well for some time but had to redesign it to 
withstand tube breakdowns. It seems that some tubes don't arc over until 
you apply filament voltage and have them conduct current, then BANG. 
Unfortunately, my original one required almost all the semiconductors 
replaced after such an event. Gets expensive when you are using high 
voltage power P-channel mosfets to drive the grid.

The test parameters I use are simply points taken off the characteristic 
curves for the tubes. I shoot for a high current moderate plate voltage 
point on the curves which in many case require a positive grid pulse. I set 
the grid pulse height value, along with the  plate voltage, screen voltage 
and filament voltage or current. So far I have found that all the new EIMAC 
tubes I have tested are right on the money or a few percent higher in plate 
current.  Aged tubes are obvious and also it is easy to match tubes as well.

There is one thing I'd like to do that I can't with a portable tester. 
There is a life test that requires a lot more plate power ( can't simply 
pulse the plate for a few microseconds). And obviously would drain the 
batteries and require more than a power supply capable of a few ma of 
continuous current.  But thus far it seem that tube age is apparent by just 
comparing the tube against the characteristic curves.

One thing this tester will allow me to do is to get a set of characteristic 
curves for a triode connected tetrode such as a 4-1000. That  would be 
useful perhaps. I have not seen data for triode connected tetrodes or 
pentodes other than some  RF amplifier amplifier empirical data.

Since I am looking into retirement I wonder if there would be a small 
market for such a tester. I have other projects in the works but they are 
mostly education related.

I have considered making a pulse curve tracer but the thought of connecting 
a computer to a device that may have an artificial bolt of lightning  (tube 
arc over) once in a while is a bit scary.
Any thoughts?  There are also safety issues in regard to possible exposed 
high voltages. It could have as much as 7 joules of discharge energy which 
could stop an heart beat.

73
Bill wa4lav


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