[Boatanchors] 0A2 regulation...

[James Duffer]

Turn off the equipment, remove the OA2, measure the resistance of the 20 
watt resistor.  What do you measure in Ohms?


>From: "Eugene Hertz" <ehertz at tcaf.org>
>To: boatanchors at mailman.qth.net
>Subject: [Boatanchors] 0A2 regulation...
>Date: Wed, 07 Feb 2007 03:08:56 +0000
>
>Hello all,
>
>Several of you were very helpful to me on my last round of questions 
>regarding the operation and testing of this tube.
>
>My problem was whenever I keyed the transmitter the CW frequency could 
>shift 200-300hz in a space of 20 seconds or so. And while I am unlikely to 
>send a 20 second long daaaahhh, I noticed that any word in CW might start 
>and end on noticeably different frequencies. The manual (ce 100v) states 
>that after 5 minutes warm up, frequency stability should be 25Hz.
>
>So here's what I did. I bought a tube extender that allows me to connect a 
>voltmeter to the pins of the tube.  I tested 8 different 0A2 tubes I had 
>under two main conditions "in circuit". First, I varied the input to the 
>transmitter from 110VAC to 120VAC to see which tubes gave better regulation 
>from the house voltage. Second, I measured regulation under key down 
>conditions.
>
>Testing each tube for varying house voltage using a variac resulted in a 
>wide range of regulation, the best being 1VDC and the worst tube being 
>6.7VDC. According to the tung-sol data for this tube 2v regulation should 
>be acheived with 5-30ma of current. However, Amperex data sheet says 6V 
>with 5-30ma.
>
>I then tested these 8 tubes with 120VAC input and key down into a dummy 
>load (about 90 watts into the load) and measured the variation in regulated 
>voltage.  The range here of the 8 tubes was 0.6V to 4.6V.
>
>So, I will certainly try the tube that only varied 0.6v when keyed down. I 
>have not taken frequency measurements with that tube yet.
>
>So here's my academic question: The circuit shows a +340V supply line with 
>a 3K Ohm, 20W resistor in series with the anode of the 0A2. the cathode is 
>grounded. At the anode of the 0A2 is then the 150Vdc output line.  Doing 
>some calculation, 340-150=190V across that resistor. Dividing by 3K Ohms 
>gives a current through the tube of 63ma. But the tube is rated for a max 
>of 30ma, so this doesn't make sense.  I then began to think about the 
>non-trivial heat generated by these 0A2 tubes and thought to myself, "self? 
>That heat must mean the tube has some equivalent series resistance" Which 
>would make the 63ma somewhat less.
>
>How does one properly analyze this circuit? How does one calculate the 
>resistance of the 0A2 to properly calculate the current through it? Perhaps 
>I should calculate I=340/(3000 + Rtube)?
>
>Thanks!
>Eugene
>
>
>
>
>
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