[Boatanchors] 0A2 regulation...

[Gary Schafer]

You might try a milliameter in series with the VR tube to see how much
current it is actually drawing. Or a meter in series with the load then you
can calculate the VR tube draw.

73
Gary  K4FMX

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of Rodger
> Sent: Tuesday, February 06, 2007 10:26 PM
> To: boatanchors at mailman.qth.net
> Subject: RE: [Boatanchors] 0A2 regulation...
> 
> Hi Eugene,
> 
> The VR design assumes there will also be current load on the line in
> addition to what is "sunk" through the VR tube.  So there should be a
> minimum current draw of about 35 mils by the load and the VR tube will
> furnish the rest of the current draw needed to reduce the source voltage
> from 340 to 150 through 3K.  Effectively, the VR tube can be used in a
> circuit which has up to 30 mils of current draw variance by the load (i.e.
> transmit to non-transmit) so the ability to use the VR tube is not the
> total
> current needed across the dropping resistor but rather the load can never
> vary more than 30 mils without causing a problem.
> 
> Your actual frequency variance may be due to a drop in filament voltage
> during transmit which can cause frequency changes.  I recall that someone
> ended up regulating the heater voltage in their Heathkit SB-300 series
> receiver to avoid this and it was common in some of the older boatanchors
> to
> regulate oscillator filament current (NC-400, HRO-50, R-390A, etc.)  Some
> tubes are more susceptible than others to this so you might try
> substituting
> different tubes.
> 
> Hope this helps!
> 
> 73, Rodger WQ9E
> 
> 
> > -----Original Message-----
> > From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> > bounces at mailman.qth.net] On Behalf Of Eugene Hertz
> > Sent: Tuesday, February 06, 2007 9:09 PM
> > To: boatanchors at mailman.qth.net
> > Subject: [Boatanchors] 0A2 regulation...
> >
> > 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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> 
> 
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> $$ For vintage radio info, see the HCI web site $$
> http://www.w9wze.org