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toptone: IN-13 Analog Bargraph shows signal strength

Martin Renz Ernst Erb Vincent de Franco Martin Bösch Mark Hippenstiel Bernhard Nagel 
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Forum » Radios and other type of sets (Physics) etc. » RADIO MODELS DISPLAYED » toptone: IN-13 Analog Bargraph shows signal strength
Joe Sousa
Joe Sousa
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08.Feb.09 01:55

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I have  added the Russian IN-13 analog bargraph neon indicator to a classic 5 tube AC/DC radio. The IN-13 indicates signal strength and makes tuning more precise.

The IN-13 is the modern version of neon tuning indicator tubes used in the 1930's, like the Tune-a-lite tube in a FADA radio with the RW chassis, or a similar tube in a Cossor radio.

But the IN-13 offers much better performance with a specified linearity of 2% and a much crisper plasma shape up to 10cm/4in long. The gas is neon, so the glow is orange, but a purple glow can be obtained from some IN-9 types.

You can see a photo and video clip of the completed IN-13 setup.

The schematic is also available at this link and in the RMORG archive for the 5M-100 Topline/Toptone radio.

The IN-13 plasma fires around 120V and drops 100V when it is on. The 100V drop is independent of current up to 5mA, when the plasma is at full 10cm length. Further current increase bightens the full lenght, and the internal drop rises rapidly above 100V.

The IN-13 senses the load current variation in the 12BA6 plate current that results from AGC action. A strong signal reduces plate current, and this current is fully absorbed by the IN-13. a very strong signal makes the bar go to full lenght. and even weak signals shows some increase in plasma lenght. Without a signal present, the plasma lenght is 1cm or less.

The IN-13 operating range is set by the new power resistors added in the B+ supply. I chose to use 28V 40mA bulbs for these resistors because they reduce the effect of mains voltage on bargraph plasma length. These four light bulbs in series, only drop around 30V, but they do a good job of rejecting 10V of line voltage variation.

I added a 1k resistor in series with the existing 1k resistor, to power the 12BE6 and 12AV6. Perhaps I should have connected the 12BE6 screen pin6 to the 100V drop that is regulated by the IN-13, and improve oscillator stability of the 12BE6. This is an afterthought.


The 1N34 diode and 100k resistor were added to insure startup from the higher B+ supply around 135V.


The schematic continues in the next figure to show the connection to the 12BA6 IF stage plate. Note that this radio came with a single tuned circuit at the IF output.


This shot shows the final wiring for the IN-13. The bulbs glow red and regulate current to the IN-13 and 12BA6 IF stage. The two extra caps reduce hum and interference. The red-blue wire drives the anode and cathode of the IN-13, respectively.

Comments invited,


This article was edited 07.Apr.12 00:25 by Ernst Erb .

Rolf Nickel
Rolf Nickel
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18.Feb.09 19:47

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Dear Joe,

I think that your idea is fascinating because this special indicator tube is an alternative to the magic eye and, additionally, to the small needle indicator instruments which are typically used as signal meter or tuning meter.

The tube IN 13 can be obtained from e. g. the ajf company. I got the permission from Dipl.-Ing. Jan Wüsten to publish some details and pictures from the data sheet which he provides on his website.

Unfortunately, the main description is in Russian language, and I am not able to translate this. Maybe, one of our RM friends from Russia or Eastern Europe will do us this favour. Meanwhile I asked a colleague from Eastern Germany (the former DDR /GDR) who learned the Russian language in school. He gave me today a "rough" translation, which I hope to publish soon.

Best regards

Joe Sousa
Joe Sousa
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19.Feb.09 03:34

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Dear Rolf,

Thanks for the extra information on the IN-13. It will be helpful for builders.

At this point, I should clarify the difference between the IN-9 and the IN-13

The IN-13 takes up to 5mA for a 12cm orange glow from Neon gas, and has three electrodes. One  perforated cylinder as the anode, a central wire cathode for the glow, and a short pilot cathode to start the glow.

Most IN-9 take up to 10mA for a 10cm purple glow from Argon gas, and only have two electrodes.

But some IN-9, like the one used in this thread, are filled with Neon gas and glow orange, but the current rating and size are still same.

Confusion between the two glow colors caused me to make a mistake I made in this thread: The tube you see in this thread is a 2 pin IN-9, not a 3 pin IN-13.

In terms of application of the tube, the two glow tubes the significant differences are the maximum current and the extra pilot cathode for the IN-13. The strike voltage around 120V and sustain voltage around 100V are similar among all three tubes.

The IN-13 has twice the sensitivity of the IN-9, so this should be taken into account when applying the tube. If the glow swing is too extreme, some resistance in series with the tube can be added.

The pilot cathode of the IN-13 requires a small current to insure that the main cathode starts properly. This negative bias could be obtained with a 100-500kOhm resistor to the grid circuit of the local oscillator. The grid of the local oscillator, usually develops around -10V, which is enough to supply up to 100uA into the pilot cathode of the IN-13.

The extra -10V of bias at the pilot cathode of the IN-13, eliminates the need for the startup circuit with a diode and resistor, which I included in the circuit above for the IN-9. This was necessary because the low B+ of an AC/DC 117VAC radio may not guaranty the starting voltage for the two terminal IN-9.

Best regards,


Michael Watterson
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10.Oct.11 10:15

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Images of magic eye types and overview of types

How the "Tune-A-Lite" works

How the Magic Eye Works

The Russian Neon/Argon Bargraph IN-13 (there is a less sensitive IN-9)

and History of Tuning Indicators

Here is an overview of Vintage Electronic Indicator technology (not just "Magic Eyes"  or "Tuning Indicators")

This article was edited 11.Oct.11 22:48 by Michael Watterson .