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Old 11th July 2004, 11:27 AM   #1
adalin is offline adalin  Sweden
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Default Strange Tube

Hi this is my first post at this forum so be gentle...



I am currently renovating some old tubegear and came across a strange tube.

Its broken so I need to replace it but the problem is that I dont know what it is..

Its marked:

G1S11

"STANDAR"

"SVENSK TILLV"

And inside the tube its painted in white "HT 49"

Its like 3" tall and 1" in diameter


The internal structure is made of two small steelpins and something that looks like a heaterwire with a thin wire around it. But the wire is burned of so its broken.

What is this tube?

It could be a lamp.... But what if its not?

Included is a poor scan if it..
Click the image to open in full size.
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Old 11th July 2004, 01:26 PM   #2
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Hi,

It is probably a balast tube or "barett", it is constant current device that is used in series heater chains to take care of additional voltage drop. It consist of a iron wire in hydrogen gas, when the iron wire heats up the resistance is increased so the current goes down, the iron wire gets cooler aso until it reaches a equilibrium where the current is almost constant.

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Old 12th July 2004, 06:50 AM   #3
adalin is offline adalin  Sweden
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OK so its a ballast tube then...

Is there any way to replace this tube with a semiconductor?

Or can I just skip it and wire the two cables going to the tube
together?

Is it a vital component?
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Old 12th July 2004, 07:19 AM   #4
adalin is offline adalin  Sweden
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A resistor would be a good replacement perhaps?

The only problem is that if it were a ballast tube. What voltagedrop did it have?

can it be 11v? or is tis value to low?
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Old 12th July 2004, 08:29 AM   #5
dhaen is offline dhaen  Europe
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Default baretter

It's not so much the voltage drop, as the heater chain current you are interested in. Check the heater current of the valves by looking up their spec's at Frank's tubes . It'll be in the region of 100 to 200mA I think. Then add up the total heater voltage (the valves will be in series). now do some calculations....

You can also do soeme google research using the keywords: baretter & balast
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Old 12th July 2004, 08:36 AM   #6
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It is not recommended to replace it with a resistor as a balast is a constant current device. The current value of the original barett is dependant on what kind of tubes that are used, U series tube are for 100mA and P series for 300mA.

Depending on the number and type of tubes type in the heater chain the voltage drop can be quite substantial so it is not so easy to replace it with a series resistor. Try to search for the tube data in TDSL and calculate the total voltage drop, then you can calculate the drop in the barett and design asimple constant current solid state replacement.

A problem with using a solid state replacement is that the heaters normally are connected to AC voltage but maybe you can rectify the AC with a simple bridge rectifier so you can use a solid state constant current circuit, this can be simple as no great accuracy is needed, a transistor, a few diodes and a few resistors should be enough.

Regards Hans
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Old 12th July 2004, 11:17 AM   #7
adalin is offline adalin  Sweden
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yeah I have all the spex on the tubes. Here are the list of tubes that is affected by the ballast tube

3x 6l6 0,9A each
1x 6sj7 0,3A
1x 6sn7 0,6A


that makes it a total of 3,6A

they are all 6,3v tubes


how do I calculate the voltagedrop?
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Old 12th July 2004, 07:48 PM   #8
dhaen is offline dhaen  Europe
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That's very odd. These cannot be wired in series.
Is there a mains transformer?
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Old 12th July 2004, 08:00 PM   #9
adalin is offline adalin  Sweden
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No...

When I took a closer look I realised that they wherent.

The 6L6 where wired in paralell and the only tube wired in serie with the ballast tube was the 6SJ7.

I was at work so I didnt have the thing in front of me... Never jump conclutions

But now I had time to really study the design.

There is a 12,6v winding going to the ballast tube and then to the 6sj7 so thats why there is a ballast tube so that the 6sj7 has the right heater voltage and current I think

But I dont understand why there is a ballast tube to begin with?

There is 6,3v windings at the main trafo..
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Old 13th July 2004, 03:05 AM   #10
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As I understand from your description the tube only have a few volts over it, in that case it is not a balast tube as those need in the order of 50 - 150V to work as intended. My guess is that it is a light bulb and it could be in the circuit in order to drop the heater voltage to the 6SJ7 tube.

BTW, the purpose of this "strange tube" in this circuit is not at all to slow the heater turn on, a balast or light bulb have very low resistance at turn on so the effect is opposite, the tube in series get higher voltage then it would get if it was connected directly to the heater winding.

It would help to understand the function if you can describe the circuit in more detail, can you post a circuit diagram?

Regards Hans
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