I want to use a different tube that uses a 6.3V filament. I have a 12.6V supply but the reg is adjustable.
What resistor changes ie values do I need for the resistor divider network that is in there now. It has a 200R and a 2K. Schematic attached.
Much appreciated!
What resistor changes ie values do I need for the resistor divider network that is in there now. It has a 200R and a 2K. Schematic attached.
Much appreciated!
Attachments
The regulator is an LM317T (made by National Semiconductors and many others). You can calculate the resistors needed for a given output voltage by following the equation on pages 1 and 9 of the LM317 data sheet.
~Tom
Thanks Tom! My math is horrible but I give it a go since the formula is there. I have values in there as reference for calculation for 12.8V
WOW! The calculator is awesome. Looks like R2 or in my case R11 is 810R I get 6.3V
I don't think it will run too hot.
I don't think it will run too hot.
How much current?
If the tube is equivalent, then the current will be ~double that in the original circuit. The voltage dropped across the 317 will be 6.3 volts higher. So the dissipation in the 317 will be ~4 times the original.
Has it got a heatsink? 400% could be too much...
w
I was using a 5965 and will be moving to a tube with the following specs:
Uf = 6.3V, If = 350 mA uM = 25 Ia = 10.5 mA S = 6.8 mA/V Pa = 1.5 W
I have two filament supplies. One for each tube.
Uf = 6.3V, If = 350 mA uM = 25 Ia = 10.5 mA S = 6.8 mA/V Pa = 1.5 W
I have two filament supplies. One for each tube.
One last question. If I do run into heat issues with the reg can I go to a LM335T and have the same voltage divider resistor values?
You could put both heaters in series and run them off 12.6V. Rewire LM317 as CCS (3.57R reference resistor). Assuming your mystery tube is indirectly heated, you'll get the least noise, heaters will be protected by uneven or excessive heating during warm-up and your LM317 will run significantly colder than it would working as you intended for it.
That's a fascinating idea. I'm going to look into that.
Sorry to be mysterious on the tube. My friend swore me to secrecy because he might produce a unit based on that tube. Otherwise I would just have said the tube number.
Sorry to be mysterious on the tube. My friend swore me to secrecy because he might produce a unit based on that tube. Otherwise I would just have said the tube number.
Thanks again everyone! I realized when I looked at it the 2K was the trim pot so I changed the 200R resistor to 470R and it adjusts perfectly. I'll keep a temp gun handy to check the temp of the 317T to make sure it doesn't get too hot.
Yes, good idea to keep quiet about the tube number, once you let that cat out of the bag we'll all immediately know the application, toology, schematic, component values, physical layout, market segment and price positioning.
Does your friend work in the secret service by any chance?
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