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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Thanks Dave. (No 5.) posted by Bas Horneman on July 3, 2002 at 09:33:05:
OK... im not an EE either :-) but getting the drawing right is the first step to proper assembly.you still need a DC blocking cap on the primary of the IT... otherwise the DCR will provide a short to ground... imagine 150V on the plate of the 6BX7 and a 500 ohm dcr of your IT, without a cap to block that DC to ground the trannie will try to pass 300ma....
onto the bias supply, follow the DC current loop, the output of the filter forms a series circuit feeding the resistor, IT secondary, then the grid of the tube... it is completed by the grid to ground resistance which is extrememly high, so virtually no currnet will flow... no current means no voltage drop across your resistor, so you will have nearly the full B+ (inverse because its a negative supply) on the grid.
you have two options (well many more)
you could place two resistors in series to ground and size them properly so the junction of the two act as a voltage divider sized to give you the proper bias voltage... say the supply is -500V... if you put a 100K and a 10K resistor in series to ground with the 10K grounded, the 500V will see 110K to ground. that will draw 4.5ma... 4.5ma across the 100K resistor will give you 450V and the remaining 50V will be across the 10K resistor so this will provide you with 50V to feed into the bottom of the IT, since no current will flow, that will be your bias.
you can play with a cap from across the 10K resistor to see if it helps.
its all about learning to use ohms law... that is the first step in sucessful design.
dave
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Follow Ups
- Re: Thanks Dave. (No 5.) - dave slagle 10:11:18 07/03/02 (1)
- Re-read your post.. - Bas Horneman 08:21:04 07/05/02 (0)
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