for Shannon: a CCS for ST35?

for the DIY ST35, the Dynakit and every other PP EL84

Postby mesherm » Wed Jul 23, 2008 2:31 pm

Image

Here is an example of a 3-terminal regulator I used as a constant current sink in a 6V6 amp I built. Its fairly simple to build. I configured mine with a trim pot since I hadn't settled on a idle current yet and I wanted to experiment. Thats also the reason for the 10 ohm resistor in the cathode circuit, so I could measure the idle current. Once the current is set it doesn't matter what 6V6 you put in. The current always stays the same. I used the TL783 rather than LM317 because the TL783 has a 125 volt rating, uses MOS output transistors, and has a lot of built in safety features. The TL783 DOES have to be heat sinked however.
The TL783 datasheets have the formulas for determining what resistor gives what current when the regulator is configured in the constant current mode.
Mike's N-1 Rule: When looking for N number of components to finish a job, you have a 95% chance of only finding N-1 of them.
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Postby Shannon Parks » Thu Jul 24, 2008 6:12 am

DerekVa wrote:
separks wrote:Is this the LM317 mod? I need to see if I wrote anything down. In the meaning, search the forums for LM317.


Probably. Basically I need to know how (a) you build one (b) you hook one up and (c) the reasons they work.

Unfortunately, everything I've been able to find out on the interweb assumes you know (b) and (c). I don't.

-D


Still researching this one. Of <course> I didn't right anything down. Yellow_Light_Colorz_PDT_09 Let me review my old posts and look at the test data to give you an idea of output power. But basically you lose the cathode resistors and pot (the 10R remains I think), and plug in the LM317 into a Rev D board with its current set resistor (~35mA). The current sink does the work. Checkout the datasheet.
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Postby EWBrown » Thu Jul 24, 2008 2:16 pm

I've posted in the past about using LM317s and 7805s, etc as cathode CCS for the EL84s, it works, but it's best if the tube is running full Class A rather than AB1 or AB2. For an LM317, use 36 ohms for 34 mA or 33 ohms for 39 mA, the idea is to get a 1.25VDC delta between output and adjust pins, the "input" pin goes to the cathode, and teh "adjust (not output) pin goes to ground. Bypass as usual from cathode / input to ground with 100 to 470 uF, 35VDC caps.

For 7805s, use as a simple 5V regulator, input to EL84 cathode, then load teh 5V output with 150-140 ohms, this makes the device regulate at 33.3 or 35.2 mA The exact number fora 7805 and 35 mA is 142.857 ohms, but then we don't have to be "mathematically anal" like Mister Spock, here, within 5% is more than good enough...

The Rev D board has the pads for this, but it isn't (as far as I know) documented in the instructions.

I've modified a "D" board for PP 6S4As, running around 25 mA @ 325VDC B+, but this and all other major projects are on hold until the move to NC is fully completed.

It's raining hard outside and the Gray Tree Frogs are giving me a multi-channel "serenade" Yellow_Light_Colorz_PDT_03 Yellow_Light_Colorz_PDT_04 :o

ed B in NH / NC / NH / NC........
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