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Old 1st March 2013, 07:15 PM   #11
RuiR is offline RuiR  Portugal
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Originally Posted by rknize View Post
Are you using FETs in place of the CCS? If the CCS is doing it's job, the voltage will vary as the CCS maintains a constant current. What is the voltage *across* R13/23 and R14/24?
I already taken them out I had the time and done it because i will be busier.
*across*? It had about 325v after R14/R24 and the same voltage before R13 and (i can't be certain) after R13

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Originally Posted by rknize View Post
Apart from that, yes it does sound like a thermal issue. You are not using thermal paste? Have you adjusted the resistor values on your FETs so that you get the desired ~9mA of current through the tube?
I did use thermal in the first set, the one that take longer.
yes i did use 330Oh resistors with the IXCP10M45S - about 9.4mA and 185Oh when i used the DN2540 - ~10mA

Thank you Russ, i learned a lot from your posts when i was building it 1 year ago. I implemented the variable resistor switch
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Old 1st March 2013, 07:39 PM   #12
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By across, I mean putting a probe on each side of the resistor and measuring the voltage across it. That will tell you what the current is and how it may be drifting. I assume you were measuring relative to ground?

Others have used the DN2540 with good results. Maybe it is oscillating?
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Old 2nd March 2013, 09:01 AM   #13
RuiR is offline RuiR  Portugal
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Originally Posted by rknize View Post
By across, I mean putting a probe on each side of the resistor and measuring the voltage across it. That will tell you what the current is and how it may be drifting. I assume you were measuring relative to ground?

Others have used the DN2540 with good results. Maybe it is oscillating?
Thank you.

Yes, i measure to the ground, newbie but not that much

The first set i used was DN2540's

This is how i assemble them:

Click the image to open in full size.

Click the image to open in full size.


The two nuts are to gain hight so it can be pressed against the board
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Old 13th March 2013, 03:29 PM   #14
RuiR is offline RuiR  Portugal
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Exclamation Lost.. need help please

Hi

I lost count the times i already dismantle this thing trying to spot why it doesn't work

I'm ending with a voltage after R14/R24 equal at B+ in R4, ~450/460VDC.

Before R13 and R14 i'm getting 12VDC at one side and 2VDC in the other With no voltage or a residual only at R10/R20

I'm starting to despair and i might pick a shovel and bury it

With the mosfets changed i managed to lift their tracks, i replaced them with wire and the circuitis fine.... i looked so many times to them and i can't see any problem there

Please any thought? Even the the most odd one is welcome
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Old 13th March 2013, 04:25 PM   #15
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How did you insert MOSFET in the specified schematic? I can't see MOSFET's in that circuit.
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Old 13th March 2013, 04:27 PM   #16
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Maybe bigger heatsinks from an old computer CPU & computer 12V fans run on a lower voltage like 6-8V for quiet running would help as it's probably hot where you are also.
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Old 13th March 2013, 05:00 PM   #17
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Ehhhhhh, too much for a low current sink!
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Old 13th March 2013, 06:44 PM   #18
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Quote:
Originally Posted by Osvaldo de Banfield View Post
How did you insert MOSFET in the specified schematic? I can't see MOSFET's in that circuit.
It's on the left of the schematic Simple SE schematic

Anode to R14/R24
Gate to R19/R29
Kathode to R13/R23


Thank you
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Old 13th March 2013, 06:48 PM   #19
RuiR is offline RuiR  Portugal
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Originally Posted by rmyauck View Post
Maybe bigger heatsinks from an old computer CPU & computer 12V fans run on a lower voltage like 6-8V for quiet running would help as it's probably hot where you are also.
It's a proven design with others running without fan aid. I'm doing something wrong or something is malfunctioning

Thank you
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Old 13th March 2013, 07:22 PM   #20
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This wiring is true for constant current sources (like LM336) but isn't true for MOSFET's. You will need to rewire your circuit to use P channel MOSFET's as CCS or BJT's. You need to generate a voltage of about 3-4V between gate and source (depending of the polarity of the MOS transistor) to turn it on (Class A biased), and then adjust source resistor to get drain current you need. Power in it will be directly I * E across the mos, then multiply it by the thermal resistance from die to air, and you will get temperature rise in the MOS without the heatsink. If this rise is too high, use a proper heatsink needed to reduce temperature to normal (< 70 deg Celsius) value.

But, why not to use the other half of the 'AT7 as a SRPP?
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