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Old 19th December 2012, 02:44 PM   #3651
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Which board is better??

I would think the new board with the brighter LED....yes??
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Old 19th December 2012, 06:24 PM   #3652
Salas is offline Salas  Greece
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Its no better just more current in the Jfet useful if needed to go high B+. Could be just an led with more lumens, because for same Vo, there is same current in the Vref. To match Jfets for Idss is simple http://www.diamondstar.de/transistor_matching_jfet.html
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Old 19th December 2012, 11:58 PM   #3653
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I will try the pair first....and at the same time try get more Jfet to match...tks
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Old 20th December 2012, 12:51 AM   #3654
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1) do I need to use Jfet with higher Idss for higher possible B+??

2) if I turn up TP higher, say to 50mA, I can get higher B+...is it OK to do so??
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Old 21st December 2012, 07:29 AM   #3655
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Salas....I connected the two SSHV2 boards to the PSU...and the pair of tubes....VT-25A loaded by a pair of //12K (=5K) resistors.....

Funny thing happened....with 288V into the two boards....I can get 288V out...and quite stable as far as I can tell....but when I take the output down to 278V...they become less stable until say 268V....

Can I let them stay at 288 in and 288 out??
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Old 21st December 2012, 07:32 AM   #3656
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I have not matched and changed the two 2sk117
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Old 21st December 2012, 11:35 AM   #3657
Salas is offline Salas  Greece
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What you describe sounds like you move them about the non regulation zone with marginal spare current. They can regulate very close to Vin, but at Vi=Vo they just follow input, still when you go enough lower Vo the tubes bias for less current and they can control them at given TP CCS having some spare for themselves finally. That is why you can fix for more Vo with higher TP measurement.
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Old 21st December 2012, 11:55 AM   #3658
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After all, it is not like to be at the end of the world...!! (a few more hours around the world will confirm....haha..

OK....in layman terms....I would like to bias the tube at close to 8-9mA each (the V across the 6K load resistor is now at 40-50V) ....so should I set the TP at 30mA for each board?? is 3omA enough ?? what is the minimum mA??

I do not worry about the B+ ( the board output)....as long as I can set the voltage across the load resistor to be within 40-60V and have stability.....

My B+ transformer is rated at 125mA (a Canadian transformer)....my //choke is rated at 40mA each.....should I change my PSU when using 2 boards??

What should I do to go forward...what mA level to set TP at to try again....

Merry X'mas,

King
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Old 21st December 2012, 11:59 AM   #3659
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The weakest link in my PSU in term of current is the //choke....which is 40 + 40 mA = 80mA...correct??

So should I set each TP at 40mA to start again??

Cheers,

King
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Old 21st December 2012, 12:05 PM   #3660
Salas is offline Salas  Greece
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Yes. Merry Xmas 2U2.
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