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Old 14th October 2013, 10:00 PM   #21
flg is offline flg  United States
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I just figured that with Idss of 10ma on the JFETs you get 20ma through the 1k and 25Vds on the JFETs. You might have to loose 2-3Vds through the cascade JFETs so you might get 22Vout. No other changes, the simple way...
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Old 15th October 2013, 05:02 AM   #22
6L6 is offline 6L6  United States
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Ooooh!

Neato!

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Old 15th October 2013, 11:17 AM   #23
flg is offline flg  United States
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Well, I was somewhat mistaken above regarding "no other changes". You will need to adjust the Resistors driving the gate of the cascode transistors for a slightly higher voltage. Where N.P. has 18V you will need about 5 more Volts there. You can get that by lowering the Rs on each rail or raising the Rs in the middle. I don't have a pic of the schez or I'd give the ref des for the Rs. It should be simple to calculate and get close.
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Old 15th October 2013, 11:21 AM   #24
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A balanced version with cascaded FE feeding folded output is done using smd parts. Don't know how popular the balanced or smd would be for general use.
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Old 15th October 2013, 12:46 PM   #25
juma is online now juma  Serbia
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Quote:
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...You will need to adjust the Resistors driving the gate of the cascode transistors...
Exactly - current supply resistors need changing in that case too. With changes shown in the sch. below I got about 28V_peak of clean swing at the output (I didn't dare to go higher since the J74's Vds reached 29V). The current through R2/R11 (1K) was 16 mA (about 6mA through JFETs and 10mA through BJTs).
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Old 15th October 2013, 04:23 PM   #26
flg is offline flg  United States
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So Juma, what do you think of BJTs in the cascode position?. They are generally regarded, even by N.P. typically, as the better solution here. But, he chose to use more JFETs in this design?
Thx
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Old 15th October 2013, 05:46 PM   #27
massimo is offline massimo  Italy
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Juma, is BC547C for Q2 a typo? Did you mean BC550C ?
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Old 15th October 2013, 05:49 PM   #28
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But, he chose to use more JFETs in this design?
Keep in mind that this was an exercise in using LS parts exclusively.

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Old 15th October 2013, 05:57 PM   #29
CeeVee is offline CeeVee  Portugal
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...so there are better choices ? like Juma's ?
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Old 15th October 2013, 06:44 PM   #30
massimo is offline massimo  Italy
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...so there are better choices ? like Juma's ?
I dare say we should read between the lines.....
Or thruogh the emoticons
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