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Old 4th April 2012, 07:42 PM   #121
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by Tea-Bag View Post
Isn't the input capacitance too high on these?
seems like higher capacitance comes naturally with the higher power rating and transconductance

I dont think there is any way around it
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Old 4th April 2012, 10:25 PM   #122
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Quote:
Originally Posted by lhquam View Post
I bought 25 each of FQA36P15 and FQA28N15 because of the apparent unavailability of FQA19N20c and FQA12P20.

Where can one obtain FQA19N20c and FQA12P20?
I have source for FQA19N20 they sell minimum of 1000 pieces so no go for me there
If one has the cash to go for it PM.
FQA19N20C is one different kind of beast with more capacitance and more power then there is the FQA19N20 L even more power and again more capacitance.

I use FQP19N20, which is closer match(current wise) for FQA12P20 but has TO220 pack
Having bought 100 each I can spare a few so Pm
They have been running since last August on MY F5.

I quite like the idea to use the 36 and 28 as you mention I am not shure how they perform and my Knolledge is limited so it will have to be a build and see thing the gain of those 2 is quite interesting so try them and report back.

I have seen post about potential buy of the original pair 19 / 12 will need to search for that
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Old 4th April 2012, 10:55 PM   #123
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For me it is interesting to look at the capacitance and transfer curves of the 12P20 and 19n20C. You could use a transparency and lay them on top of each other and you have jsut about an exact match for same conditions. Now try with 19n20 and you see differences beginning to appear. L version is even worse. Could be wrong, just interesting
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Old 4th April 2012, 11:22 PM   #124
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Quote:
Originally Posted by buzzforb View Post
For me it is interesting to look at the capacitance and transfer curves ... Could be wrong, just interesting
You could be right and just posted sometink I did not see.

Tanks that sound realy interesting.

And buzzforb link to Sign Up Sheet is the one I was going to search for

Last edited by Bksabath; 4th April 2012 at 11:26 PM.
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Old 5th April 2012, 05:00 AM   #125
pchw is offline pchw  United States
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Quote:
Originally Posted by lhquam View Post
I bought 25 each of FQA36P15 and FQA28N15 because of the apparent unavailability of FQA19N20c and FQA12P20.

Where can one obtain FQA19N20c and FQA12P20?
I have some surplus matched FQA19N20C and FQA12P20. What kind of matched (N-N, P-P) sets are you looking for? You can PM me if you are interested in.

Thanks,
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Old 5th April 2012, 11:40 AM   #126
Tea-Bag is offline Tea-Bag  United States
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Working on a dual purpose board that can do FQA or FQP.
With proper mounting like BKsabath, one should be fine with the smaller package units.
They should promise in one direction, they are still avail via normal distribution.
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Old 5th April 2012, 04:29 PM   #127
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I have a question about V3,The R25=10K,but the R26=47.5K,why? it it wrong?
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Old 9th April 2012, 01:30 AM   #128
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Hi all!

How can I check if my jfets are original or not?

Thanks
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Old 9th April 2012, 02:08 AM   #129
Rush is offline Rush  United States
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Quote:
Originally Posted by lilinyi View Post
I have a question about V3,The R25=10K,but the R26=47.5K,why? it it wrong?
That does look suspicious. They should both be the same. This effects V2 as well if you are cascoding the input. My guess is the 10k is right, but it could depend on the rail voltage. I am running 32 volts and need to know for sure.

I sure hope someone smarter than me pipes up.

Rush
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Old 9th April 2012, 07:24 AM   #130
Itsmee is offline Itsmee  England
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R26 should be 10K, assuming 60V supply rails

-60V
________ x R28 = -19.32V the correct voltage reference for the cascode transistor
R26+R28
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