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Old 23rd January 2013, 05:16 PM   #1151
ittien is offline ittien  Viet Nam
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Quote:
Originally Posted by AndrewT View Post
25kHz is +-0.6dB ref 3.342Vac @ 1kHz
40kHz is ~ -1.3dB ref 1kHz.
Not great.
But, did you check your input signal?
Is it constant at those spot frequencies?
Or does it too vary as you sweep the frequency?
AndrewT: ofcourse the input constant as every frequency, i used it to do measured amp very often.
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Old 23rd January 2013, 05:25 PM   #1152
sangram is offline sangram  India
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Quote:
Originally Posted by AndrewT View Post
No.
You still have not got how tolerance works.
1.01||1.01 - .505
.99||.99 - .495

Diff=.01

= 1% of 1 ohm.

What am I doing wrong?
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Old 23rd January 2013, 08:08 PM   #1153
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Ittien,
perhaps this might help
F5 turbo problems
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Old 23rd January 2013, 08:57 PM   #1154
Zen Mod is offline Zen Mod  Serbia
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ittien - are you having one pair of input Jfets ?

if possible , try to double them (piggyback , if there is no place on board)

prior to that - reset output bias to 0

then inform us
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Old 23rd January 2013, 11:35 PM   #1155
ittien is offline ittien  Viet Nam
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@ZM: I still have JFet that matched by seller from Japan.
With this F5T, I already tried try to replace all of other components. but not try another JFET. all of other changed can make the sound better, but F5T always get poor dynamic range and narrow bandwidth. So what the buzzford said the bad JFET also make sense. that's the only one that i can not change so far. i tried to bias from low (200mV) to high(450mV, used fan), does not help.
attached is some images of my JFET, i have both V and BL, see if you can point out it is the bad.
DSC_5042.JPGDSC_5043.JPGDSC_5044.JPG

I will tried to double them tonight and will let you know.
thanks
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Old 24th January 2013, 03:21 PM   #1156
ittien is offline ittien  Viet Nam
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Zen Mod: it so strange, after double JFET, although i set bias to 0, power on and can not bias any more for N channel, P channel is fine. remove all FET and Diode to check is all of N are dead, P channel is fine, all diode fine.

Check Jfet section only, all bias work fine, i can bias for more than 4V, nothing wrong with JFet section. mount new output FET and diode, check everything by ohm meter, all are good. 5K trim port both well, set them to minimum value. power on, and can not bias on N channel again. trim port 5K on N channel can not bias for more than 2V. then check all FET on N channel dead again. .
I don't have any N channel FET any more to play with.
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Old 24th January 2013, 03:32 PM   #1157
ittien is offline ittien  Viet Nam
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Then i maybe not the lucky man, buy lot of jfets that are not good. Read in this forum, i saw lot of people buy a kit, and make it work without any problem. reviewed the sound and bandwidth very good. but me, and other DIYes in my country, no-one can make F5T work properly. sound bad and very easy to get fired at night or day, I also make F5 standard version, sound also not good either. we all buy jfet together from 1 seller. this should be the point.

Last edited by Variac; 25th January 2013 at 06:03 AM.
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Old 24th January 2013, 03:33 PM   #1158
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ittien, you have PM
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Old 25th January 2013, 06:58 PM   #1159
Renron is offline Renron  United States
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Just tried to order a TX 25V 1000VA from Antek, their website say EVERY TX in stock; availability is 0 ???
How could they be out of EVERY TX ? The phone number just rings and says no one is answering and then disconnects. Any Idea whats up? Last I heard they were training new employees....... sorta contradicts what their website and phone system is doing.
Ron
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Old 25th January 2013, 06:59 PM   #1160
PKI is offline PKI  United States
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Ron,
Antek transformers Down?
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