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Old 11th January 2011, 05:37 PM   #11
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Default FET

Hi Rich:

I have 2SK389, email me your mailing address and and I will send it to you.

Art
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Old 11th January 2011, 05:53 PM   #12
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by timetec View Post
..
I need a TO18 heatsink if anyone has one - I just can't seem to get one here in the UK and Digikey want 12.50 for shipping one from the USA, which I simply can't justify, for something that weighs no more than 10grams !!
I have a circuit running on a breadboard right now, been running now for 72 hours. I improvised a small heat sink with a strip of aluminum cut from a soda can and held in by an alligator clip. Seems to be working well. It cools a part that used to almost burn my finger to one that is just barely warm. The trick is getting good contact.

I have also seen a brass washer used. If the transisor is in a metal can you can make a washer fit by filing out the central hole or adapt a section of copper tube.
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Old 11th January 2011, 06:02 PM   #13
timetec is offline timetec  United Kingdom
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Many thanks for the offer Art, that's really very kind of you

I've just had a look at the Toshiba data sheet for the 2SK389. Not sure if this would work reliably up to 2Mhz been designed as an audio device, but I may be wrong - the IMF3958 / upa71A components however, are classed as an RF differential dual-fets. My other concern, although 'not the end of the world' so to speak, is the pin spacing / layout which could be quite fiddly and involve adding sleeved extensions to the closely spaced legs - what do you think ?

Richard
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Old 12th January 2011, 02:24 AM   #14
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Hi Rich:

Q105 is configured as a follower/buffer. The lower fet is a constant current source.

What if you flip the device and use the section that is not leaky, and use any jfet as a ccs?

Just an idea.

Art
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Old 12th January 2011, 09:58 AM   #15
cliffyk is offline cliffyk  United States
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There are a number of listings on eBay for the 2N3958, a direct replacement; also here's a UK source in Surrey.

The dual package was selected for temperature tracking/stability reasons, using separate devices is not recommended.
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Old 14th March 2011, 09:05 AM   #16
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Default Leader Lfg 1300s schematics

Hello to you all. I'm looking for some time, for didactic reasons (working in a technical institute) the wiring diagrams of the function generator Leader LFG 1300s. I have seen those kindly provided by timetec, but would appear to partially incorrect: the capacitor C103 has both terminals on the ground, and has continually the Ic106 pin 3 shorted to ground by switch S101.
In particular, I'm looking at the circuit on the low-frequency (hz 0,1-1-10).
The diagram shown in pic 8 seems to be overhauled.
Can you help?
Thanks in advance and greetings to you all.
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Old 30th May 2012, 11:10 PM   #17
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updating an old thread, I know.

I just bought one of these on ebay and it seems brand new or nearly new. the bnc fiber caps were still all (no one who *uses* the gear leaves bnc caps on, lol).

I wonder if I should upgrade things inside, just for good measure, seeing that its an old-stock item? caps? op-amps?

very pleased with the usability of this FG. nice large dial, marked up to 2.0 for obvious audio use, intelligent layout of controls. very well thought out user interface, which is what drew me to buy this one.

I can't stand to leave 741's inside, though surely I'd get better perf with something more modern? lower noise and cleaner waveforms, perhaps, as a result?
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Old 19th June 2012, 06:43 AM   #18
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Well done. Learn a lot from this.
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