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Old 1st November 2012, 01:11 PM   #8421
atupi is offline atupi  Romania
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Quote:
Originally Posted by massimo View Post
But the ebay seller for FT-3 0.1uf lives in the same area with me so shipping free

Also, i have some Vishay Dale metalfilm available. Would be good to use those Dales or some carbons ?
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Old 1st November 2012, 06:04 PM   #8422
RCruz is offline RCruz  Switzerland
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Fighting a slight trouble with hum, I finally got rid of it with the help of some judicious GND arrangements.

It is incredible the difference it makes in overall presentation, detail, stage... superb.

One thing I must stress here... this new 58dB build is really silent.... At full blast I can hardly hear a soft hiss when I place my ears 10cm from the speakers.

Now I must get a propper metal case and start upgrading some components...
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Old 1st November 2012, 06:13 PM   #8423
Salas is online now Salas  Greece
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Success! You did not tell me, how much voltage across lower buffer JFET?
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Old 1st November 2012, 06:17 PM   #8424
Salas is online now Salas  Greece
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Quote:
Originally Posted by luxury54 View Post
dear Salas,
thanks for the link and for your efforts to modify the RIAA and publish the NAB EQ curve; I am lucky cause 7 1/2 IPS has the same EQ curve just like the 15 IPS that is published in the schematic, only the 30 IPS NAB curve is different to these
Yes, the Ampex papers were showing same repro amp curve for both 7 1/2 & 15 ips speeds.
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Old 1st November 2012, 06:18 PM   #8425
RCruz is offline RCruz  Switzerland
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11v... do you believe there might be some sonic benefits by increasing the drain resistor to 1800 ?
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Old 1st November 2012, 06:24 PM   #8426
Salas is online now Salas  Greece
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Not really, I took it to 1800 for when the BF245 went so to have ~22/2 across each buffer JFET for design elegance. That's in conjunction with the IDSS of the lower buffer JFET. If you will be rebuilding component quality and is handy try make the voltage 22V after the resistor with proper value judged in your build. If you will be able to discern anything better it can only be a plus. What it practically does is it equalizes the dissipation on the buffer JFETs.

P.S. Not drain resistor, RC filter resistor for buffer stage.
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Old 1st November 2012, 06:37 PM   #8427
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by Salas View Post
P.S. Not drain resistor, RC filter resistor for buffer stage.
You are right... this is a buffer, not a common source amp

I will take the 22v in consideration when I upgrade... thank you

In this case I should use 1k6 to drop 22v because Idss (calculated) is 7.95mA
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Last edited by RCruz; 1st November 2012 at 06:47 PM.
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Old 2nd November 2012, 02:21 PM   #8428
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Hi FET fans !!!

The postman got here from China today ( he looked exhausted ! )...
...with a 'test' of 10 Toshiba K170-BL...
...from eBay seller 'Polida'.

The JFET's were supplied loose, with straight-legs ( as per sellers photo )...
...and the 'typography' on the bodys was also the same 'style' as the eBay photo.

They have 'visible copper' at lead-out & no marking in rear-dimple.

It does look like they may be from several batches...
...as there are some different suffix-suffix's ( eg. after K170-BL ( factory run code )).

They are all within the Toshiba spec. for BL ( blue ) devices ( 6-12mA ).

Here's what I got...

10.76
10.52
10.36
10.35
10.21
9.36
8.45
7.84
7.23
6.70

All tested with simple new 9 Volt battery & good-meter...
...left to 'settle' for about 2 mins each.

Can't complain I suppose...
...any thoughts or comments, anyone ?

Cheers

Si.
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Old 2nd November 2012, 03:52 PM   #8429
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Any other way of testing them? You could build a simple circuit to acess the sound.
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Old 2nd November 2012, 04:45 PM   #8430
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I am building a simple circuit to access the sound...

...'Simplistic NJFET RIAA'
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