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Aleph J illustrated build guide
Aleph J illustrated build guide
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Old 27th December 2017, 12:39 PM   #2361
xrk971 is online now xrk971  United States
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Aleph J illustrated build guide
Wow, those sound like they were pro-matched to the highest standard. About same price as DIYA store quads but matched to some insane high standard.
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Old 27th December 2017, 04:49 PM   #2362
2 picoDumbs is offline 2 picoDumbs  Australia
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Hahaha
Yes nicely matched.
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Old 27th December 2017, 06:22 PM   #2363
pchw is offline pchw  United States
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Aleph J illustrated build guide
Only with enough quantity of parts :-)

The GR is at $2 a piece for the time being. One possible "alternative" is to buy enough GR to match them in pairs to make the BL, like 2 x 3.5mA GR's in parallel => one BL at 7.XX mA at $4, not too bad. The remaining unmatched GR's ain't waste either.

I am going to order some and will report how the above scheme plays out :-)
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Old 27th December 2017, 07:24 PM   #2364
Russellc is offline Russellc  United States
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Aleph J illustrated build guide
Quote:
Originally Posted by 6L6 View Post
Alwieit is the Israel fellow, his are real, but yes, I believe he is out of BL as well. <snip>
Not that expensive, listed in HK dollars. Last I bought were less than what store asks...May be price has gone up?

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Old 27th December 2017, 08:11 PM   #2365
EUVL is offline EUVL  Europe
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> to match them in pairs to make the BL

In doing so you also doubled the capacitances.


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Old 27th December 2017, 08:35 PM   #2366
pchw is offline pchw  United States
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Aleph J illustrated build guide
Totally understood. I am hoping some will land in the 6mA range, then they can mate to my low idss 2SK170BL without the penalty. Only a few of my limited 2SJ74BL's are in this low idss range, so I have quite a few 2SK170BL's that are in this range with partner.

To me it is worth a try as long as the jfet's are real which always beat the fakes regardless. It is a gamble afterall.

Edit: For the purpose of AJ, as long as the IDSS is above 5mA, I believe they can be used. The CCS in the tail pumps about 10mA.
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Last edited by pchw; 27th December 2017 at 08:41 PM.
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Old 27th December 2017, 09:00 PM   #2367
2 picoDumbs is offline 2 picoDumbs  Australia
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Change input and feedback resistors from 22.1k/221k to 10k/100k if using parallel pairs.
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Old 28th December 2017, 05:44 AM   #2368
indra1 is offline indra1  Indonesia
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Originally Posted by EUVL View Post
. . . . In doing so you also doubled the capacitances.
. . . .
Also almost double Yfs. When applied in Aleph J would extend top end similar to the J2?
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Old 3rd January 2018, 01:00 AM   #2369
Eslheadphone is offline Eslheadphone  United States
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I built a jig for matching the IRFP240 MOSFETS. I simply used the constant current source circuit from the amplifier and measured the voltage across the Gate and Source. I ran the power supply on a Variac and monitored the VGS for about 5 minutes and wrote the VGS on the FET. Out of 24 FETs I came up with 8 pairs all matched within 2 or 3 mv of each other. It may be time consuming but it works well. I am thinking that a larger heatsink with a large power supply could do multiple fets as all the drain leads could be common. No insulators would be needed.
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Old 3rd January 2018, 06:52 PM   #2370
Eric is offline Eric  United States
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Aleph J illustrated build guide
If you order in multiples of 25 (a full tube), you're very likely to get lots of matched pairs/quads/etc. I matched mine with a similar jig, but without the heatsink - they were just in free air. I used 20v, 0.75A for about 45 seconds - any more and they get too hot to handle. This was enough time to obtain closely matched pairs for my big Aleph-X amps. For these mosfets, most people want to match them at the specific voltage and bias that they'll see in the completed amp, but it seems that simply matching them at any realistic voltage and bias level will provide good results for other voltages and bias levels as well.
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