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Old 26th February 2013, 12:18 AM   #261
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by buzzforb View Post
Taking it further would mean matching for Yfs, Ciss, and leakage. He was simply trying to reiterate the practical use of pot at R7.
we were talking strictly about DC condition ........where only leakage maybeeee can take some influence

anything else is story for Back to the Future part II , III and IV - armed with AP or any surrogate
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Old 26th February 2013, 12:31 AM   #262
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Buzzford and Zen Mod,

Thank you for your feedback. As I mentioned in a previous post, since I still have to test the second board, I'll add the R7 cermet before mounting it to the heat sink. This way I can make the adjustments to see how low I can get the DC offset and also determine if anything else is needed. I am not disputing any of the advice given.
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Old 26th February 2013, 12:37 AM   #263
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no harm feelings , disputing or not

just trying to help you to realize what's important and what is , to put it mildly - mumbojumbo

then
you can make your own tests and have your own conclusions
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Old 26th February 2013, 01:07 AM   #264
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Quote:
Originally Posted by Zen Mod View Post
we were talking strictly about DC condition ........where only leakage maybeeee can take some influence

anything else is story for Back to the Future part II , III and IV - armed with AP or any surrogate
Yup. In my stupidity, i missed that.
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Old 26th February 2013, 04:15 AM   #265
henryve is offline henryve  South Africa
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grimberg
I have added C7. Since it is a standard bypass capacitor I assume that it is the same as C6. Please correct me if I am wrong. I might have to give an exact value for each here for those with not much experience. Suggestions for the values of C6 and C7 please.

All
Please verify the values of the pots that I suggested, especially R27 and the resistors around it.

BOM now at revision C already due to late changes/updates.
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File Type: pdf BOM-Aleph-J-UMS.pdf (448.7 KB, 2001 views)
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Old 26th February 2013, 05:35 AM   #266
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Henry,

This is the bypass capacitor I used for both C6 and C7.

MKP2D031001F00JSSD WIMA | Mouser

In the original Aleph J schematic both R7 and R8 have the same 1K value. I suggest using 2K multi-turn trimmers for both.
For R27 the board is configured for one fixed resistor in series with a trimmer resistor. I suggest using a 56K2 resistor + 20K multi-turn trimmer.
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Old 26th February 2013, 02:43 PM   #267
henryve is offline henryve  South Africa
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grimberg

I see Mouser currently has no stock of that capacitor, and are only getting stock in during April. I have updated my BOM to use your version as I made a mistake in the one I listed. I see that the one I listed has a lead spacing of 10mm and not 5mm.
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Old 26th February 2013, 03:51 PM   #268
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Quote:
Originally Posted by grimberg View Post
JFETs are graded by IDSS and grouped in 3 ranges identified as Green, Blue and Violet.
So that's what G, BL and V mean! It always seemed arbitrary, and I never thought it was a color code!!!


Quote:
In the channel on the photo the JFETs have IDSS 9.31mV and 9.36mV. In my view, "tightly" matched.
That is more than good enough.


Quote:
I made a commitment to build the boards quickly and had the parts in hand for a "standard" build, as the boards I intended to use do not have room for trimpots. I made good on my commitment to 6L6. Now, with the help of Mighty ZM and other members, I'll try to make the amplifier as close to "perfect" as possible.
Your (very) fast construction and testing is greatly appreciated. The PCB dimension issues and pad sizing is exactly what needed to be found by this process. Thanks!

Your photos look great, BTW.

I never meant for the 'standard' build to be without the pot on R7... That one seems to be necessary, while the rest of the pots are there to adjust it to the last degree of perfection or just to play around.

Please do whatever adjustments you wish to get the amp all tuned up and measuring the way you expect -- I am quite eager to see what it takes to get it perfect.
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Old 26th February 2013, 05:42 PM   #269
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Quote:
Originally Posted by henryve View Post
grimberg

I see Mouser currently has no stock of that capacitor, and are only getting stock in during April. I have updated my BOM to use your version as I made a mistake in the one I listed. I see that the one I listed has a lead spacing of 10mm and not 5mm.
Henry,

These will all fit and are currently in stock. Their values range between 100nF and 150nF, and they differ mostly in voltage and tolerance. Any of these can be used in C6 and C7 positions.

MKP1837410161F
MKP2F031501K00JSSD
MKP2D031501H00JSSD
MKP2D031001F00KSSD
MKP2-.1/250/5
MKP2-0.1/250/5X2
MKP2D031501H00KC00
MKP2D031001F00JSSD

Last edited by grimberg; 26th February 2013 at 05:45 PM. Reason: Corrected value range
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Old 26th February 2013, 05:50 PM   #270
henryve is offline henryve  South Africa
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Thanks. I will add to BOM as alternatives.
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