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Burning Amp BA-3
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Old 4th April 2018, 09:33 PM   #2311
Zapped is offline Zapped
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Hi 6L6: re: posted test jigs for measuring Idss (page 161 in BA-3 thread). Is this jig also appropriate for testing JFET devices to go into an F5 amp? I mean with same dc test voltage, using a 9v battery. I have a regulated power supply, if there is any advantage to setting test voltage to a different value.

I have some Toshiba J74 and K170 devices I got from alweit (Alexander Weitzman, a guy in Israel) on ebay back in 2012; they are supposed to be BL grade and are ostensibly measured and matched, with Idss values noted on each pair of N, and each pair of P devices, but I would like to confirm those measurements are in the ballpark. (Alweit has a near perfect record on ebay, but I'd feel better seeing a reading on my own trusty old Beckman DMM.)

I also have some Linear Systems J74 and K170 devices I got from diyaudio a couple of years later, but they are A grade so I probably don't want to use them on the F5, unless they measure in the very high end of the range. Like over 6mA. Right?

Perhaps it is gilding the lily to worry about matching these input devices P to N, and channel to channel, but it seems as though a lot of bandwidth on the diyaudio pages has been devoted to just that! And we do like to get things right in this hobby.

BTW Is it true that I need not worry about matching the Vgs values of the output transistors in the F5? I got a tube of P and of N devices from Mouser or Digi-Key, so they are probably same batch.

Thank you for your help here, and in the past, especially for all your build guides in general! They inspire confidence and encourage diy projects around the globe.

"Zapped"
Larry Wright
formerly in Seattle area; now near Portland on the WA side.
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Old 4th April 2018, 11:19 PM   #2312
6L6 is offline 6L6  United States
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Burning Amp BA-3
Yes, the 9v and meter is fine for testing Idss of any jfets.

Alweit's transistors are genuine. If they are a BL pair feel free to slap them in the circuit without measurement, they will be what he said they were. That said, measure just to give it a try.

Yes, if the LS are on the high side that would be better for these amps, but it's not that big a deal.

The F5 output transistors need no matching.
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Old 4th April 2018, 11:31 PM   #2313
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Thank you, 6L6!
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Old 31st May 2018, 09:40 AM   #2314
generg is offline generg  Germany
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Burning Amp BA-3
Years later I have the impression that 30dB Nelson calculated as gain for the BA-3 FE, was simply for a load of 1k instead of 333R.

1k load is sometimes used in his commercial builds.

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Old 31st May 2018, 05:36 PM   #2315
Zen Mod is online now Zen Mod  Serbia
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Burning Amp BA-3
we all know that mistakes in his papers are result of multitasking

hard to track all designs in all iterations

anyway , that habit of his is good for our brains
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Old 31st May 2018, 10:18 PM   #2316
wintermute is offline wintermute  Australia
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Hmm I still haven't built my BA3 yet but I was thinking that 30db of gain seemed a bit high. I was thinking I would probably go for 20db which would match my 100W mosfet amp that drives my woofers

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Old 5th June 2018, 10:12 PM   #2317
PGTHOM is offline PGTHOM
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I completed construction of an Aleph J amplifier a couple of months ago and have been delighted with the result.
More recently I have considered constructing a Burning Amp consisting of an
input/gain stage w/o feedback coupled to a single ended follower output.
I have purchased the boards and components and have commenced construction.
However, I note that unlike the complementary follower version, the single ended version I have chosen doesn't appear to have any DC offset adjustment.


I was therefore wondering if anyone had constructed this version and can
advise what level of offset I could expect. I use these amps with full range
electrostatic loudspeakers where this is an important consideration.


Any advise on this would be appreciated.


Regards, Peter
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Old 30th July 2018, 05:12 AM   #2318
jwjarch is offline jwjarch  United States
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Any info on if/when boards might be available in the diyaudio store again?
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