Aleph J illustrated build guide

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#4,543
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#4,545
I found myself trying to put together AJ on A30 board just for fun. I took many hours examining and cross referencing official A30 schematic with AJ schematic and think I have taken the necessary modifications so here is where the fun begins.

Because this is an experiment, I took old ZTX450/550 and J74 that I had removed from old projects and tested in $10 tester. Everything seems ok. IRFP240 are used as well.

I fired it up and see a nice 8.3V across R8 but only 3.43V across R7 and across the CCS according to this schematic:

Aleph J corr Nelson .jpg

No warm glow from the source resistors and mosfets yet. I have 2K pot in R7 and 100K pot in R27. With R27 at full resistance, I see a few millivolts across source resistors and since I have R27 installed with socket pin headers, once I left the pot out and turned it on and it started to warm up but I wasn't reading voltages and turned it off before I let out any magic smoke. Does it sound like everything is still working and anything I should check/adjust? Right now I have 1K resistor in R8. 2K pot in R7 initially set at 1K and I can adjust down any offset to 0.00mV easily.

Suggestions? Worst case I'll put small mosfets in place of jfets and call it A30.
 
#4,547
Zeners are noisy... C4 is there to couple the noise from the B2 base, to its "virtual ground return", which in this case, for Q2 -> is the V+ rail.

JFET's are sensitive to static discharge. You HAVE to use an antistatic wrist band correctly connected to a ground potential whilst handling the little buggers. My bet is that you damaged the JFET's... the output MOSFET's will not start conducting properly unless the voltage drop across R7 is at least 4.3V... so, the current through the Q1A is not sufficient at the moment to generate a required voltage drop; hence my diagnostics re: damaged JFET's.
 
#4,548
ghzgary said:
Thanks for that information! Yes, that would be 4.77A per rail on startup, more than I expected! I plan to do first power on at a lower voltage, something like +/- 15V then raise the voltage once everything looking ok (no smoke).
Click to expand...

Based on the voltage drop figures provided on the Aleph J schematics, across R8 and R7, plus a bit of voltage drop across Q2 (and a very little drop across Q1A), + and - 15 V DC at around 5 amps should be enough...but only just!

You can invest in a variac... and tone generator + an oscilloscope. Then with a tone generator outputting 2V at 1KHz sinewave, you can monitor the symmetry at the amplifier output; the amplified sinewave, while increasing the AC slowly... you also do not want to see any oscillations. The output sinewave should slowly increase as you crank the mains voltage - the same behaviour as increasing the volume. This ensures no explosions/unpleasantries 🙂, sanity and long and prosperous life.
 
#4,553
I realize the pinout is different from the small mosfets and the jfets and did a creative 'twist' to get the legs in the right spots but managed it without twisting legs around each other. Take the source leg and push it across to the opposite source (sources are tied together so it is ok), offset the G and D by 1 spot and do the same for the other side. It works and no ugly mangled jfets.
 
#4,556
Have you checked ANTEK website for the shipping costs to France? When I tried to ship ANTEK to Australia, I was horrified... shipping costs were insane.

Why not use Toroidy; they are based in Poland, fully potted and shielded. You can also get a very nice mounting plate that will make assembly task a breeze.
 
#4,557
after few hours of work , if you can put your fingers on Donut (be careful not to touch everything with exposed mains voltage !) and keep them for good , Donut is good


bit is normal ....... plenty isn't

say that 50C (closed case) is OK in my book ........ even if Donuts I'm using are much colder (1 of 250VA per channel)
 
#4,558
Extreme_Boky said:
Have you checked ANTEK website for the shipping costs to France? When I tried to ship ANTEK to Australia, I was horrified... shipping costs were insane.

Why not use Toroidy; they are based in Poland, fully potted and shielded. You can also get a very nice mounting plate that will make assembly task a breeze.
Click to expand...

I’m in the states and order from toroidy. I really like their transformers. Nothing with antek though; they make fine transformers too
 
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