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Old 3rd December 2011, 01:37 PM   #21
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FAHNSTOCK CLIPS! Love it!
One of my other hobbies is building crystal radio sets.
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Old 3rd December 2011, 02:50 PM   #22
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For those without distortion analyzers, I'll soon post a table of operating point values for different loads assuming a 50-55V supply. Give me a week or so. We'll also play with the number of bulbs for good measure.

Thanks a lot ... looking forward to the table...
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Old 4th December 2011, 04:24 PM   #23
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If you build Figure 11, with a 16 Ohm speaker, 1W THD goes to around .5%.

With the adjustable version (Figure 10) with a 50V volt supply, I found a nice sweet spot at around Id=2.42A and Vds=19.9V. There, the 1W THD was .069%, which is pretty nice. You'll get more gain, but less power, so your 16 Ohm speaker needs to be pretty efficient.

Now, the point of minimum distortion won't necessarily be your favorite spot. You may want to play with the setting a bit and see what you like best.

As for impedances much lower than 8 Ohms, I wouldn't use this little amp with 4 Ohm speakers.
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Old 4th December 2011, 04:50 PM   #24
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sorry for my dumb question , but i have never build a transistor amp just single ended tube amp , so for me i figure the Fig9 will be more appropriate . so what is the best Drain ( anode?) voltage for fig9 ?

is the 10uf input cap is obligatory?

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Old 4th December 2011, 05:21 PM   #25
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You must mean Figure 10?

There's a table of possible supply values and operating points a little further down the page. Somewhere between 45-55V is good.

The cap? I'd just leave it in, but If you're absolutely certain your preamp output is cap-coupled, you could eliminate the cap.
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Old 4th December 2011, 05:22 PM   #26
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juanitox,

Fig9 is just a test setup. Fig11 is probably the easiest to build because it does not require a separate bias supply or the input cap.

I am interested in how Fig11 would behave with R3 bypassed with a cap. I suspect that you get much of the advantage of Fig10, but without the added complexity of the external bias supply.
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Old 4th December 2011, 05:30 PM   #27
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juanitox,

Fig11 is probably the easiest to build because it does not require a separate bias supply.
I agree, Figure 11 is an easier first time build. Grade KD-33 is needed for that one. Other grades have a different Vgs.

About that input cap: Given enough leakage current, the input will be offset from zero, so eliminating the input cap isn't a slam dunk. Having tested only four parts and and not knowing what to expect from the universe of 2SK82s, I put one in the drawing.

Last edited by Michael Rothacher; 4th December 2011 at 05:40 PM.
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Old 4th December 2011, 06:36 PM   #28
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damned i have bought KE33 grade is it mistake?
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Old 4th December 2011, 06:39 PM   #29
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Not necessarily. You could just build Figure 10 instead.

Have a look at the complete schematic I posted at the very beginning of this thread for more info.

L'Amp: A simple SIT Amp

Last edited by Michael Rothacher; 4th December 2011 at 06:44 PM.
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Old 4th December 2011, 06:49 PM   #30
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Hi Michael,

I am curious to know more about the effect of leakage current in this circuit. Specifically, what sort of non-zero voltage would be expected at higher leakage numbers?

Also, any thoughts on cap bypass for the source resistor?

I would like to try the circuit as drawn below.
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