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Old 5th June 2021, 12:55 PM   #451
adason is offline adason  United States
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Quote:
Originally Posted by analog_sa View Post
Low Ft?

I think it is a bad idea to run it as CE. As EF you will get lower distortion, better HF response and higher input impedance. If you do need voltage gain add another stage in front.
analog_sa, the emitter follower is certainly a good idea, and it works, I moved the output from collector to emitter and hum is gone
so is gain, but that was expected

i do have plenty of small balancing transformers, 600:10k, I will put it on the input, should boost the signal enough for headphones

thanks
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Bias is voltage Vgs, and controls drain current Id

Last edited by adason; 5th June 2021 at 12:59 PM.
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Old 5th June 2021, 02:21 PM   #452
adason is offline adason  United States
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just measured 0.141% distortion at -10dB level
not bad
I can see second harmonic ~-60dB, and third ~ -80 to -90dB, depending on the current I set with trimmers
I can set anywhere between 40 to 100mA comfortably, and increasing the current decrease the 3rd harmonic mainly
I am thinking of making trimmers into pots and put them on the front, so I can adjust current based on headphones impedance and desired harmonic spectrum

I was wrong, hum is gone in headphones, but on the measurements, still significant left
need to work on filtering the bias setting, likely...

and hf rollof is still there
but it sounds awesome
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Bias is voltage Vgs, and controls drain current Id

Last edited by adason; 5th June 2021 at 02:26 PM.
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Old 5th June 2021, 02:28 PM   #453
adason is offline adason  United States
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Originally Posted by OldDIY View Post
Change the polarity of the power supply and take VT1 type npn.
Filtering or stabilization can be introduced into the bias circuit (RC or RD).
Sell a germanium transistor for the price of a cow?
what is C4, 500pF cap for?

I will definitely add some caps on bias circuit, thanks
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Bias is voltage Vgs, and controls drain current Id

Last edited by adason; 5th June 2021 at 02:57 PM.
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Old 5th June 2021, 02:57 PM   #454
adason is offline adason  United States
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not bad so far...
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Old 5th June 2021, 03:12 PM   #455
jpatay is offline jpatay  Ukraine
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If you use a stabilized power supply, it will be very good. And select the germanium transistor with the highest gain.
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Old 5th June 2021, 06:33 PM   #456
adason is offline adason  United States
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done!
this is when cranked up at 20volts with LM317 regulator
distortion dropped to 0.076%, intermodulation at 0.101%
I will build another version, with bigger heatsinks
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Old 13th June 2021, 02:04 PM   #457
poynton is offline poynton  United Kingdom
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Hi All,

Did 2sb206 come in various packages eg TO3 or only the large size package?

I have seen these advertised on Fleabay

2SB206 Semiconductor - CASE: Standard MAKE: Generic | eBay

Very expensive and also the seller has sold me fakes before.

Andy
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Old 13th June 2021, 07:38 PM   #458
Soundhappy is offline Soundhappy  France
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@ Poynton
Look at this for all dimensions in mm and 44 gr weight of giant 2SB206 Germanium investigations
I am not aware about small version TO-3,
oh word "generic"....can be everything without datasheet..
Fig.26 or Fig.28 are the same dimensions of 2SB206
the others Fig. are tiny
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Old 21st June 2021, 12:40 PM   #459
poynton is offline poynton  United Kingdom
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I've just bought 4 2SB206 with heatsinks and fixing kits.

Maybe I'll build a class A stereo amplifier?
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Old 21st June 2021, 08:28 PM   #460
ElliotA is offline ElliotA  Europe
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Sounds like you're in the same boat as me, I'm going to put some in an Old Soul to start, that's my plan.
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