The Singing Bush

Official Court Jester
Joined 2003
Paid Member
THF51S , Ser. 1X4343, 8R load

same conditions

further Ugs value , Ugs -4V01
 

Attachments

  • 1W 8R.png
    1W 8R.png
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  • THD vs. Freq 8R.png
    THD vs. Freq 8R.png
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  • FR 8R.png
    FR 8R.png
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  • 45W 8R 10%.png
    45W 8R 10%.png
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  • 40W 8R.png
    40W 8R.png
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  • 30W 8R.png
    30W 8R.png
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  • 20W 8R.png
    20W 8R.png
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  • 10W 8R.png
    10W 8R.png
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  • 5W 8R.png
    5W 8R.png
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Official Court Jester
Joined 2003
Paid Member
THF51S , Ser. 1X4343, 4R load

same conditions

again, further Ugs value , Ugs -4V01
 

Attachments

  • THD vs. Freq 4R.png
    THD vs. Freq 4R.png
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  • FR 4R.png
    FR 4R.png
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  • 25W 4R 10%.png
    25W 4R 10%.png
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  • 20W 4R.png
    20W 4R.png
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  • 10W 4R.png
    10W 4R.png
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  • 5W 4R.png
    5W 4R.png
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  • 1W 4R.png
    1W 4R.png
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Official Court Jester
Joined 2003
Paid Member
THF51S , Ser. 1X0117, 8R load

same conditions

furthest Ugs value , Ugs -4V41
 

Attachments

  • THD vs. Freq 8R.png
    THD vs. Freq 8R.png
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  • FR 8R.png
    FR 8R.png
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  • 40.5W 8R 10%.png
    40.5W 8R 10%.png
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  • 40W 8R.png
    40W 8R.png
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  • 30W 8R.png
    30W 8R.png
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  • 20W 8R.png
    20W 8R.png
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  • 10W 8R.png
    10W 8R.png
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  • 5W 8R.png
    5W 8R.png
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  • 1W 8R.png
    1W 8R.png
    39.1 KB · Views: 154
Official Court Jester
Joined 2003
Paid Member
THF51S , Ser. 1X0117, 4R load

same conditions

again , furthest Ugs value , Ugs -4V41
 

Attachments

  • THD vs. Freq 4R.png
    THD vs. Freq 4R.png
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  • FR 4R.png
    FR 4R.png
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  • 24W 4R 10%.png
    24W 4R 10%.png
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  • 20W 4R.png
    20W 4R.png
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  • 10W 4R.png
    10W 4R.png
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  • 5W 4R.png
    5W 4R.png
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  • 1W 4R.png
    1W 4R.png
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Official Court Jester
Joined 2003
Paid Member
2SK182ES, Ser. 1Y1362 , 8R load

Rail 65Vdc

Iq 2A3

output node 35Vdc

Mu resistor string 6 x 0R1

output taken 02R from top

this one , Ugs -2V02
 

Attachments

  • THD vs. Freq 8R.png
    THD vs. Freq 8R.png
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  • FR 8R.png
    FR 8R.png
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  • 49W 8R 10%.png
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  • 40W 8R.png
    40W 8R.png
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  • 30W 8R.png
    30W 8R.png
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  • 20W 8R.png
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  • 10W 8R.png
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  • 5W 8R.png
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  • 1W 8R.png
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Official Court Jester
Joined 2003
Paid Member
2SK182ES, Ser. 1Y1362 , 4R load

same conditions

again, this one , Ugs -2V02
 

Attachments

  • THD vs. Freq 4R.png
    THD vs. Freq 4R.png
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  • FR 4R.png
    FR 4R.png
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  • 44W 4R 10%.png
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  • 30W 4R.png
    30W 4R.png
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  • 20W 4R.png
    20W 4R.png
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  • 10W 4R.png
    10W 4R.png
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  • 5W 4R.png
    5W 4R.png
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  • 1W 4R.png
    1W 4R.png
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Official Court Jester
Joined 2003
Paid Member
2SK182ES, Ser. 1Y1363 , 8R load

same conditions

this one, all the way to other side , Ugs -4V97
 

Attachments

  • THD vs.Freq. 8R.png
    THD vs.Freq. 8R.png
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  • FR 8R.png
    FR 8R.png
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  • 65W 8R 10%.png
    65W 8R 10%.png
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  • 50W 8R.png
    50W 8R.png
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  • 40W 8R.png
    40W 8R.png
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  • 30W 8R.png
    30W 8R.png
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  • 20W 8R.png
    20W 8R.png
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  • 10W 8R.png
    10W 8R.png
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  • 5W 8R.png
    5W 8R.png
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  • 1W 8R.png
    1W 8R.png
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Official Court Jester
Joined 2003
Paid Member
2SK182ES, Ser. 1Y1363 , 4R load

same conditions

again,this one, all the way to other side , Ugs -4V97
 

Attachments

  • THD vs. Freq 4R.png
    THD vs. Freq 4R.png
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  • FR 4R.png
    FR 4R.png
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  • 54W 4R 10%.png
    54W 4R 10%.png
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  • 40W 4R.png
    40W 4R.png
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  • 30W 4R.png
    30W 4R.png
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  • 20W 4R.png
    20W 4R.png
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  • 10W 4R.png
    10W 4R.png
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  • 5W 4R.png
    5W 4R.png
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  • 1W 4R.png
    1W 4R.png
    36.8 KB · Views: 147
Official Court Jester
Joined 2003
Paid Member
Conclusions ........

I'm going to make a little pause here ... to let things settle in my head and to re-check graphs little more

in case that's easier for you to grasp things , find complete measurements in one rar file here : Dropbox - Singing Bush measurements.rar - Simplify your life

I know that I didn't took gain measurements in latest tests , was lazy , but that data is of secondary importance here

anyway , first and most important conclusion is - if you have any of those SITs , and you have way of measuring THD spectra ( if I can , everybody can) , The World is your Oyster - no reason that you can't build it and squeeze last ounce of performance , whatever value of Ugs your SITs have .....

even if it's preferable to have that pair close by Ugs
 
Member
Joined 2012
Paid Member
Thanks for all of the work, Zen Mod.

I have 62.5V available so I will increase my string from 4 x 0.1R to 5 x 0.1R and decrease Vds of the THF and give it a try with lower H2. I have quite high H2 right now. Who knows which operating point I will prefer.

I have already tried in in LTSpice and there was a substantial drop in H2.
 
Official Court Jester
Joined 2003
Paid Member
ook Spice , in this phase

you need to alter model to represent your exact SIT , as lhquam did show in his thread ...... and as you can see here , by measurements

luckily , due to Mu above , rail voltage is not so influential as SIT Uds voltage is ; so , vary Uds and Iq and Mu take-out point ..... good thing is - rail will go up , with decrease of Iq
 
Member
Joined 2012
Paid Member
I have modified my THF-51S right channel, which has the higher distortion. I added one 0R1 resistor in the string between the IXFN and THF and took the output at 0R2 above the THF ( total 5 x 0R1 ).

8R load at output

V+=63.2V (at 2W, did not check at other output levels), original was 62.5V

Iq=2.54A at 2W, dropping to 2.39A at 50W, original was 3.25A

THF Vds=35.5V, varying slightly at output levels, original was 29.0V

Measured distortion levels are similar to Zen Mod's measurements.

Below is measured distortion at 2W for original operating point, followed by revised operating point measurements at 2W, 5W, 10W, 20W, 30W, 40W, and 50W.

The original had 2.33% THD and the revised has 1.00% THD at 2W into 8R - quite a difference.

Now to revise the left channel and do some listening.

Edit: Typo in titles of measurements - should be Vds, not Vgs
 

Attachments

  • Right Iq 2,41 Vgs 5,9V 8R 40W.jpg
    Right Iq 2,41 Vgs 5,9V 8R 40W.jpg
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  • Right Iq 2,44 Vgs 36,2V 8R 30W.jpg
    Right Iq 2,44 Vgs 36,2V 8R 30W.jpg
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  • Right Iq 2,48 Vgs 36,1V 8R 20W.jpg
    Right Iq 2,48 Vgs 36,1V 8R 20W.jpg
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  • Right Iq 2,51A Vgs 35,8V 8R 10W.jpg
    Right Iq 2,51A Vgs 35,8V 8R 10W.jpg
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  • Right Iq 2,52A Vgs 35,6V 8R 5W.jpg
    Right Iq 2,52A Vgs 35,6V 8R 5W.jpg
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  • Right Iq 2,54A Vgs 35,5V 8R 2W.jpg
    Right Iq 2,54A Vgs 35,5V 8R 2W.jpg
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  • BAF2015 THF-51S Right Ch 62,5V 3,25A Vds=29,0V Sp out C 8R 2W.jpg
    BAF2015 THF-51S Right Ch 62,5V 3,25A Vds=29,0V Sp out C 8R 2W.jpg
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  • Right Iq 2,39 Vgs 35,1V 8R 50W.jpg
    Right Iq 2,39 Vgs 35,1V 8R 50W.jpg
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Last edited:
Member
Joined 2012
Paid Member
No verdict yet. I have only one channel revised. A SissySIT is providing power right now.

Because my amps were already finished, and built in a compact package, it took me quite a bit of time to take it apart, make the change, and put it back together, and also make sure that I didn't make any mistakes. Then the tests took a bit of time. I will make the change to the second channel tomorrow and then do some listening.

For preamp I have a Michael Rothacher designed Luminaria with 2SK82 and my speakers are Avantgarde Uno Series 2 (about 20 years old).