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Old 7th November 2013, 03:01 AM   #11
The Dastardly Dad of Three
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Might wanna watch the VDS rating of the sit. Iirc it's 240v and I *think* it's a good idea to account for the doubled voltage swing across the inductor.
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Old 7th November 2013, 08:46 AM   #12
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Originally Posted by Junm View Post
Nice Hybrid... is the Impedance ratio of your OPT is it 53//8r ,and how many watts you squeeze from it?

Did you try using SE OPT only without the parafeed with higher A+(150v or higher) and lower idle current?
I didnt measure it. This needs to be done yet. I assume 10-11W.
I didnt use air gapped OPT. Maybe someone could make it,
but I guess it would be very expensive.
Higer A+ is possible, but you need to watch the power dissipation not more
then 50W for the 2SK82.
Also the input capacitance would be nice to know for this operaion point.
I can only assume that its lower then in high current low voltage operation.
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Old 7th November 2013, 10:55 AM   #13
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Originally Posted by Junm View Post
Nice Hybrid... is the Impedance ratio of your OPT is it 53//8r ,and how many watts you squeeze from it?

Did you try using SE OPT only without the parafeed with higher A+(150v or higher) and lower idle current?
The impedance ratio of UTC LS-33 is 50R to 7.5R.
Very practical this matching transformer. I can connect speakers and headphones from 1,2-500R impedance.
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Old 8th November 2013, 03:20 AM   #14
Junm is offline Junm  Philippines
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Thanks..i will try to do it whenever i have done my current projects but in my case a 2sk60 in parallel will be used...
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Old 9th November 2013, 10:49 AM   #15
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Originally Posted by Junm View Post
Thanks..i will try to do it whenever i have done my current projects but in my case a 2sk60 in parallel will be used...
Ok. Let me know the results...)
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Old 5th December 2013, 07:14 PM   #16
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After a good month of listening to the latest revison as pictured in the schematic I finally tried something really different. I loaded the driver tube whit Garry Pimms CCS and used the MU out to the 2SK82. At first I expected a more SS sound but I must say after few days of listening I can say that this is the best amplifier I ever heard. It must be the right combination of harmonics I guess.) The output impedance of the driver stage is way lower whit the MU out and the SIT likes that! I also changed the drivers PSU a little bit. Now I use 20H choke whit 150DCR and the anode voltage is little higher around 178V and 35mA...
I even could lower the input impedance of the SIT to 10K.
I am really surprised whit this CCS.
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Old 11th December 2013, 07:36 PM   #17
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The other day I posted into wrong thread...
But here I am...
I am keeping posting for me as a diary...
I must say I made big improvement.
First of all I lowered the driver stage output impedance whit
CCS Mu follower output. Then I changed the cathode resistor and cap whit a
white diode (its a package in SMD whit two dioded in parallel). Forward voltage is
2.9V, so perfect. I get 180V at plate and 36mA current.
I also tried whit fixed bias on SIT but didnt work good. Its tooo much current drift couse of the unregulated supply...So maybe I will bypass the elnas whit 70-100uF Mkp or similar to get to cover the main frequencies down to aprox. 150hz...Will seee.
But this amp really sounds absolutly beautiful. There is some sort of sinergy grown between the SIT and the driver stage. It sound big and delicate but in no way harsh or SS like. This is a good candiate for a life time low power simple amp....
Now I will listen and will see how I can move on.......
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Old 11th December 2013, 09:11 PM   #18
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Hi DIYspaceW
That is interesting play with Your Sit parafeed wish You to find it
a absolute sweet spot.Thanks for sharing impressions about sound.
Great diy congratulation
Best regards
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Old 11th December 2013, 09:51 PM   #19
scholl is offline scholl  United States
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Hello,

Can we get more details on the choke? Inductance, core size, DCR etc.

I know of only one other successful true transformer loaded transistor amp and all my attempts failed. Seems the internal resistance is too low and the transistor shunts the transistor.

Thanks,

Scott
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Old 12th December 2013, 06:49 PM   #20
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Originally Posted by scholl View Post
Hello,

Can we get more details on the choke? Inductance, core size, DCR etc.

I know of only one other successful true transformer loaded transistor amp and all my attempts failed. Seems the internal resistance is too low and the transistor shunts the transistor.

Thanks,

Scott
Interesting never thougt of something like that....

The plate reactor has core size of 8,1cm * 10,2 cm * 6,9 cm. Its quite big and havy...Its from M6 grain oritented steel I think.
The inductance at 1A is 1H and whit lower currents more...DCR is aprox. 6-7 ohms...

It works well.....But if we talk about perfect world, I am a realist and can tell you there isnt a perfect or ideal world out there, so I am not looking for it...) This amp makes fun and joy...It just pictures the frequencies the way I like it. Thats all!
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