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What To Do With Those 2SJ28's
What To Do With Those 2SJ28's
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Old 18th June 2017, 06:50 PM   #221
Nelson Pass is offline Nelson Pass  United States
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What To Do With Those 2SJ28's
They are all fine. Being SITs, you can easily adjust the 2nd harmonic
amplitude and phase on all of them to get much the same effects.

One thing you might want to try is bridging two of these, one with the 2SJ
and the other with the 2SK.
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Old 18th June 2017, 08:22 PM   #222
BeardyWan is offline BeardyWan
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For lower distortion? I'm surprised you don't get better cancellation with two of the same sex.

I did try bridging two same sex on LtSpice, and it suggests that the THD is better, but I am doing something silly: I mirrored the circuit leaving two independent CCS's to enable independent adjustment of the idle current. But of course the circuit clips at the same point as with a single device. I assume whats happening is that as the current goes back and forth through the load, the maximum current limit is hit on `one side' and then the other and is limited by the CCS in either case. So it doesn't help dissipation or max power. I either need to get smarter or failing that I'm trying a circlotron

Last edited by BeardyWan; 18th June 2017 at 08:35 PM.
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Old 18th June 2017, 08:30 PM   #223
plasnu is offline plasnu  United States
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Quote:
Originally Posted by Nelson Pass View Post
One thing you might want to try is bridging two of these, one with the 2SJ
and the other with the 2SK.
I'm interested in the outcome.
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Old 19th June 2017, 06:27 PM   #224
Nelson Pass is offline Nelson Pass  United States
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What To Do With Those 2SJ28's
Quote:
Originally Posted by BeardyWan View Post
For lower distortion?
No, rather for the entertainment of having a 2nd harmonic character.
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Old 23rd June 2017, 11:37 PM   #225
BeardyWan is offline BeardyWan
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Default Vfet circlotron?

I keep looking at the attached and I am hoping (expecting) for someone to educate me on the inevitable flaws in this cunning plan... apart from 600W of heating and (with luck), some good vibrations.

The Aleph CCS addition does make the CCS device `see' both sides of the amp, and to this end perhaps I could put the sensing resistor in the drain path of the gain device and shield it from the contribution of the other side with the cap in schematic (I tried this and couldn't seem to make it work). It would allow independence and better matching perhaps

Does cancellation via complementary pair or `balanced single ended' or circlotron pairing start to kill the `character' of a SIT and if so should we focus on a single device single ended toy?

As an aside how much influence does the choice of the device for the CCS make on the sound of the output? It seems a bit extravagant to run two 2sk180s in a single ended stage (one as the gain device and the other as the CCS). On the other hand, I'd guess as soon as you start using the mu or Aleph CCS then the 'CCS device' starts to play an increasing role

BeardyWan
Attached Files
File Type: asc 2sk180 Circlotron CD wiht aleph ccs.asc (6.3 KB, 56 views)

Last edited by BeardyWan; 23rd June 2017 at 11:42 PM.
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Old 24th June 2017, 09:12 PM   #226
ci11 is offline ci11  United States
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Quote:
Originally Posted by BeardyWan View Post
As an aside how much influence does the choice of the device for the CCS make on the sound of the output? It seems a bit extravagant to run two 2sk180s in a single ended stage (one as the gain device and the other as the CCS). On the other hand, I'd guess as soon as you start using the mu or Aleph CCS then the 'CCS device' starts to play an increasing role

BeardyWan
JAMA on this forum has already built the amp you are asking about: using the IXTN46N50L (a linear part, not a switch) as the CCS and driving 2x K180Ds. He even measured its H2/H3 performance and it's a deadringer for a 45 triode amp he built earlier. In other words, he has built a parallel 2SK180 SE amp that delivers 50W Class A into 4 Ohm!

Attached please find the approximate schematic and his own descriptions are here: BAF 2015 CoverageGreat work as usual, JAMA!
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File Type: jpg JAMA.jpg (112.9 KB, 460 views)
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Old 25th June 2017, 01:24 AM   #227
BeardyWan is offline BeardyWan
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Hi Ci11,

I was aware of JAMA success with this circuit, but I wasn't aware that he had tried multiple different CCS devices and found it made no difference to the sound.
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Old 25th June 2017, 01:37 AM   #228
ci11 is offline ci11  United States
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Quote:
Originally Posted by BeardyWan View Post
Hi Ci11,

I was aware of JAMA success with this circuit, but I wasn't aware that he had tried multiple different CCS devices and found it made no difference to the sound.
I do not know JAMA had tried diffeent devices for CCS including the K180, but he did deviate from the original BAF2015 circuit which uses the IXFN140N20P in both CCS and output. The linearity of the IXTN46N50L made it far easier to achieve a stable bias.

As to the sound, his schedule for the second channel build is later this year so he probably has not heard it on speakers yet - but his FFTs showing the amp's harmonic balance and that very lovely 10kHz square wave response are very interesting: what I glean from those measurements is a quiet, powerful SS amp with lightning fast reflexes and the harmonic character of a tube amp.

If he has time, I am sure he will weigh in and provide a lot more insight...he's a really great guy and a fearless builder.
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Old 30th June 2017, 01:55 AM   #229
davidinnewzealand is offline davidinnewzealand  New Zealand
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in Nelsons SIT-3 simple scheme, post #96 my question is:
What does the Transformer do? It has the prim/sec connected and one end to ground through a cap with the other end to the SIT gate?
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Old 30th June 2017, 05:44 AM   #230
BeardyWan is offline BeardyWan
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a `passive' voltage gain stage
but also isolates the dc bias voltage
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