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??? Output Transformer - Silicon Steel or Amorphous
??? Output Transformer - Silicon Steel or Amorphous
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Old 7th December 2017, 04:23 PM   #91
andyjevans is offline andyjevans  United Kingdom
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Quote:
Originally Posted by euro21 View Post
Why?
10/801 working with 7-10k OPT.
10k at 20Hz is only 80H.
You made a good point, so I tested it out. 10Y with a single 126C at 100H against 2 in series at 200H, used just as plate chokes.

Conclusion is that the 200H of two in series is clearly better sounding - more detail and clarity, better timbre, more treble definition and air. Better all round in fact. The single 126C clearly works, but it's rather flat and dead sounding in comparison, and with an audible loss of clarity. These are cheap units and anyone thinking of using them with higher Ra tubes like 26 and 10Y should, in my opinion, go for two in series. If I order a different plate choke for the 10Y I'd be wanting 200H on the basis of this test, but with a different make who knows - results might not be the same?
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Old 7th December 2017, 04:28 PM   #92
Blitz is offline Blitz
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Andy, that's a great finding...I would never thought about this like this...I would have expected the opposite: Better bass response with more inductance, but a less engaging sound as the dc-resistance goes up like a cheap choke vs. an expensive one...

So, great finding, will try this
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Old 7th December 2017, 06:07 PM   #93
john_tracy is offline john_tracy  United States
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Quote:
more detail and clarity, better timbre, more treble definition and air
If one thinks about a plate choke as a current source load, these are exactly the results that I have experienced with active CCS loads when replacing an inferior current source with one that is superior. For example, a cascode DN2540/DN2540 vs. a single 10M40 or an IXYS 8N50D2/1N100D vs. a DN2540/DN2540.
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Old 7th December 2017, 07:06 PM   #94
Blitz is offline Blitz
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So, do I understand you right that Ixys 8N50D2/1N100D is the best CCS ? A bit off topic, sorry, ut that is very interesting...as I wanted to test anode chokes vs. ccs...
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Old 7th December 2017, 07:28 PM   #95
john_tracy is offline john_tracy  United States
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I'm not saying it's the best. It is better than the DN2540 cascode. There are caveats: if the current is less than 10mA you might want to look elsewhere Although I am currently using it as a plate load for a 6SN7 @8mA and it sounds very good), also the IXYS cascode really needs ~30V across it to perform well (also allow for the anticipated signal swing). If you want to experiment, Kevin Carter @K&K Audio sells CCS kits that are very handy and real cheap and they are supplied with IXYS MOSFETs.
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Old 7th December 2017, 07:49 PM   #96
euro21 is offline euro21  Hungary
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??? Output Transformer - Silicon Steel or Amorphous
Quote:
Originally Posted by andyjevans View Post
You made a good point, so I tested it out.
Are you measured interwinding capacitance?
126C is 4W 10k:10k bifilar output transformer, so it's not a real plate choke design (not optimised to low capacitance -not segmented- and don't know how many layer inside).

Last edited by euro21; 7th December 2017 at 07:52 PM.
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Old 7th December 2017, 07:53 PM   #97
sser2 is offline sser2  United States
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Two audio chokes in series halves the winding capacitance, extending high frequency response of the combo.

Even better idea is two dissimilar chokes in series, a cheap LF choke with high inductance and high winding capacitance, and good quality HF choke with low inductance and low winding capacitance. The HF choke is something like 1-2 H with a highly sectioned winding and gapped ferrite core.

LF choke provides for low bass extension by virtue of its high inductance. HF choke determines treble extension by virtue of its high self-resonance frequency.
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Old 7th December 2017, 08:25 PM   #98
pieter t is offline pieter t  Netherlands
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Originally Posted by sser2 View Post
One lot of Midcom 671-8422 transformers had unbelievable 480 H inductance per side. This is in a transformer 3/4 by 3/4 inch and winding DCR of 120 Ohms! I thought there was something wrong with measurement, but in the same test larger Midcom transformers (671-8000) were 11 H per side, as of specs.
That is nothing special by todays modern material standards.
I measured a just finished autoformer volume control, wound on a nanocrystalline toroidal core with Afe of 0,86 cm² (some 0,13 inch²).
DCR 31 ohm; inductance 160 H.
Enough winding space on that toroid for about 4 times the turns to get near 120 ohms DCR; that would give an inductance of some 2400 H
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Old 7th December 2017, 09:25 PM   #99
sser2 is offline sser2  United States
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Originally Posted by pieter t View Post
autoformer volume control, wound on a nanocrystalline toroidal core
Yes, these nanocrystalline cores are amazing! I am making a similar TVC with a toroid Vitroperm core from Vacuumschmelze (sold by Mouser). Low number of turns for high inductance, so an easy DIY project.

However, how stable these amorphous/nanocrystalline materials are remains an open question. High magnetic properties depend on crystal structure, and all materials re-crystallize slowly even at room temperature. I noticed that there are two types of Vitroperm cores, one encased in rigid plastic sheath, and the other (cheaper one) coated with epoxy. Although core material is the same, the encased core has 3 times the guaranteed permeability of the epoxy-coated core. This means one thing: permeability is extremely sensitive to any kind of mechanical strain, exactly like in 80% Ni cores.
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Old 7th December 2017, 09:53 PM   #100
pieter t is offline pieter t  Netherlands
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These are exactly the cores I am using (Vakuumschmelze Vitroperm), the encased in rigid plastic enclosure types.
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