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JandG 13th September 2008 02:54 AM

2 stage SE IT coupled amps..
I am wondering who all use a simple 2 stage SE IT coupled amp as thier choice of music pleasure. I am using a 6sn7/6v6 SE in UL & IT coupled. IT are O'Netics level II & OT Hashimoto H-20-7U. Fixed bias on 6v6 using batteries & cathode battery bias on 6sn7. I find when fixed bias on output in combination with good IT's & OT that the music gets seriouse. Even a ratshack pot in these simple IT coupled circuiuts produce some of the best sonics I have ever heard. I perposely tried differnat pots to see if it was extreme importance in these circuits. I have decided it is not. After 3 months of bias experiments with 26/27/or 6sn7 as drivers for SE 6v6 in UL & IT coupled, that fixed bias & especially with batteries is a very large step forward. This combo with any decent speaker is extremelly holographic. Bud P might just build some of the best IT's in the world. This will play out in time. It is of intrest to me in hearing from members that actually listen to 2 stage IT coupled amps for certain music or all of it. & a great big smile for battery fixed bias in this house. I do not yet have schematic drawn up for this amp but will soon. circuit & op-points are finalized .

jrdmedford 14th September 2008 01:35 AM

The nice thing about IT's is you get the advantages of an plate
choke on the driver, and a grid choke on the output tube all in the
same package! :)

Many are doing 2-stage IT coupling. My experience is with Lundahl (1660/SE, 1660/PP), Electra-Print (SE). These products
are quite different: Lundahl's use sectioned and layered
primary and secondary windings. The EP's are bifilar wound.
Both strategies attempt to deal with the same interwinding
capacitance problem in different ways. The bifilar winding has
the least stray C - which is why they they have exceptionally
good HF performance... The interleaved technique is technically a more electrically reliable part - because the teflon film that separates each primary/secondary winding is more mechanically reliable than the insulation polymer that separate bifilar windings (which lay side-by-side). In most extreme situations, one MIGHT
have 600V potential difference between primary and secondary
windings (Consider a 300B driver at 400V on the primary, and
an 845 grid at -130V on the secondary) ; in such cases - the
breakdown of insulation between primary/secondary can be catastrophic to the output stage.

-- Jim

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