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Old 1st August 2012, 02:34 PM   #491
Zen Mod is offline Zen Mod  Serbia
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Originally Posted by flg View Post
......
But, it's good to be driving primary's R with 1/10th source impeadance.......


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just tested ( to refresh my weak memory) those repeater coils (pictured in one of my previous post)

exacttype is Iskra TL-1M , so called 600:600 , in fact 4 x 150R

two primaries connected in parallel , fed with siggene , 50 ohms tap

CRO across one secondary , loaded with 6K8 (estimated range of load in F6 )

it's 'ookin' linear 15Hz-58Khz , and up to 280Khz ;

there is some rise in few freqs between 58KHz and 180KHz , but nothing what appropriate RC loading can't handle

and they're primary made for telephone range

but do not forget some other wakoo implementations of telephone transmission lines - teleprinters and other crazy military purposes
considering that I'm expecting that loading impedance of each (of two ) output's gate circuits is in range of 5-10K , we can freely say that load reflected to buffer is (5-10K)//(5-10K) = 2K5-5K ; that's good enough , at least in my neck of wood

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Last edited by Zen Mod; 1st August 2012 at 02:39 PM.
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Old 1st August 2012, 03:29 PM   #492
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yes , of course ; two identical 600:600 xformers , both primaries in parallel (in phase ) , then secondaries as drawn

in that case - it will buffer going to be happier than driving two (Jensen's) 150R primaries in parallel ?

that's strictly matter of blending with primary inductance , not matter of impedance ; xformers are - so called - 600:600 or whatever - those numbers are information of intended purpose ( each one dictating inductance and Rdc of windings ) but , generally speaking , one can find xformer specimens with similar inductance , one called 150 Ohms , other one called 600 Ohms , third one called 1K Ohms .

in this ( and many other cases ) reflected impedance to source , in this case load which buffer is seeing , is matter of input impedance of each output gate mechanismus , then these two in parallel ...... then that transferred 1:1 through winding ratio back to buffer

conclusion - ratio is what's counts most , combined with load ; only knowing (or anticipating these during construction ) we can say how's source-xformer-load combo called , in regard to how-many-Ohms

then - depending how much inductance is (so called 150, or so called 600, or so called 1K , whatever) in primary - that will reflect in left F3 , phase behavior etc.

higher range (impedance ) xformer will be safer regarding left F3 and phase behavior , but it will present more troubles in right F3 (capacitance between windings ! ) and slightly worse generator for gates (of output Jfets)

whoa ! I'm sorta spinnin' in circles now ......

Do we have any confirmation from Papa that 2 x 2-winding transformers with have the same behaviour as 1 x 4 winding transformer? In an earlier post F6 Amplifier he refers to the "quadfilar windings have symmetric capacitance, so all windings exhibit the same conditions with respect to that" . It seems to me that with one transformer there would be more capacitive coupling between the transformer secondaries than with 2 transformers.
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Old 1st August 2012, 03:51 PM   #493
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capacitance issue - nothing to write home about

xformer is either good for purpose , or is bad for purpose , nested in entire shebang

have some faith in Pa (and his choices) , or go build Halcro
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Old 1st August 2012, 04:34 PM   #494
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One aspect about the transformer as used in Nelson's F6 schematic has me wondering. That is the DC (front end bias current) across the primary. That could easily saturate the core of a simple off the shelf part. Am I missing something?

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Old 1st August 2012, 04:49 PM   #495
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DC? Bias flows from + to - supply. Only a small offset current "may" flow thru the primary...
ZM, oh mighty one
According to Bill Whitlock, I'm sure you recognise the name, sited in a post many posts ago, and likely the engineer involved in the F6 Xfrmr, says; "the distortion performance of ANY transformer is significantly improved when the driving source impedance is less than the dc resistance of the primary. However, little is gained below about 10% of the winding dc resistance."
So, my "150" ohm primaries are about 28 ohms DC. Ohms not turns, not L, not Z, and if those Jensens are the same, and they seem to be, we have not satisfied a design requirement Bill thought important??? do you have any comment on that idea. I know I stated that already but you responded to freq resp issues instead
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Old 1st August 2012, 05:48 PM   #496
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Yup. I missed something. Thanks.
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Old 1st August 2012, 06:10 PM   #497
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Quote:
Originally Posted by steve jones View Post
One aspect about the transformer as used in Nelson's F6 schematic has me wondering. That is the DC (front end bias current) across the primary. That could easily saturate the core of a simple off the shelf part. Am I missing something?
that's simplified sch ; I'll not disclose too much if I say that Pa certainly isn't allowing DC through windings ;

patience please

Quote:
Originally Posted by flg View Post
DC? Bias flows from + to - supply. Only a small offset current "may" flow thru the primary...
ZM, oh mighty one
According to Bill Whitlock, I'm sure you recognise the name, sited in a post many posts ago, and likely the engineer involved in the F6 Xfrmr, says; "the distortion performance of ANY transformer is significantly improved when the driving source impedance is less than the dc resistance of the primary. However, little is gained below about 10% of the winding dc resistance."
So, my "150" ohm primaries are about 28 ohms DC. Ohms not turns, not L, not Z, and if those Jensens are the same, and they seem to be, we have not satisfied a design requirement Bill thought important??? do you have any comment on that idea. I know I stated that already but you responded to freq resp issues instead
moi already stated what's carved in stone in post regarding crude test of Iskra repeaters ; their Rdc is 18 Ohms per winding (so around 9 ohms when primaries are paralleled )

what can I say - some rules o' thumb are more critical than other ones

we always must look at broader picture - what's reflected impedance , is there DC across primary ...
I'm far of being xformer xpert , just trying to get why they're working so well - either driven with proper buffer or even ditto from DAC chip output
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Last edited by Zen Mod; 1st August 2012 at 06:14 PM.
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Old 1st August 2012, 07:20 PM   #498
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ZM, O.K. I understand
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Old 1st August 2012, 08:27 PM   #499
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On the subject of the transformer's load on the input buffer, the feedback raises the apparent impedance of the tranformer primary because the feedback end of the primary moves in phase with the end driven by the buffer.
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Old 1st August 2012, 09:47 PM   #500
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certainly ;

by which amount ,we'll see when Pa reveal final schm , when we can see what's amount of feedback

edit:

whoopsie!

post #500

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