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Old 28th January 2003, 11:56 PM   #11
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Default Toroids


Toroids will work but the end result will very much depend on the quality of the core. So the final sound especially the highs is very much of a touch and go thing.
If you actually have the winding details(no of turns, layers etc), I know a guy in KL with Z11 grade core which will be adequate for OPTs and the price is very reasonable.
If you want to be sure, try Martin Electronics in Bencoolen Square in S'pore. He sells Lundahls at a price of about USD75 each.


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Old 1st February 2003, 01:53 PM   #12
316a is offline 316a  England
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Default toroids

nothing wrong with using toroids . Points to remember are to keep the DC well away from them and avoid saturation . I don't know about pre-amp usage but I've been using them as power amp outputs for the last year . Primary inductance is usually high but finding large enough sizes with the correct turns ratio can be tricky , this means that for power stages you need to drive with Low Ra valves . The main problem is the core size , when pushed hard the bass can fall apart but I doubt this should be a problem with pre-amp usage . Try them , they should work well for pre-amps . Best application to date for me is parallel feed , push pull is another possibility but you'll need to take into account balancing the output stage , keeping the HT low . Remember these things weren't designed to swing 400v p-p across them at 20Hz .

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Old 1st February 2003, 09:00 PM   #13
tiroth is offline tiroth  United States
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As promised:

1.6VA as line input
Primary inductance: 4.5H
Primary interwinding capacitance: 200pF

with 13k secondary load
-0.5dB at 20Hz
-0.3dB at 20kHz

The bad news is that distortion is on the order of 0.6% at 20Hz, -0.05% at 250Hz, 0.001% at 500Hz, and unmeasurable at higher frequencies. This would be excellant as line input for a tweeter amp, but the primary inductance just doesn't appear to be high enough for the low frequencies.

35VA as OPT
Primary inductance: 146H
Primary leakage inductance: 10.5mH
Primary interwinding capacitance: 1.4nF

Not bad!
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Old 1st February 2003, 09:11 PM   #14
316a is offline 316a  England
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Default line doughnuts

with my very basic primary inductance testing I usually get 100H for a 50VA 230V:6-0,6-0 unit at 50Hz . This is more or less the largest size with the highest turns ratio . Sizes above that such as 230:9-0,9-0 etc require the output valves to be 6C41/6C33 type things . I am also tempted to unwind the secondary windings and use as a push pull anode choke . Anyone ever thought of doing this ?

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Old 1st February 2003, 09:52 PM   #15
dhaen is offline dhaen  Europe
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How about using a CCS on one side, and then you can use the other side SE.
Nice for a driver anode choke?
You could even put a teeny amount of current feedback to the cathode from the 6v winding.

This is of course "pub talk"...

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Old 2nd February 2003, 04:36 AM   #16
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Default thanks guys

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