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In Reply to: RE: A Mercedes and a bus... posted by andy evans on March 10, 2015 at 06:54:15
Exactly ! If there was 10A passing through that choke I could understand the use of that wire . According to Jeff's mentor , Dr Halijak :
'A choke must have some internal resistance and its non-standard figure of merit is the ratio R over L. The best choke is the one with the smallest figure of merit and the best power supply has the least series resistance. It is not too difficult to obtain R over L = 10 but one can easily obtain R over L = 30 or more. The latter should be avoided but the ongoing shows that in a way it is unavoidable.'
Those chokes have a F.O.M of 7.8/0.32=24.75 which is on the borderline between low-fi and audio junk . A slight contradiction but according to Jeff and his rather small band of choke-choppers , it is a worthwhile mod...
Al
Follow Ups:
"Those chokes have a F.O.M of 7.8/0.32=24.75 which is on the borderline between low-fi and audio junk ."
But what happens when we look at the rest of what Dr. Halijak had to say?
" 15 ( choke ) + 70 ( rectifier ) + 70 ( power transformer resistances )
------------------------------------------------------------------- = 103
1.5 ( HY )
( the 70 ohm power transformer resistance is a guess )
If four 5U4GB are placed in parallel one has :
15 + (0.25 ) ( 70 ) + 70
___ = 68
1.5
Both figures of merit are way above the original 10 but your listening experiment told you that 68 was alright; this actual figure of merit is the best you can do because the largest power transformer was used and the smallest resistance available choke was used. You can see that stock power supplies are not anywhere near being the best cases *. Most tube and transistor electronic engineers are unconcious about power supplies, but good.
* Also the best cases need not have zero internal resistance - a utopian goal. One strives for minimal non-zero resistance !! "
To me that says that the resistance of all the chokes and the power transformer needs to be as low as possible.
What's wrong with that?
Well, Dr. Halijak doesn't get into what other problems arise when the DCR is low.
1. unless you have a critical inductance input choke the rectifier tube has a minimum series resistance per plate requirement that will not be meet.
2. Using chokes with really low DRC makes to harder to "tune" the supply so that it doesn't ring.
I would still like to have my question from years ago answered.
"What is the effective DCR of a power supply for the period of time, each cycle, while both diodes are simultaneously off (not conducting)?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Chokes also have to be " 20 Ohms or less " which was the VERY FIRST THING my audio mentor, Bob Fulton, told me in 1982 when I started with DHT amps.
Bet 99% are well over 20 Ohms. Thats simply mid-fi AL !!!
Under 20 Ohms is hi fi, under 10 Ohms is ultra hi fi. Very simple !!!
Combine Dr. Halijak and Bob Fulton, and you got a chance at a pretty good amp, but do not lose 3/4s of the luggage in the wiring.
Jeff Medwin
What I usually do is more or less go for a critical inductance input choke (sometimes slightly under the calculated numbers) and an additional (usually 2.5-5H) filtering choke for SE . I always place a small value cap after the rectifier . Neither of the chokes have anything like a 20 ohm DCR but have a much higher F.O.M of your Stancor chokes , no matter what you do to the leadouts :) In terms of relative DCR that F.O.M thing has a lot going for it . Have you just distorted the requirement for inductance that your first mentor used and just gone to low mass like your current mentor uses ? You know , the one with the cowboy hat , cowboy logic and the mudpumps...
On a side note I have a humungous new old stock 3H choke . 4 ohms DCR 1A rated . It weighs 15kgs .
Try fitting that on a chassis . Work out the F.O.M of it :)
Al
Dr. Halijak was brilliant, and I am GLAD you kept his contribution which I shared up here. Hey, someones paying attention. Dennis is alive, Messers . Fulton and Halijak are gone, and, I have the pleasure of Dennis' company for 30 years, and, heard his LOVELY amps at RMAFs, for maybe 8 years. What I hear of his impresses me Al.
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