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Old 14th January 2003, 02:08 PM   #11
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Basically you have a psu that would be similar to what would drive a 300b imho..you might want a little more juice.. looking at quite a few 300b or el34 designs leads you to a transformer of around 400v! Don't forget your output transformers drops 30-40v of the b+ as well before you get the plate voltage.

The tranformer being from sowter you can specify several taps! Is that not a grand idea ;-).. Get taps at 300, 350, 400, 450 won't be that much more work for the tranniebuilders...they just have to pause add a tap and continue winding...(450 might actually be to much)

If you are going to use one transformer which would be the best value for money seeing that money is tight and you might want chokes..get one nice fat tranny for both channels that can supply say 400/500mA. Use one big choke and so you have clc for both channels then split into rc for each channel.
Hope this helps..
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Old 14th January 2003, 02:53 PM   #12
dhaen is offline dhaen  Europe
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Space is at a premium?

Mount the choke underneath the chassis directly under the power transformer. Make sure you get one with "Frame" construction, then you can mount it with it's field at 90 degrees with respect to the mains transformer AND to the output transformer(s).

Cost:

You've already explained why you want to use Sowter for your mains and output transformers. But the choke could be obtained cheaper locally. When mounted underneath, appearance is less important.

Cheers,
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Old 14th January 2003, 02:56 PM   #13
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Agree with John, you could get Lundahl chokes...but they don't have any 500mA chokes..however you could parallel two 250mA chokes..
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Old 14th January 2003, 03:02 PM   #14
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Mikael,

Two minor points...the plate resistors for the 6n1p needs to be only 1 watt..

And the cathode bypass cap for the 6n1p should be a rated closer to 25 volts to be safe..
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Old 14th January 2003, 03:30 PM   #15
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Also consider the Lundahl chokes. They're very compact and as tough as nails. Should be cheap too as they're in Sweden.

Chokes are good. They're your friends. Think of them as your little helpers in the power supply
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Old 14th January 2003, 03:44 PM   #16
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Default sorry

Choke and inductor are just different terminology for the same thing then, when refer to it in a speaker crossover it is called coil, when refer to it in a Pi filter it is called inductor, when it is on its own it is called choke, when it is connect to the mains it is call transformer, when connects to a speaker it is call output choke?
Am I correct with these assumptions?
Thanks
Chris
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Old 14th January 2003, 03:54 PM   #17
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Default Choke

I think the term choke is specifically used to indicate the use of a coil or inductor, like to "choke" the ripple on a supply line. I haven't seen it used for filters or output inductors.

Jan Didden
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Old 14th January 2003, 05:46 PM   #18
dhaen is offline dhaen  Europe
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Default Choke

You can also have RF chokes. They're just inductors too.

I think "choke" is a rather old fashioned term i.e.

choke = inductor
condenser = capacitor
resistance = resistor

cheers,
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Old 14th January 2003, 06:11 PM   #19
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Default CHOKING

Hi,

Well I think the name "choke" referes to the function (service) it was used for namely, as Jan stated to choke/strangle ripple from the PSU.

Although it has nice side effects such as isolating the PSU from its' circuit as well providing an almost infinite impedance.

It also tends to regulate the PSU.

When I hear" inductor" I automatically think about x-over designs for LS use (air-core inductors).

Terminology can be confusing,
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Frank
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Old 14th January 2003, 08:26 PM   #20
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I would like to thank everyone that answered to my question! You guys are great.

Right now I'm checking my finances to see if there is room for a choked PSU, and I must say... It looks promising. I think i will go for a mains transformer with two sec. for B+ (one winding for each channel). So I will probably get two 20H 150mA chokes from sowter. I think the amp will draw 110-120mA per channel so 150mA should be enough.

Ohh... btw... Does anyone have any bias-suggestions for the KT88? When I studied the spec-sheets from svetlana they seem to recommend 105mA, thats why i thought 120mA would be enough for the whole circuit.

Bas... the reason I placed a 10W plate-resistor on the 6n1p is simple. The place I order all my components from (Elfa) only had 47k at 10W. Is it bad to have 10W instead of 1W?
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