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Old 19th April 2005, 01:46 PM   #1
Mike L. is offline Mike L.  United States
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Default SE Output Primary Impedence

Hello all,

I have been re-reading an article in the April 2004 issue of Audio Express titles "Easy-to-Build, Low-Cost SE Amp". The subject of the article uses 12L6 output tubes to yield about 3.5 watts.

In researching these tubes, the output power is stated for a 4000 ohm load. I assume that the 4000 ohm load would be the impedance of the output transformer primary.

If I was to parallel a second output tube in order to obtain more power, would I need to halve the transformer primary impedance?

Thank you.
Mike L.
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Old 19th April 2005, 03:02 PM   #2
dhaen is offline dhaen  Europe
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Default You are right if...

If the 4000 ohms is between 1/3 and 1/2 of the tubes Rp then that's what you want.
Parallelled tubes ideally need to see 1/n of single tube impedance. Eg 1/2 for 2 tubes.

John
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Old 20th April 2005, 11:16 AM   #3
kmtang is offline kmtang  Canada
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According to RCA's data sheet, the 6L6 could use 4.5K as the plate load for SE class A operation.


JOHnny
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Old 20th April 2005, 11:21 AM   #4
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Default getting rid of DC

hello,

I've been to an audio-show and it gave me some stuff to think about.

There was an philosophy about getting rid of the d.c. in SE output transformers.....
This is done by putting a coil in the anode line....At the output of the tube you place a capacitor that goes to the output-transformer....
Now you don't have the dc in the outputtransformer...

(in depth info will be available on www.mennovanderveen.nl)

Will this sound nice??? i think so, what are your ideas about this????
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Old 20th April 2005, 11:35 AM   #5
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Quote:
Originally posted by kmtang
According to RCA's data sheet, the 6L6 could use 4.5K as the plate load for SE class A operation.


JOHnny

Be aware that the 12L6 is not the same tube as the 6L6.
It's a 50L6 with a 12 volt filament.
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Old 20th April 2005, 11:38 AM   #6
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Default Re: getting rid of DC

Quote:
Originally posted by kathodyne
This is done by putting a coil in the anode line....At the output of the tube you place a capacitor that goes to the output-transformer....
Now you don't have the dc in the outputtransformer...
This is known as choke-loaded shunt feed, or more commonly known nowadays, as parafeed. You might be able to dig up a few more references and opinion about the "sound" of this type of circuit by searching for "parafeed"
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Old 20th April 2005, 11:54 AM   #7
Yvesm is offline Yvesm  France
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Quote:
Now you don't have the dc in the outputtransformer...
... wich has both advantages and disadvantages !

Yves
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