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-   -   SE Output Primary Impedence (http://www.diyaudio.com/forums/tubes-valves/55707-se-output-primary-impedence.html)

Mike L. 19th April 2005 02:46 PM

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.

dhaen 19th April 2005 04:02 PM

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

kmtang 20th April 2005 12:16 PM

According to RCA's data sheet, the 6L6 could use 4.5K as the plate load for SE class A operation.


JOHnny

kathodyne 20th April 2005 12:21 PM

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????

Frank Berry 20th April 2005 12:35 PM

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.

audiousername 20th April 2005 12:38 PM

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"

Yvesm 20th April 2005 12:54 PM

Quote:

Now you don't have the dc in the outputtransformer...
... wich has both advantages and disadvantages !

Yves


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