SE Output Primary Impedence

Mike L. · 19th April 2005, 01:46 PM

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, 03:02 PM

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, 11:16 AM

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, 11:21 AM

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, 11:35 AM

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, 11:38 AM

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, 11:54 AM

Quote:

Now you don't have the dc in the outputtransformer...

... wich has both advantages and disadvantages !

Yves

19th April 2005, 01:46 PM	#1
Mike L. diyAudio Member Join Date: Oct 2003 Location: Upstate New York	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.

19th April 2005, 03:02 PM	#2
dhaen diyAudio Moderator Emeritus Join Date: Jun 2002 Location: U.K.	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

20th April 2005, 11:21 AM	#4
kathodyne diyAudio Member Join Date: Feb 2005 Location: leeuwarden, netherlands	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???? __________________ emission over emittor

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20th April 2005, 11:16 AM	#3
kmtang diyAudio Member Join Date: Nov 2004 Location: Vancouver	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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