SE Output Primary Impedence

[Mike L.]

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]

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]

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


JOHnny

 

[kathodyne]

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]

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]

Re: getting rid of DC

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]

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

... wich has both advantages and disadvantages !

Yves