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In Reply to: RE: Lundahl LL1620cfb posted by Stuben on December 17, 2014 at 10:11:22
That article is a SET amp
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The article is not for an SET. It for a single ended Pentode design.
Not sure what your'e reading...have another look.
Stuben
Here's an example...
I should have posted LL 1620cfb as used in a PP amplifier. The cfb winding is only 1/2 an ohm per your posted schematic?
Yep the secondary of the LL1682 is 1/2 ohm...
In light that you're not relying on the winding as a bias load, not an issue.
Just local output feedback...IT coupled amps are really not suitable for global feedback...With that said, I have only read that that this is the case...I haven't tried it yet..
The SE design on the K&K site employs, CF, Global and UL feedback for the SE EL34 RC coupled amp...neat article. 8 watts of power with no bleeding ears..according to the author.
Stuben
You will need to bias your output normally a then place the feedback windings between your bias resisters and ground. The old classic Quad monos used a CF winding in the primaries..seems like Mac also did something similar.
I like the sound of pentodes when done well. Many on the forum would question why not just go with triodes...I have built both and I alternate depending on the music and mood...same for SE and PP. Both have qualities that are different..lots of fun...
Stuben
I dont understand. Isnt that schematic just showing ac feedback using the speaker winding?
What I wondered recently that even stock 1620 trans has 8 seperate output windings. Why cant you just hack one of those for a proper feedback winding or 2 even.
I have a pair of softones I bought for thier feedback windings.
I didn't answer you questions about using one of the eight primary windings. I can't say with certainty but...
I would guess that unless the primaries are designed with additional inductance, you would rob the primaries of needed inductance to properly load your plates. If you haven't, check out K&K'S forum. Kevin Carter is a strong player in the audio world presently...very sharp guy who reps the Lundahl products...
How's your building experience?
Stuben
Yes, the feedback is coming from the secondary. It is another variation of CF. At the end of the day, we're trying to make a Pentode more linear using local Cathode feedback as opposed to global feedback else you can employ global feedback. I assume that is the reason you're interested in the CF windings. I can't imagine feedback that is not AC in nature.
If you run straight DC through your primaries, not happens in the secondaries. The AC element is what we're trying to amplify and reproduce accurately.
Stuben
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