Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: walkman on July 23, 2021, 11:14:45 pm
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Hi all.
Conjunctive filter for SE amp? Across Primary of OT or from plate to ground? Or will it make no difference for SE?
Do other things change the choice such as bias type or negative feedback?
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Conjunctive filter info please? - EL34 World :
https://el34world.com/Forum/index.php?topic=7620.0
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The Secret of Dr Z's Amp Mojo - RCA Conjunctive Filtering Design Guide;
https://www.tdpri.com/threads/the-secret-of-dr-zs-amp-mojo-rca-conjunctive-filtering-design-guide.310494/
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Thanks, I did read that post though as it was old did not want to resurrect a old topic.
In that thread there is an example given with the r + c across the primary , and a post by PRR stating what was often found in old radios was a corrective (conjunctive) but with the r component omitted.
I’ve seen many radio schematic with this and there is one in the thread as well.
The RCA 19 quoted in many places does not specify.
However there is an excerpt from Tremain's Audiocyclopedia that’s linked to in an 18watt post.
However the example shows that for PP the conjunctive filter arrange meant should be different depending on if negative need back is present.
There is no corresponding example for SE. Does this mean that NFB was rarely used in SE designs of the time and then not considered or otherwise the corrective filter arrangement is not affected by the presence or absence of NFB
(http://www.18watt.com/files/tremaine-corrective_filter.jpg)
https://www.18watt.com/viewtopic.php?t=4936 (https://www.18watt.com/viewtopic.php?t=4936)
In the SE amps I have with a corrective filter, I have the R+C from the plate (end of OT ) to ground rather than across the OT leads as I have seen in a few examples scattered across the web.
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plate (end of OT ) to ground
There is no corresponding example for SE.
that's what option d) shows :dontknow:
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In the SE amps I have with a corrective filter, I have the R+C from the plate (end of OT ) to ground rather than across the OT leads as I have seen in a few examples scattered across the web.
It's functionally the same thing. Ground is ground and B+ is AC ground due to the big filter caps.
This same "filter" is seen in many amps, makes no difference if SE or PP. A series cap and pot are connected from a tube plate to ground. It's called a treble bleed tone control.
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Thanks for all the reply’s I appreciate the clarification.👍
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> a post by PRR stating what was often found in old radios was a corrective (conjunctive)
Dunno what that guy was smoking.
> There is no corresponding example for SE.
Your fig d; also this Cadillac radio which is single-ended *transistor*.
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I had another look at the RCA19 and on p33 it does mention that for a beam power tube without negative feedback that an R+C filter can be put across the primaries.
However when NFB is present then it is important that this ‘tone control’ be moved outside of the loop. Please see the attached image (and forgive me if my paraphrasing or understanding is incorrect).
Again very appreciative for all the replies, and the inspiration to understand that this forum inspires.