Plate chokes
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 31st December 2009, 10:54 AM #1 rsumperl   diyAudio Member     Join Date: Oct 2009 Location: Cascade, Idaho Plate chokes Greetings everyone and a happy new year! What are the advantages to using a plate choke vs a resistor in the plate circuit? Besides there being more voltage at the plate, are there any other advantages? How does one choose the size (# of henries) for the choke? Thanks, Ray
 31st December 2009, 11:19 AM #2 SY   On Hiatus     Join Date: Oct 2002 Location: Chicagoland For a given B+, a plate choke will nearly double the possible voltage swing. In some situations, that's important. Additionally, the choke provides a higher load impedance at high frequencies than a resistor, but not as much as a good constant current source (CCS). Inductance is a bit trickier to calculate, but as a rule of thumb, choose an impedance at 5-10 times the tube's effective plate resistance. Using the inductance formula (|Z| = 2pi*f*L), calculate the required inductance at the lowest frequency of interest. This will probably give a larger value than you need, but will guarantee that the plate loading doesn't move around much as you go down in frequency. For me, I would never use a plate choke unless I absolutely needed the swing- they're large, expensive, and subject to all sorts of unpleasant non-ideal behavior. A CCS or gyrator in the plate circuit will outperform any choke in all areas except swing. __________________ "You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
 31st December 2009, 12:50 PM #3 tvrgeek   diyAudio Member   Join Date: Dec 2009 Location: Md Sy, Sorry to butt in, newbee to tubes. I thought the CCS was normally a replacement for the cathode resistor. Or does it not matter? Can you point me to a sketch of using a gryator in the plate? I have been collecting schematics to understand the why's of tube implementation and have not run into this idea.
 31st December 2009, 01:43 PM #4 SY   On Hiatus     Join Date: Oct 2002 Location: Chicagoland A tubee newbee? Cool, than I get to flog Morgan Jones's book one more time- get yourself a copy of "Valve Amplifiers" post-haste. It's the introduction I wish I'd had when I got started with tubes back in the day when LBJ was in the White House. MJ covers these topics, and most everything else you'd want to know about tube design, in exquisite detail. In any case... a CCS in the plate circuit acts as (essentially) an infinite plate load, which runs the tube at maximum gain (mu) and minimum distortion (horizontal load line). The choke is an approximation to this at frequencies where its impedance is >> plate resistance. In a cathode circuit, the extremely high Z drops the gain of the stage to unity, which is fine for a cathode follower, but exactly the opposite of what you'd want for a gain stage. If you do a forum search for "gyrator" and posts by "Wavebourn," you'll find some very clever circuits. __________________ "You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
 31st December 2009, 01:46 PM #5 Zen Mod   Official Court Jester diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain @SY btw. where is Kwayzee Russian these days ? ( I don't have anything to add to rest of your replies ) __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
 31st December 2009, 01:49 PM #6 SY   On Hiatus     Join Date: Oct 2002 Location: Chicagoland Probably working too hard. __________________ "You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
 31st December 2009, 03:45 PM #7 tvrgeek   diyAudio Member   Join Date: Dec 2009 Location: Md "Double plus thanks" Planning on Jones as soon as I finish fighting my way through Finch. My calc is a bit rusty. What is fun is I find myself going for my Dad's old Terman handbook from when he went to school. They did not teach tubes when I went through. Of course, if we add solid state power supplies, CCS's, then maybe an integrated ss phase splitter, pretty soon we are ready for FET outputs and no longer have a tube amp!
 31st December 2009, 03:54 PM #8 tvrgeek   diyAudio Member   Join Date: Dec 2009 Location: Md OK, OK, ordered both of his books. Looking aththe TOC, his building looks good as I have observed execution can be as important as the circuit. VTL comes to mind. Supurb results with ordinary topology.
 31st December 2009, 04:08 PM #9 SY   On Hiatus     Join Date: Oct 2002 Location: Chicagoland You'll not regret that purchase. MJ is buggy about getting the build right (when viewing my construction efforts, he generally rolls his eyes heavenward). The cover item on VA (the Crystal Palace amplifier) is a model of optimizing very conventional topologies and attention to the details of engineering. BTW, where in Maryland are you? (UMBC, class of '77) __________________ "You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
 31st December 2009, 05:36 PM #10 tvrgeek   diyAudio Member   Join Date: Dec 2009 Location: Md Bowie. LHS class of 73.

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