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Old 8th August 2005, 08:15 PM   #1
Bill*B is offline Bill*B  United States
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Default aikido voltage swing

I'm having trouble calculating how much output swing the Aikido setup produces. Anybody who has built one, I'd be grateful for your comments. I plan to use a 12AH7 (medium mu twin triode) at about 300V B+, with 1K resistors (should give around 7 ma), but need a clean 10V RMS swing into a 15K ohm load. Regards, Bill.
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Old 8th August 2005, 09:09 PM   #2
agent.5 is offline agent.5  United States
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From what I read, the gain is 1/2 of the mu of the front stage.
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Old 9th August 2005, 03:38 AM   #3
Bill*B is offline Bill*B  United States
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Yes, that's what I'd expect the totem pole to do - and according to Tube CAD it (the input stage) will provide a nice + or - 70V swing into the cathode follower. I'm just worried about the tiny cathode resistor in the cathode follower output stage. When I run the numbers in the current sourced cathode follower model provided by Tube CAD (not a exact match - no place for the upper resistor in that simulation) it give me a very limited voltage swing of only 7 or 8 volts. Should be adequate to drive an amp which needs prehaps a half volt swing, but I wanted to drive the primary of a 4:1 stepdown transformer.
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Old 9th August 2005, 03:53 AM   #4
agent.5 is offline agent.5  United States
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I think the output impedance of this circuit is pretty low. So, why do you need a step-down transformer? Maybe just use a 1:1 output transformer, if you must.
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Old 9th August 2005, 06:16 AM   #5
heater is offline heater  Finland
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No idea what the TubeCAD model looks like you are using looks like. Are you taking the output from the right place ?

The anode of the lower right tube in aikido will follow the first stage to within a few volts. Easily swinging 70 to 100 volts.

Don't forget is the lower right tube plus its cathode resistor that are the load for the top right tube cathode follower.
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Old 9th August 2005, 11:13 AM   #6
Bill*B is offline Bill*B  United States
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Thanks, all. I appreciate your input.
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Old 9th August 2005, 10:04 PM   #7
Bill*B is offline Bill*B  United States
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Just an update for all who are interested in the Aikido. The designer was kind enough to answer my concern and reports that both in SPICE and reality he finds a clean 80V output swing. Regards, Bill.
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Old 9th August 2005, 10:47 PM   #8
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also

i asked JB about 5:1 output transformer
he said i'd still need a coupling cap
though smaller

i did try it
but psu is in same box
i got induced hum
and no improvement

dave dove
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Old 10th August 2005, 12:22 AM   #9
Bill*B is offline Bill*B  United States
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Thanks for the report - as output Z should be only 400 ohms or so without the transformer, there's really no need for me to use one - I just was looking for a place to play with a pair I have on hand.
I'm building the Aikido because the simple little CF I just built has an audible hum. I'm sure that's because I cobbed it together with little attention to the physical layout - will plan (and shield) a little better this time!
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