aikido voltage swing

Bill*B · 8th August 2005, 08:15 PM

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.

agent.5 · 8th August 2005, 09:09 PM

From what I read, the gain is 1/2 of the mu of the front stage.

Bill*B · 9th August 2005, 03:38 AM

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.

agent.5 · 9th August 2005, 03:53 AM

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.

heater · 9th August 2005, 06:16 AM

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.

Bill*B · 9th August 2005, 11:13 AM

Thanks, all. I appreciate your input.

Bill*B · 9th August 2005, 10:04 PM

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.

dave dove · 9th August 2005, 10:47 PM

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

Bill*B · 10th August 2005, 12:22 AM

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!

8th August 2005, 08:15 PM	#1
Bill*B diyAudio Member Join Date: Sep 2004 Location: tampa, florida, USA	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.

9th August 2005, 06:16 AM	#5
heater diyAudio Member Join Date: Jul 2004 Location: Helsinki	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. __________________ For me the past is not over yet.

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8th August 2005, 09:09 PM	#2
agent.5 diyAudio Member Join Date: Aug 2003 Location: San Francisco, CA	From what I read, the gain is 1/2 of the mu of the front stage.

9th August 2005, 03:38 AM	#3
Bill*B diyAudio Member Join Date: Sep 2004 Location: tampa, florida, USA	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.

9th August 2005, 03:53 AM	#4
agent.5 diyAudio Member Join Date: Aug 2003 Location: San Francisco, CA	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.

9th August 2005, 11:13 AM	#6
Bill*B diyAudio Member Join Date: Sep 2004 Location: tampa, florida, USA	Thanks, all. I appreciate your input.

9th August 2005, 10:04 PM	#7
Bill*B diyAudio Member Join Date: Sep 2004 Location: tampa, florida, USA	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.

9th August 2005, 10:47 PM	#8
dave dove diyAudio Member Join Date: Mar 2005 Location: mid wales	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

10th August 2005, 12:22 AM	#9
Bill*B diyAudio Member Join Date: Sep 2004 Location: tampa, florida, USA	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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