Foreplay 1 to buffer

RPMac · 2644

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Offline RPMac

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on: March 21, 2011, 09:39:44 AM
Would it be possible to convert an extra FP1 to John Broskie's Aikido Cathode Follower version 2? I will use it as a tube buffer between my FPIII and squeezebox.

http://www.tubecad.com/2011/01/blog0198.htm

I have no design ability, but the problem I see is that his circuit uses a center tap power transformer for the bipolar supply. Can the stock FP transformer be used to get a bipolar supply?
I would want to use 12au7 tubes because I have them.
« Last Edit: March 21, 2011, 09:49:24 AM by RPMac »


Offline RPMac

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Reply #1 on: March 22, 2011, 05:03:25 AM
If I wire two stock FP1 PT secondaries in series, will it work as a 125-0-125 center tap?


Offline Grainger49

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Reply #2 on: March 22, 2011, 05:15:43 AM
I expect that the primaries, properly phased, in parallel and the secondaries, properly phased, in series will easily give 125V-0V-125V CT output at 15mA.

If you get one primary out of phase then the output will also be out of phase.

Sorry if I am being to elementary.


Offline RPMac

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Reply #3 on: March 22, 2011, 07:17:36 AM
Grainger, I don't think you can get too elementary for me.

I thought there might be phase issues with two transformers. Will I be able to find the proper phase by trial and error measuring the secondary voltage until I get 125V-0-125V? The two filament winding will allow me to buy one of John's regulated power supplies to upgrade my squeezebox from its wallwart.


Offline Grainger49

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Reply #4 on: March 22, 2011, 07:31:38 AM
Robert,

If you parallel the primaries you can twist any two, one from each transformer and read the remaining two.  You will get zero or near zero if they are out of phase.  Otherwise you will read 240V with the twisted two being your CT.

Yeah!  The benefit is double the heater current.  Depending on how many tubes you want to drive you might even have enough left over for DC.  Though it will be a little low on voltage.


Offline 2wo

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Reply #5 on: March 22, 2011, 01:36:10 PM
If you have 2 transformers, you can build 2 supply's and not worry about transformer phase.

Say you need +100V & -100V. Build 2, 100V supply's and connect the "ground" side of one to the + side of the other, call this connection point the circuit "ground" or return might be the better term. From here you have +100 looking up and -100 looking down...John     

John S.

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