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Old 7th April 2013, 09:47 AM   #1
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Default NEED ADVICE ON THIS SCHEMATIC AND WILL IT WOFK

Hi All, I am working on a Project with another Member, and we are looking to build this amplifier. We are using the Old Transformers from a Wards Console SE amplifier. The notation on the Schematic shows the output transformers at 2.5k ohms, But this was pasted from another website. Our output transformers are 500 ohms Primary, 1 ohm secondary resistance. Now, looking at the Power Supply, the choke I have no Idea how to size it according to what's there, much less if it's in the right place. I need some guidance in coming up with a value. If you know of a value you would use please let me know, that would be appreciated. The other point is where would I hook up the Bias pot and Meter for each channel, If I were to do TubeCad's Fixed Bias circuit, I would need a -36v power supply correct? I am not sure of the voltages if they are correct, I was going by the Wards Schematic for that! Any advice on this amplifier would be appreciated VERY much!!! Lydia
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Old 7th April 2013, 10:46 AM   #2
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The 6CA4/EZ81 is good for 150 mA. of B+. Is that enough for 2 channels?

Unless you use current regulated DC to energize the 6B4 filaments, you are going to be driven insane by hum. If you want AC heating, use 2A3s.
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Old 7th April 2013, 11:46 AM   #3
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Quote:
Originally Posted by pianolydia View Post
Our output transformers are 500 ohms Primary, 1 ohm secondary resistance.
Just a note: if these are DC multimeter resistance measurements, they are NOT the same as the AC impedance measurements and they do NOT give any indication of the transformer ratio.

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Old 7th April 2013, 01:45 PM   #4
MelB is offline MelB  Canada
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If you are going to have that 1K resistor in the B+ I would add in another cap if you have room then you could use a much smaller choke and get most likely even less ripple on your B+. Are you sure you want a 1K resistor in your B+? Seems a terrible waste of power.
Example if keeping the 1K resistor: 6CA4 => 33uF => 2H choke(or less) => 33uF => 1K resistor => 47uF => output trans.
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Old 7th April 2013, 02:04 PM   #5
MelB is offline MelB  Canada
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If you have the choke and need a value for it, as Eli said it should be rated for about 150mA, look on this chart and check against the size/resistance of choke you have there. I would think you should get pretty close.
Hammond Mfg. - D.C. Filter Chokes - (153 - 159 Series)
Also if you are using cathode bias I would try to get as much voltage as possible to the anode of the 6B4G from your current power supply.
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