Elevate center tap or send to ground?

Blueslover88

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In the RR2104 it shows the artificial center tap bring elevated. Do I need to do this if I have an actual center tap or just solder to ground lug?
 

SerpentRuss

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Any amp build with a long tail pair phase inverter and/or a cathode follower will benefit from an elevated heater ground. The voltage divider used to get the reference voltage will also act as a bleed for the power supply capacitors.
 

Blueslover88

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Any amp build with a long tail pair phase inverter and/or a cathode follower will benefit from an elevated heater ground. The voltage divider used to get the reference voltage will also act as a bleed for the power supply capacitors.
So I can just land the center tap at the top of the 180k voltage divedr/bleeder right?
 

cottontails1959

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Per Blencowe ... "The DC voltage is applied to ... whatever reference connection the heater supply would normally have. The elevation voltage can be taken from a potential divider across the HT (it doesn't matter where you position the divider), and an elevation voltage around 30 to 60V is typical." and "The elevation voltage should be decoupled/smoothed with an arbitrarily large capacitor (C1), say 10uF or more." IIRC, if your transformer has a heater center tap, use that - no need for an artificial center tap. You land the CT in the "center" of the voltage divider ... the junction of R1:R2 ... for example, if the divider is 180K:39K with 340V, the heater elevation is 340*(39/(39+180)) = 60.5V. However, as @dan40 asks, a schematic or layout drawing will help.
 

SerpentRuss

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Here is an example. You want the total resistance to be fairly large, but not too large. Just pick your resistors based on your B+ voltage and mind the wattages so they can handle the power.
 

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Blueslover88

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Is this an actual divider that is set up to give the correct voltage or is it simply a bleeder resistor? Do you have a schematic or layout drawing of this?
 

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Blueslover88

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Per Blencowe ... "The DC voltage is applied to ... whatever reference connection the heater supply would normally have. The elevation voltage can be taken from a potential divider across the HT (it doesn't matter where you position the divider), and an elevation voltage around 30 to 60V is typical." and "The elevation voltage should be decoupled/smoothed with an arbitrarily large capacitor (C1), say 10uF or more." IIRC, if your transformer has a heater center tap, use that - no need for an artificial center tap. You land the CT in the "center" of the voltage divider ... the junction of R1:R2 ... for example, if the divider is 180K:39K with 340V, the heater elevation is 340*(39/(39+180)) = 60.5V. However, as @dan40 asks, a schematic or layout drawing will help.
I posted below it's Rob's jcm 800 ef80 build
 

Blueslover88

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Yep...just attach your CT to the same turret that the green/yellow wire is attached to in the layout.
Here is the finished product. Not as clean as I'd like but it leaves something to do when I get bored. I may run the leads under the board at some point but SUPER happy with the sound
 

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dan40

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Congratulations on a successful build! I have a stash of old EF80's and I have been contemplating building this circuit myself. It's down to either this one or the micro Bassman.
 

Blueslover88

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Congratulations on a successful build! I have a stash of old EF80's and I have been contemplating building this circuit myself. It's down to either this one or the micro Bassman.
Thanks Dan. I built a KLD 5e3 kit first. Then I built a micro 5e3 with 12au7 power tube. I had leftover parts so I built the 5e3 with ef80. I didn't care much for the ef80 5e3 so I stole some of it's components to make this jcm800 and boy am I glad I did!
 




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