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Old 9th February 2004, 10:04 AM   #1
MIKET is offline MIKET  United States
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Default Just finished my new 300B amp

in testing phase now
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Old 9th February 2004, 10:05 AM   #2
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Default Power supply

see below:
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Old 9th February 2004, 10:07 AM   #3
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Default Timer Board

see below:
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Old 9th February 2004, 10:23 AM   #4
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Default Power Supply Transformer Details

Transformer is from Toroid Corporation of Maryland
Model Number is 401.040 400VA transformer kit, wininding details to follow soon.
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Old 9th February 2004, 10:34 AM   #5
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Why the 10 zenner diodes in the anode circuit of the input valve??
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Old 9th February 2004, 11:20 AM   #6
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Default Zener Question

To lower the b+ not to excede the rating on the depletion mode FET. I have also updated the schematic to show the bias monitor for the output tube. Set the output tube bias to 60mA.
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Old 9th February 2004, 11:21 AM   #7
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Default Schematic Below

1V=1mA
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Old 9th February 2004, 11:23 AM   #8
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Default Re: Zener Question

Quote:
Originally posted by MIKET
To lower the b+ not to excede the rating on the depletion mode FET.
But a resistor will do the same with less noise and increasing the output impedance of the current source...

Zeners are one of the most noisy component in electronics...they produce lots of white noise.

Just one sugestion...
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Old 9th February 2004, 11:31 AM   #9
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Default Resistor sub for Zener

I will give it a try and let you know what improvement if any is noted, I will keep you posted. I will try a6K 10W resistor for starters.
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Old 9th February 2004, 11:36 AM   #10
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Default Re: Resistor sub for Zener

Quote:
Originally posted by MIKET
I will give it a try and let you know what improvement if any is noted, I will keep you posted. I will try a6K 10W resistor for starters.
Another point in favor of the resistor is that the mosfet have great parasitics capacitances that shunt power suplly noise to the anode of the input tube...and the resistor help to isolate this parasitic path...

Good luck and keep in touch!!
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