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Old 13th November 2012, 09:03 PM   #1
aldovan is offline aldovan  Brazil
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Default 47 pentode...fabulous sound !!!!

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I love the triode sound !
But I did some experiments with the old 47 pentode in pentode mode, single ended class A and...WOW !!!
The sound is very nice, very detailed, with good bass and treble and a wonderful medium response, the voice and rhythms are very clear !
I use a Tesla E180F in triode mode as pre amplifier and a Edcor transformer in output. My experimental speaker is a cardboard open baffle, with a Trusonic FR80 speaker and a Foster horn.
Watch the video, sorry for the mess in my prototype and the bad video ... but my free time is small!

Raytheon 47 pentode in Single ended mode - YouTube

Aldovan
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Old 13th November 2012, 09:09 PM   #2
cotdt is offline cotdt  United States
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very nice! thanks for sharing
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Old 13th November 2012, 09:25 PM   #3
aldovan is offline aldovan  Brazil
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Originally Posted by cotdt View Post
very nice! thanks for sharing
Thanks !
This is my basic project. It use a 330V power supply and I do not test, yet.
The prototype is working with a 280V power supply.
The schematic is very simple and easy for make.


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Old 13th November 2012, 09:47 PM   #4
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What is the purpose of 1k2 resistor in series with primary of OPT? Assuming 6mA grid current in any condition, the drop would be ca. 30V, not 50V. If you want 250V, you should at least use voltage divider with a bypass cap or better some voltage regulator.
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Old 13th November 2012, 09:57 PM   #5
aldovan is offline aldovan  Brazil
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Default resistor

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Originally Posted by yagoolar View Post
What is the purpose of 1k2 resistor in series with primary of OPT?
Only reduce the plate voltage.
The 47 have a maximum voltage of 250V.
This resistor do not is necessary if you use the correct plate voltage.
But the 6DQ3 rectifier have a low drop voltage.
The rectification is by solid state diodes and the 6DQ3 is used for a soft high voltage start, only.

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Old 13th November 2012, 10:00 PM   #6
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So you should put it between 47uF and the OPT bypassed with another cap. Use PSUD2 to choose proper values based on simulations. You will have LCRC filter.
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Old 13th November 2012, 10:04 PM   #7
aldovan is offline aldovan  Brazil
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Originally Posted by yagoolar View Post
What is the purpose of 1k2 resistor in series with primary of OPT? Assuming 6mA grid current in any condition, the drop would be ca. 30V, not 50V. If you want 250V, you should at least use voltage divider with a bypass cap or better some voltage regulator.
Yes, the drop is 30V, you is correct.
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Old 13th November 2012, 10:06 PM   #8
aldovan is offline aldovan  Brazil
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Originally Posted by yagoolar View Post
So you should put it between 47uF and the OPT bypassed with another cap. Use PSUD2 to choose proper values based on simulations. You will have LCRC filter.
Thanks for the informations, I will use the simulator.
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Old 13th November 2012, 10:17 PM   #9
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Read about triode-strapped pentode also. I assume you wanted pentode mode, i.e. Ug2=250V
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Old 13th November 2012, 11:21 PM   #10
aldovan is offline aldovan  Brazil
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Originally Posted by yagoolar View Post
Read about triode-strapped pentode also. I assume you wanted pentode mode, i.e. Ug2=250V

For triode strapped I prefer the 46.

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