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Author Topic: Astatic D-104 with 1 volt on Mic  (Read 878 times)
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n8fvj
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« on: August 26, 2023, 09:18:03 PM »

The unamplified D-104 as used on a Johnson Ranger sees 1 volt on the mic from 12AX7 grid thru a 4.7K resistor. Does the D-104 element have a blocking capacitor installed? If not does not will 1 volt affect the mic?

I can find 100s of amplified D-104 schematics but not one unamplified schematic.
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n8fvj
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« Reply #1 on: August 27, 2023, 08:57:44 AM »

No replies. I will install a coupling cap in microphone base to remove that 1 volt.
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KB2WIG
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« Reply #2 on: August 27, 2023, 12:40:13 PM »



My unamped d10-4 has a schematic inside the bottom plate... not at home, so I can't give yew a definitive answer.

KLC
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Pete, WA2CWA
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« Reply #3 on: August 27, 2023, 02:48:17 PM »

Pin 2 of the 12AX7 should have zero volts on it from original design. See the partial schematic.


* johnRanger_mic_inp.jpg (88.16 KB, 904x600 - viewed 67 times.)
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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
Pete, WA2CWA
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« Reply #4 on: August 27, 2023, 03:06:34 PM »

UNAMPLIFIED ASTATIC D-104 SCHEMATIC
Easy to find - see below
The microphone cartridge does not have any series "blocking-type  capacitor" in the lead.
 


* Astatic_D104plain.jpg (127.35 KB, 1015x1014 - viewed 61 times.)
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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
n8fvj
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« Reply #5 on: August 27, 2023, 03:50:10 PM »

Thanks Pete.
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DMOD
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« Reply #6 on: August 27, 2023, 07:54:20 PM »

No replies. I will install a coupling cap in microphone base to remove that 1 volt.

No need to if you understand the schematics posted here in post #12 and 16  and following:

http://amfone.net/Amforum/index.php?topic=48171.0

What is your grid resistance? The higher the grid resistance the greater the grid-leak voltage; basic tube theory.
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