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Old 26th August 2009, 02:38 AM   #1
cjkpkg is offline cjkpkg  United States
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Default phono stage woes...

I made a PCB for the RJM phono stage to the attached schematic. I finally hooked everything up tonight and I get nothing, nada, bubkus...

I plugged the TT directly into the aikido and actually got a little noise with the volume all the way up. Plugged it back into the phono stage and nothing...

I am getting 237V B+, 87V at the plates, and about 2.3V off the cathodes. I followed all recommended values for caps and resistors. The one wierd thing is that one tube is drawing 7.2V for the heaters and the other one 5.6V. When I switch positions the wierd voltage follows the tube.

Attached is my PCB layout too...
1=plate2
2=grid2
3=cathode2
4=heater
5=heater
6=plate1
7=grid1
8=cathode1
9=IS

I looked over the PCB layout ad nauseum...please let me know if I am missing something truly obvious...
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Old 26th August 2009, 02:48 AM   #2
Salas is online now Salas  Greece
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What kind of cartridge you use?
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Old 26th August 2009, 02:53 AM   #3
cjkpkg is offline cjkpkg  United States
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An Audio Technica AT15SA - MM type...
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Old 26th August 2009, 03:06 AM   #4
Salas is online now Salas  Greece
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Can you measure any DC voltage across the phono input? If its there, it shouldn't. You would need to block with a capacitor.
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Old 26th August 2009, 03:12 AM   #5
cjkpkg is offline cjkpkg  United States
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Should I measure idle or put a record on and measure?
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Old 26th August 2009, 03:14 AM   #6
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Looking over the PC layout I don't see anything obviously wrong. However, since your tube filaments are in series and the voltages are not equal, the tubes filaments are drawing unequal currents. This causes unequal voltage across them. At least one of the tubes is defective. Maybe both. This could also explain the lack of sound. What tubes are you using? Better try some good quality tubes and 86 that imported garbage.
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Old 26th August 2009, 03:17 AM   #7
Salas is online now Salas  Greece
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Quote:
Originally Posted by cjkpkg View Post
Should I measure idle or put a record on and measure?
Just measure the input without anything connected. I wanna know if the grid leaks on input load. DC there is not welcome. It can bias up the cart or even worse... Change the tube if you can find any.
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Old 26th August 2009, 03:24 AM   #8
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Quote:
Originally Posted by cjkpkg View Post
An Audio Technica AT15SA - MM type...
Great cart.
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Old 26th August 2009, 04:07 AM   #9
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Quote:
Originally Posted by HollowState View Post
...since your tube filaments are in series and the voltages are not equal, the tubes filaments are drawing unequal currents.
Magic filaments, or maybe they just would if they weren't in series?
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Old 26th August 2009, 05:20 AM   #10
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I think your tubes are upside down.

Quote:
Originally Posted by Salas View Post
Can you measure any DC voltage across the phono input? If its there, it shouldn't. You would need to block with a capacitor.
Why would there be DC on the grid?
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