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Ayab
Joined: Oct 27, 2015 Posts: 186 Location: London, UK
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Posted: Mon Mar 02, 2020 1:54 pm Post subject:
Substituting 6N2P tube in LMNC Safety Valve VCA |
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Got a couple of 6N2P tubes on eBay as a substitute for 12AX7/EEC83 to build LMNC Safety Valve Distorting VCA. But then I discovered the 6N2P has a different pin out to 12AX7/EEC83 (look before you leap, I know....).
The safety valve VCA stripboard design is attached. And also the schematic (which is difficult to read the numbers from and the schematic heater wiring differs from the stripboard, showing pin5 to ground and pin? to the 27r):
Also diagram of the pin out difference (from diy audio.com):
I’m planning to try using two 9v batteries in virtual ground configuration to test but am not really sure where to start with altering the connections for the tube.
I anyone understands tubes and can advise it would be great not to fry these lovely tubes and have a working distorting vca!
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Ayab
Joined: Oct 27, 2015 Posts: 186 Location: London, UK
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Posted: Tue Mar 03, 2020 2:07 am Post subject:
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Sam from Look Mum No Hands said it looks like it should be a direct replacement as pin 9 is not used. He is a great.
Will confirm when have built it |
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piedwagtail

Joined: Apr 15, 2006 Posts: 297 Location: shoreditch
Audio files: 3
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Posted: Sat Apr 11, 2020 9:06 am Post subject:
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The 6N2 is a 6.3V tube. You can't use 9V DC unless you use a 9 ohm 3W resistor (likely two 4.7ohms) to drop the voltage down at 300mA .Valves will burn through your batteries quickly, a dedicated 6V transformer supplying the filaments with AC would be more suitable; either ground as shown in the picture or use a humbucker pot in parallel. If you must have DC, then rectify and use a LDO 6V regulator.
Whichever way, it's not a drop in replacement; he uses the filaments in series ie. 12V when 9V isn't going to damage the filament. The 12xx7s can run at 6.3V with pins 4 and 5 joined for parallel operation. |
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Ayab
Joined: Oct 27, 2015 Posts: 186 Location: London, UK
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Posted: Sun Apr 12, 2020 12:54 pm Post subject:
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Thanks very much for the info piedwagtail
The circuit I am intending to use is for +12/-12V
So I need some hefty resistors! How would I wire them up? |
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Ayab
Joined: Oct 27, 2015 Posts: 186 Location: London, UK
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Posted: Tue Aug 18, 2020 2:29 pm Post subject:
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HOW TO ADAPT 6N2P to 12AX7
This describes a plug and socket solution where;
12AX7 = plug
6n2p = socket
12AX7 pins 1,2,3,4,6,7 and 8 go to 6n2p pins 1,2,3,4,6,7 and 8.
12AX7 pin 9 goes to 6n2p pin 5.
6n2p pin 9 links to 6n2p pin 8. (Cathode K2)
As the wise piedwagtail says the 6N2P is 6.3V so it cannot be used as a replacement for a 12AX7 when any voltage above that is being used.
I will see how it goes adapting the safety valve circuit to 6V |
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