How do i convert this 12FQ8 tube pre amp for 12AX7 use ?
http://www.instructables.com/files/orig/F7C/AK28/FVW22RXO/F7CAK28FVW22RXO.pdf
http://www.instructables.com/files/orig/F7C/AK28/FVW22RXO/F7CAK28FVW22RXO.pdf
You cant. Sorry but a 12ax7 wont work at 12-16v b+, end of story.
Also the 12fq8 is a very odd ball tube. Its got 4 plates instead of 2 like the 12ax7, and it has a shared cathode instead of 2 like the 12ax7.
If you can give us some info we can pick you out a better design. AKA you are cheap and just have 12ax7's running around, do you need it to work at 12volts, stuff like that.
Have you tried the other 2 variations that use normal tubes?
http://www.diystompboxes.com/smfforum/index.php?topic=63479.0
http://www.dogstar.dantimax.dk/tubestuf/mctube.htm even uses 12ax7. Its power supply is a little funky but can easily be made normal.
Also the 12fq8 is a very odd ball tube. Its got 4 plates instead of 2 like the 12ax7, and it has a shared cathode instead of 2 like the 12ax7.
If you can give us some info we can pick you out a better design. AKA you are cheap and just have 12ax7's running around, do you need it to work at 12volts, stuff like that.
Have you tried the other 2 variations that use normal tubes?
http://www.diystompboxes.com/smfforum/index.php?topic=63479.0
http://www.dogstar.dantimax.dk/tubestuf/mctube.htm even uses 12ax7. Its power supply is a little funky but can easily be made normal.
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that oddball tube 12FQ8 are only stocked as NOS tubes , 50$ ( oh yeah , i live in singapore )
And , the only cheap option is 12AX7 , no , i'm beginner and have no tubes at all .
I sort of saw the diystompboxes , and didn't give a , nevermind .
What sort of info are you looking for ?
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Big risk ?
I don't know , if anything goes wrong , 6.50 down the drain .
I'm a student , so no funding at all . ( Unless somebody asks me to produce one more
)Since i have no clue what you are after. a 12ax7 has a gain of 100 and will never work at low voltages. I have no clue what gain the 12fq8 is.
try a 12au7, they are $5 or so with a gain of 17 and is the best shot at 12 volts just like your circuit.
http://www.nj7p.org/Tube4.php?tube=12AU7
http://www.netads.com/~meo/Guitar/Tubes/dual-triodes.pl
now lets rearrange the pins so it works with the circuit.
12FQ8.
1 becomes pin 1 on 12au7
2 becomes pin 2 on 12au7
2 becomes pin 3 on 12au7
3 becomes pin 1 on 12au7
4 becomes pin 4 on 12au7
5 becomes pin 5 on 12au7
6 becomes pin 6 on 12au7
7 becomes pin 7 on 12au7
8 becomes pin 6 on 12au7
9 becomes pin 8 on 12au7
9 becomes pin 3 on 12au7
pin 9 is not used on the 12au7 or 12ax7 when you are using 12v heaters. If you are still hell bent on a 12ax7 then this pinout will work too.
As far as playing 20 questions. We now know you are a beginner,not in the usa, and a student with a low budget. Next question, what do you want to do with this? Is this for a battery powered guitar pickup box or something?
try a 12au7, they are $5 or so with a gain of 17 and is the best shot at 12 volts just like your circuit.
http://www.nj7p.org/Tube4.php?tube=12AU7
http://www.netads.com/~meo/Guitar/Tubes/dual-triodes.pl
now lets rearrange the pins so it works with the circuit.
12FQ8.
1 becomes pin 1 on 12au7
2 becomes pin 2 on 12au7
2 becomes pin 3 on 12au7
3 becomes pin 1 on 12au7
4 becomes pin 4 on 12au7
5 becomes pin 5 on 12au7
6 becomes pin 6 on 12au7
7 becomes pin 7 on 12au7
8 becomes pin 6 on 12au7
9 becomes pin 8 on 12au7
9 becomes pin 3 on 12au7
pin 9 is not used on the 12au7 or 12ax7 when you are using 12v heaters. If you are still hell bent on a 12ax7 then this pinout will work too.
As far as playing 20 questions. We now know you are a beginner,not in the usa, and a student with a low budget. Next question, what do you want to do with this? Is this for a battery powered guitar pickup box or something?
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The 12FQ8 has a gain of 95, and by all rights probably shouldn't work at such low plate voltages either. The RCA datasheets show operating conditions with "normal" plate voltages around 250.
If you go find and read the original "ValveLitZer" article, it says the "designer" fully expected it not to work, but he had a bunch of 12FQ8 and wanted to mess with them. It's not intended to pass clean audio, but rather to add a lot of "character".
The ValveLiTzer: Low-voltage Tube Booster
Someone even asked (back in 2009) whether it works with a 12AX7. Apparently the author answered the question, but didn't post the answer publicly.
12FQ8 is very similar to 12AX7 when both anodes are connected together.
See here: http://www.mif.pg.gda.pl/homepages/frank/sheets/093/1/12FQ8.pdf
So, if 12FQ8 has been suitable for the circuit shown, then 12AX7 will definitely work better with same component values than 12AU7.
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