Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jeff on July 24, 2024, 06:44:43 pm

Title: ½ 12AX7, ½ 12AU7 in one tube.
Post by: jeff on July 24, 2024, 06:44:43 pm

Hi guys,
I'm looking for a 9pin tube that is ½12AX7 ½12AU7.
I think 7247 is one, are there others?
Don't care which side is which, or if pinout is scrambled(vs 12AX7) new build so any 9pin AX/AU's you know of.
Thanks.
Jeff

Title: Re: ½ 12AX7, ½ 12AU7 in one tube.
Post by: Jonas on July 24, 2024, 07:00:58 pm

Yes 7247 or 12DW7 is what you are looking for.
pins 1, 2, and 3 are the AU half (amplification factor 20)
pins 6, 7, and 8 are the AX half (amplification factor 100)

JJ makes the ECC832 which is also a dissimilar dual triode but the pin out is reversed in that 6, 7, and 8 are the AU half

There are other dissimilar dual triode but I don't recall one in which the amplification factor difference between the two halves were as "dissimilar" to the 7247

hope this helps.... 

Title: Re: ½ 12AX7, ½ 12AU7 in one tube.
Post by: Jonas on July 24, 2024, 07:04:42 pm

Here you go Jeff!

https://www.angelfire.com/electronic/funwithtubes/duo_dis_triodes.html

Title: Re: ½ 12AX7, ½ 12AU7 in one tube.
Post by: jeff on July 24, 2024, 07:23:47 pm

Thanks

Title: Re: ½ 12AX7, ½ 12AU7 in one tube.
Post by: stratomaster on July 25, 2024, 08:26:58 pm

Quote from: Jonas on July 24, 2024, 07:00:58 pm

JJ makes the ECC832 which is also a dissimilar dual triode but the pin out is reversed in that 6, 7, and 8 are the AU half

The JJ ECC832 and ECC823 both exist. They are mirror images of each other. I want to say (from memory) the former is equivalent to the 12DW7, but it would be best to consult the datasheet prior to purchase.