Hammond 7247

[superhand]

I have some tubes that I took out of my old Hammond organ that is currently not working, and one of them is a Hammond branded 7247. Can I use this in place of a 12AX7 in a Vox AC4TV guitar amp? What will it do for my sound?

[Chuck H]

The 7247 is the same tube as a 12dw7 and wouldn't make for a very satisfying 12ax7 substitute. It's a dual triode (like other 12XX7 tubes) but one half is like a 12ax7 and the other is like a 12au7. A 12ax7 as a gain of 100 for both triodes. A 12au7 only has a gain of 20. So... A 12ax7 would be 100/100 and a 12dw7 (7247) would be 20/100.

It's not especially unsafe (there are minor exceptions) to use any 12XX7 type tube in another 12XX7 socket. The circuit will most likely not be ideal for the different tube type though.

Chuck

[superhand]

What about a 5751?

I have a 12AU7 in there now, which I kind of like, but I want more gain, but less than a 12AX7.

[Chuck H]

Then your on the right path. Go ahead and plug that 7247 in. It should have more gain than the 12au7. But IMHO if you want a treat, go find a 12ay7. One of my favorite tubes for tone. Just seem more "tubey" sounding and have a gain that falls right in between a 12au7 and a 12ax7. The only rub is that IIRC they draw a little more current than a 12ax7. I've never had a circuit fail because of it, but I suppose it could burn up a preamp resistor or something minor like that if the amp is built with 1/4 watt resistors or something.

Chuck