12DW7 - Good for Anything?

[boots]

I scored some 12DW7's (aka 7247) - they appear to be Mullards with the Blackburn code. They are OEM branded.

I understand it is a dissimilar dual triode. Is it of any use in a guitar amp? I wondered about using it in something like a amp that has two inputs (such as mic and instrument - like in some of the old Fender Tweeds).

I usually find myself using only one of the inputs anyway. Would it make sense to pop in a 12DW7 and just use the input with the "hot" triode? I imagine it would sound sweet, like a Mullard AX7.

Would it make sense to burn through DW7's and save my good AX7's? Does anybody have any use for the DW7's? They are sweet looking tubes, but I am not aware of any guitar amps that use them.

[cbass]

Nope totally worthless send emto me and I'll dispose of them.

I've heard ofpeopleusing them in princetons but you have to swithch the wiring around at the socket so the au7 side is on the PI

[cbass]

Also might be good for amps like the express with an unused triode

[HeeBGB]

Should be a pretty desireable tube. Used in vintage Ampeg's. Specifically SVT's. Probably worth a few bucks if you don't need them

[Phil_S]

Those aren't good for anything. Very dangerous tubes. Send them to me for expert disposal

They are good for many things. It is half 12AX7 and half 12AU7. For example, the X makes a regular gain stage and the U can be used for a reverb driver or a split load (cathodyne/concertina) PI. Not too long ago, someone a good schematic on cascading 12AU7's https://tubeamparchive.com/viewtopic.php?t=19498

You could even use the X halves for gain and use a pair of U halves for a LTP. Lot's of possibilities.

[JazzGuitarGimp]

If you do repair work, you might have a use for a couple of them. I just had an Ampeg VT-22 in for repair. It has a 12DW7.

[selloutrr]

Correct it's a very common tube in Ampeg amps built from '60-'81. Before the tube went out of mass production. They are some what desirable. About the same value as a good AT7. Due to the tube being discontinued simple modifications to use the 12AX7 have allowed the vintage amps to stay operational. In the last decade, JJ/Tesla and new sensor have both brought the DW7 back into production. It was a push from Groove Tubes to keep vintage amps operational.

[JazzGuitarGimp]

Correct it's a very common tube in Ampeg amps built from '60-'81. Before the tube went out of mass production. They are some what desirable. About the same value as a good AT7. Due to the tube being discontinued simple modifications to use the 12AX7 have allowed the vintage amps to stay operational. In the last decade, JJ/Tesla and new sensor have both brought the DW7 back into production. It was a push from Groove Tubes to keep vintage amps operational.

So, what you're saying is: Groove Tubes is good for something other than bending us over and robbing us of our [financial] virginity?

[MCK]

Nice find! I have an amp that uses them. Could be interested in a nice NOS if you decide to put them on the market.

[Jack Hester]

The high-mu side (pins 6,7, & 8 ) can be used as a high gain stage like that of a 12AX7. The medium-mu side (pins 1,2, & 3 ) is the workhorse, used for cathode follwers, PI's, or a medium gain stage. It can carry quite a bit more current than the high-mu side, which is why it's particularly good for a CF.

Jack

[Phil_S]

If they test well into the good range, even close to new, you can get $15-$20 each on eBait. If you don't have test results to sell, more like $10.

[tubeswell]

Great for an FX loop with the AU side as a CF buffer driving the loop and the AX side as the recovery (inverting) stage.

Or as a cascode with the AU side as the transconductance stage (the bottom of the totem pole) and the AX side as the other stage.

Or (if you elevate the heaters to about 50V or so) for a pair with the AX triode as a straightforward inverting stage and the AU triode as a CF driving a heavy load like a TMB tone stack, or a driver-pair for a 'high power' tube like a KT88 in a SE amp, or as or as a driver/cathodyne pair in a PP amp, or as an LFO tremolo driver, with the AX side as the LFO and the AU side as the buffer CF stage

Or as a single tube reverb with the AU side driving the reverb tranny and the AX side as the recovery side

Or as a driver output stage with the AX side as the driver and the AU side as an SE output stage

Or even in experimenting in a paraphase inverter with the AX side as the 1st inverting stage and the AU side as the 2nd inverting stage.

[boots]

Thanks Guys, sounds like they could be valuable to somebody. I will eventually put them up for sale, and will give you TAGsters first crack.

I also have a couple Mullard-made EF86's, whick I think should be worth a pretty penny. They are not a tube I will ever use (except for repairs), so I will probably put them up for sale as well. I understand they are getting very hard to find.

Also, I have a pair of 7591's (US made). They look a lot like a 6V6. I think they also were used in old Ampegs. Does anybody know if they would make a decent output tube compared to say, a 6V6?

All these tubes are pulls from an old Hammond organ, and I don't have a tube tester. However, all the AX7's I have popped into my amps sound sweet and strong. The AX7's are, of course, staying right here in Boot's own amps!

[cbass]

7591's are terrible worst sounding tube ever they are bad about exploding and causing permnet blindness I'll do you a favor and take them off your hands

[renshen1957]

Thanks Guys, sounds like they could be valuable to somebody. I will eventually put them up for sale, and will give you TAGsters first crack.

Also, I have a pair of 7591's (US made). They look a lot like a 6V6. I think they also were used in old Ampegs. Does anybody know if they would make a decent output tube compared to say, a 6V6?

Hi,

The 7591 tube is among some of the last tube designs before SS became dominant, and are very linear tubes. They are capable of 25Watts depending on the design.

Besides Ampegs, these were used in Hi-Fi Amps, Fischer, Harmon Kardon, MacIntosh, etc. The tube can command a price, the gypsy's on Fleabay certainly do charge when tested, for what it is worth. The pin arrangement is different from 6L6.

Best Regards,

Steve