A Cool Tube, the 12DW7/7247/ECC832

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A Cool Tube, the 12DW7/7247/ECC832

Postby ricochet » Wed Jun 07, 2006 12:14 am

I just posted this over on http://music-electronics-forum.com/ and thought it might be of interest over here:

This is a very useful tube for a lot of amp applications, with one half of a 12AX7 and one half of a 12AU7 in the same envelope. JJ is currently making a version as the ECC832, and also offers a version with the sections reversed. It has no officially recognized international designation, but JJ calls it an "ECC823." I think it might be VERY interesting to harpers who want a lower gain tube in the first stage of an amp but don't need to drop two stages to such low gain as a 12AU7's. I'm sure you can think of many other situations where this combo would be very useful, such as a reverb drive and recovery tube.

Here is the JJ spec sheet for their version(s) of this tube: http://www.jj-electronic.sk/pdf/ECC%20832.pdf

8)
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Postby jeffl » Wed Jun 07, 2006 12:32 am

Muchas gracias para la informacion. I knew it wuz yer post when I saw the title.
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Postby guitarslim101 » Wed Jun 07, 2006 1:18 am

Sounds like an interesting one.
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Postby t bone bruce » Fri Jun 09, 2006 4:49 pm

Sounds cool, I'll look into getting one and trying it out. Incidently any UK harpers wanting odd tubes like this can try http://www.chelmervalve.com
These guys are local to me, and I ring them up and collect in person. They have just about anything in stock, and they're very reasonably priced.
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Postby thebluesbox » Sat Jun 10, 2006 7:07 pm

I think this is a very cool concept your right most times if a 12ax7 is too much and you put a 12au7 it drops too much gain, now I dont really know about the 12ay7 and the 12at7 I thought those were the in between tubes and can serve the same purpose at between au7 as ax7's?
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Postby ricochet » Sat Jun 10, 2006 8:00 pm

Yes, they're in between, with symmetrical halves. This is yet another option. It'll give different results.
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Postby t bone bruce » Fri Jun 23, 2006 5:59 pm

Well I got out of work early today and picked up the last 12DW7 in stock at my valve suppliers. It now resides as the pre-amp tube in my champ/princeton clone. I like the result- crunchier than the 12AU7 by a long way, maybe even more than with the 12AT7 I'd used, and less feedback prone than the 12AT7. Now all I've got to do is try it at a gig....
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Postby ricochet » Fri Jun 23, 2006 6:14 pm

Cool!
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Postby t bone bruce » Sat Jul 01, 2006 8:36 am

I took the amp out to a jam on Thursday. It worked really well with the 12DW7 as the preamp. I got a nice dirty sound with a great warm breakup. The amp seems louder too. I had to use the Micro-Hush to avoid feedback, as the venue is small and I was positioned quite close to the speaker path of the amp.
This tube seems to have made a real difference in the amp's tone and sound. If you're using a small SE amp with one pre-amp tube like the champ, princeton, valve junior or similar, and using a 12AU7 or 12AY7 then give one of these a try!
Thanks for switching me on to this tube Rico!
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Postby ricochet » Sat Jul 01, 2006 3:18 pm

Glad you like it, Bruce. :D
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Postby dblues » Fri Aug 04, 2006 3:35 pm

After much research on this, I was informed to put this tube in the phase inverter slot (preamp tube closest to the power tubes) Not good for guitar but supposed to work great for harp. Don't have the tube yet for a couple of days, but when I get it I will let you know what happens.
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Postby ricochet » Fri Aug 04, 2006 3:45 pm

It'll be interesting to try it in the phase inverter. What it'll do is to GREATLY imbalance the two output tubes. One will be driven much harder (and run hotter) than the other. The sonic effect will be that it'll reduce the total output power substantially (because of the one output tube being underdriven by the 12AU7 half), but you won't hear that. What you'll hear is a lot of second harmonic distortion, which most folks like in an instrument amp. Even harmonics can't be produced in a perfectly balanced push-pull stage; they're totally cancelled. Some imbalance is deliberately built into lots of phase inverters for that reason, and I'd never go to the trouble of getting one of those "matched twin triodes" for a PI. Whether you'll like it as unbalanced as it'll be with the two tube sections at amplification factors of 100 and 18 remains to be seen. Won't hurt to try it, though. If I were running an amp that way, I'd "rotate" the output tubes frequently so they'll wear evenly.
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Postby dblues » Sat Aug 05, 2006 11:27 pm

I received the tube today and here is what happened.
By the way. this is a Fender Blues Deluxe original (1994) I did this in.

I exchanged the ECC832 with the 12AX7 that is in V3 (phase inverter)
I already have a 12AU7 in place of a 12AX7 in V1. This by the way makes the most difference in being able to turn up vol before feedback. Not sure if it's any louder per se but more controllable
V2 is a12AX7
The only difference I could detect using the ECC832 was a very slight earlier breakup and the ability to further turn the vol (slightly) without feedback.
I did this on the normal channel and the drive and master volume settings. The normal channel works better IMO. I used a JT30 with a Shure CM element (USA) It sounded better than my JT30 with the original MC151 element.

Bottom line, using this on stage at a live gig, don't think I or anyone else would have heard any differences at all.
If it were a loud gig I would still either mic the amp or use the line out to the PA
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Postby ricochet » Sat Aug 05, 2006 11:34 pm

If you put an oscilloscope on the output you'll see the second harmonic from the grossly imbalanced PI, but since that's an octave of the fundamental it's really fairly subtle sounding.

I snicker at golden eared audiophiles.
:lol:
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