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12dw7/7247 preferences

Freddie73

Freddie73

Active Member
I’m almost finished with my X-100. I am running Sovtek EL84M power tubes. A Japanese Mullard 5ar4 rectifier. GE12ax7’s rotating with Genelex 12ax7’s in the tone controls. I am not using my turntable yet. Pleased so far.
For the phase inverters it came with new production JJ 12dw7’s.
Some say the phase inverter tubes change the sound very little, I’ve found in my Fisher Receivers they make a noticeable difference.
What do you guys feel are good 12dw7/7247 tube choices for a X-100?
 
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The 7247 was one of the last RCA tubes designed specifically for audio.

Only seen 3 or 4 variants. My favorite of course is the Telefunken Smooth Plate.

Dam rare. Used Tele's and Mullards were 40 to 90$ each... Ouch.
 
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Not very many new production options available. JJ and E-H is all I've seen lately.
 
Only a few Fisher, Dynaco, Eico plus some guitar amps used them as I remember.

Half the time they were replaced with 12AX7's because many places didn't have 7247's.
 
I've used two, EH and an old set of Mullard. Frankly I can't really tell much difference in my TA-600
 
When I needed a pair for my X202B TubeDepot had vintage Mullards (branded Hammond). Their price is $50 each, you can email them and ask what brands they have in stock. Seems fair to me, given that the EH 12dw7 is $42. Also sometimes they have 10% off sales.
 
My Mullards are also Hammond branded. I forget where i got them honestly. They were used but test like new.
nate867 said:
When I needed a pair for my X202B TubeDepot had vintage Mullards (branded Hammond). Their price is $50 each, you can email them and ask what brands they have in stock. Seems fair to me, given that the EH 12dw7 is $42. Also sometimes they have 10% off sales.
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Tube Depot did not have any matched pairs today. Does anyone feel or have experience comparing JJ vs EH 12dw7.
My amplifier sounds really good but I have rolled Phase Inverter tubes in my receivers and it makes a difference. Just wanted to try different options.
 
Ok listening now to the Mullard 12dw7’s. To me, I guess the word is more forgiving, less bright, less harsh compared to the JJ’s. I can live with the JJ’s but the Mullards are , thicker, more full. The JJ’s are very detailed but can sound thin. The JJ’s on extremely well recorded music does sound better more detailed but the next song sounds thin in the middle and the upper ranges can be shrill.
I am streaming with a WiiM Pro Plus and I can improve a lot of songs to sound great with the JJ’s but the next song requires me to make equalization changes.
The Mullards are just more consistent. Easier to live with.
I can pick out 3 songs in which the JJ’s excel and if I have someone come over to hear how good my stereo can sound the JJ’s can’t be beat.
I haven’t tried the EH 12dw7 yet. Maybe next. But one can get to analytical and try too hard.
I guess I could live with either vintage Mullard or New JJ 12dw7 but the Mullards are just a little easier.
Just my opinion. YMMV.
 
Well after days of listening in my system, to my ears, the Mullards Central image is not as distinctive. No matter my positioning of the speakers. So the search continues.
 
If you feel like making adapters, the 5HA7 compactron is a very similar (maybe identical) tube. The adapter would need a resistor(s) to drop the 6.3V filament voltage. I've used them in a scratch build. There is also a 4HA7 but it needs even more filament current.
 
nerdorama said:
If you feel like making adapters, the 5HA7 compactron is a very similar (maybe identical) tube. The adapter would need a resistor(s) to drop the 6.3V filament voltage. I've used them in a scratch build. There is also a 4HA7 but it needs even more filament current.
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Would love to hear more about a ADAPTER -kinda put off on the high cost of 7247 tubes -
 
probably would involve a small PCB to go from the 12 pin Duodecar socket down to a 9 pin Noval. Male 9 pin bases aren't the most common things, so not really sure how else to get that end of it short of pins attached to a PCB.

heater is 5.6v at 0.45A, so to drop the 0.7V / 0.45A = 1.56 ohms @ 1 watt minimum resistor, but 2 watts would be better.
 
gadget73 said:
probably would involve a small PCB to go from the 12 pin Duodecar socket down to a 9 pin Noval. Male 9 pin bases aren't the most common things, so not really sure how else to get that end of it short of pins attached to a PCB.

heater is 5.6v at 0.45A, so to drop the 0.7V / 0.45A = 1.56 ohms @ 1 watt minimum resistor, but 2 watts would be better.
Click to expand...
 
If I was conversant with PCB design software this might be a good project. I measured the pins on some noval tubes and they are the same 0.040" or 1mm as the novar tubes so the 1mm brass rod should work. I used the 5HA7's in a scratch build so just used the correct socket.

@ncwalz designed a neat PCB to make 7591 to 7868 adapters. He might consider designing a 4/5HA7 to 12DW7 adapter board if it is feasible.
 
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