Yes. The RCAs are. He has some NOS tubes. You can ask him about the state of used tubes - when I buy from him they come through very strong. I use right now a set of 5751 JHSs (same as gold brand) in my McIntosh. they tested superb in my amp and sound phenomenal. Really hard to beat the prices.
Also check out ElectronTube.com, the Internet Store for DARCELL
these are 12at7 if you want them - Amperex Bugle Boy - Made in France by Mazda. You can't get better than that. they are $18 a piece!!!
Another recommendation is 7062 (same as 12at7 but taller) - they have incredible sound stage. 5 Amperex tubes for $35!!!!!!!!!!!!!!!!
I talked to them yesterday. They still have them in stock. I got both Buggle boy and 7062. ElectronTube.com, the Internet Store for DARCELL
Let me stop and summarize where I am, and what I think ive learned here.
1) Go Nos!
2) 12ax7 has the most gain, then 5751, then the 12at7
3) The 12ax7 is more similar to the 5751, than to the 12at7
4) The 12ax7 for the most part are the most expensive of the lot
The RCA black plates by description sound the most like what I want. The Mullards, perhaps second.
5) I had enough gain with the JAN Phillips 12at7 that came out of the unit, so I know another 12at7 will have enough also.
6) Will a 12ax7 have too much gain? Perhaps why the manufacturer substituted a 12at7 in its place? Unsure.
7) I am pretty sure almost any of the aforementioned will be an improvement over what I had
8) I am leaning towards the 5751 because the design adheres most to a 12ax7 with a gain similar to what I was used to in a 12at7.
1) Go Nos!
2) 12ax7 has the most gain, then 5751, then the 12at7
3) The 12ax7 is more similar to the 5751, than to the 12at7
4) The 12ax7 for the most part are the most expensive of the lot
The RCA black plates by description sound the most like what I want. The Mullards, perhaps second.
5) I had enough gain with the JAN Phillips 12at7 that came out of the unit, so I know another 12at7 will have enough also.
6) Will a 12ax7 have too much gain? Perhaps why the manufacturer substituted a 12at7 in its place? Unsure.
7) I am pretty sure almost any of the aforementioned will be an improvement over what I had
8) I am leaning towards the 5751 because the design adheres most to a 12ax7 with a gain similar to what I was used to in a 12at7.
5751 are more expensive than 12ax7 in general due to the military specs.6) possibly, but 12at7 is mu of 60, 5751 is 70 not a huge difference (don't crank up the volume)
NOS is not neccessary IHO. They cost more and there is not way to check if they are NOS. At least used are honest
Go for RCA 5751 black plates. It will be the end of your search. But for $18 experiment with 2 Amperex 7062, you might be surprised and that's not a huge investment.
6) possibly, but 12at7 is mu of 60, 5751 is 70 not a huge difference (don't crank up the volume)
NOS is not neccessary IHO. They cost more and there is not way to check if they are NOS. At least used are honest
Go for RCA 5751 black plates. It will be the end of your search. But for $18 experiment with 2 Amperex 7062, you might be surprised and that's not a huge investment.
The tube cannot be taller. (2 1/8") (standard 12ax7 height)
You may be right on the RCA 5751 black plates. I just didnt want to go used.
Last edited:
It's like buying a car. You get new you pay through the nose. You get 2 years old, you have the same awesome car, but you saved huge sum of money. I never buy a new car
It's like buying a car. You get new you pay through the nose. You get 2 years old, you have the same awesome car, but you saved huge sum of money. I never buy a new car
What is the life expectancy of this kind of tube?
Anyone's guess?
x-hours?
x years?
I probably average 75-90 hours a month of use.
that's not possible to say. Even with NOS tubes it wouldn't be possible since in a lot of cases it's been 50-60 years since the tube's produced. It usually lasts for 2-5 years depending on usage. Unfortunately, there is no test out there that would show life expectancy Mutual conductance only communicates part of the story. If you use it 8 hours a day, I would expect it to last a year or two.
Mutual conductance only communicates part of the story. If you use it 8 hours a day, I would expect it to last a year or two.that should give you about 5-6 years of life at least for a strong tube. Not a bad investment for $60-70
A JAN Philips ECG 12AT7 sounds an awful lot like a "new old stock" tube from the 1980's to me! Back in the 1990's, I collected a bunch of Philips ECG 6L6GC, 5687WB, 6922 and 12AT7WB. All have 1980's date codes. That was nearly 30 years ago, ya know. Sounds "vintage" to me...
So ART says either 12AX7 or 12AT7 will work equally well? OK. It's their circuit. I guess the tube's characteristics aren't all that important in this particular circuit. Hmmm....
--
Proposed experiment -- Let's find out how important the tube type is to the operation of this ART circuit!
First, choose a single test tone from an audio test CD, like the Stereophile CD or something like that. Measure the voltage coming from the CD player output. Or if you have an audio signal generator you can use that. Just make sure you set a frequency and level and don't change it through the course of the test.
Set a level on the ART EQ and leave it there.
- With your 12AT7's (Philips, Amperex ECC81, RCA, whatever) in there, measure the output voltage from the EQ audio outs.
- Now, leaving all settings at exactly the same place as they were, turn off the ART EQ.
- Open it up and swap in some 12AX7 or 12AX7A (or 7025, or ECC83) tubes. Put it back together, turn it back on. Let it warm up.
- Play the test track again. Measure the output from the ART EQ's audio outs.
Is there any difference at all?
--
First, choose a single test tone from an audio test CD, like the Stereophile CD or something like that. Measure the voltage coming from the CD player output. Or if you have an audio signal generator you can use that. Just make sure you set a frequency and level and don't change it through the course of the test.
Set a level on the ART EQ and leave it there.
- With your 12AT7's (Philips, Amperex ECC81, RCA, whatever) in there, measure the output voltage from the EQ audio outs.
- Now, leaving all settings at exactly the same place as they were, turn off the ART EQ.
- Open it up and swap in some 12AX7 or 12AX7A (or 7025, or ECC83) tubes. Put it back together, turn it back on. Let it warm up.
- Play the test track again. Measure the output from the ART EQ's audio outs.
Is there any difference at all?
--
Just for the record, here's how different 12AT7 (ECC81) is from 12AX7 (ECC83).
According to the RCA data sheets, with B+ of 300V, 150k load resistor, plate voltage of 100V:
12AT7 grid voltage will be -1.7V
12AT7 plate current will be 1.4mA
12AT7 gain will be 40
12AT7 internal plate resistance will be 22k
12AT7 transconductance will be 2.2mA/V
12AX7 grid voltage will be -0.9V
12AX7 plate current will be 1.3mA
12AX7 gain will be 100
12AX7 internal plate resistance will be 62k ohms
12AX7 transconductance will be 1.7mA/V
Those are very different spots in their characteristics.
The 12AX7 will be running really "hot." It would actually be running just above its maximum rated plate dissipation (1.2 watts). It would have a steep loadline, which implies higher distortion. The low bias of -0.9V might be close enough to zero volts that grid current is likely to flow (due to "contact potential").
The 12AT7 will be running at a very low current ("cold") part of its curves. The 150k plate resistor would make a pretty flat loadline, implying low distortion, but the internal plate resistance would be on the high side for this type, and the transconductance would be very much on the low side for this tube (due to the low current operation point).
The two tubes would react very differently for this one particular set of circuit parameters, even though they would both "work." They certainly would sound different. Neither would be optimal in this case, though.
--
According to the RCA data sheets, with B+ of 300V, 150k load resistor, plate voltage of 100V:
12AT7 grid voltage will be -1.7V
12AT7 plate current will be 1.4mA
12AT7 gain will be 40
12AT7 internal plate resistance will be 22k
12AT7 transconductance will be 2.2mA/V
12AX7 grid voltage will be -0.9V
12AX7 plate current will be 1.3mA
12AX7 gain will be 100
12AX7 internal plate resistance will be 62k ohms
12AX7 transconductance will be 1.7mA/V
Those are very different spots in their characteristics.
The 12AX7 will be running really "hot." It would actually be running just above its maximum rated plate dissipation (1.2 watts). It would have a steep loadline, which implies higher distortion. The low bias of -0.9V might be close enough to zero volts that grid current is likely to flow (due to "contact potential").
The 12AT7 will be running at a very low current ("cold") part of its curves. The 150k plate resistor would make a pretty flat loadline, implying low distortion, but the internal plate resistance would be on the high side for this type, and the transconductance would be very much on the low side for this tube (due to the low current operation point).
The two tubes would react very differently for this one particular set of circuit parameters, even though they would both "work." They certainly would sound different. Neither would be optimal in this case, though.
--
It would be just like a 12AX7, but with lower mu (more like 70) and slightly lower plate resistance (58k instead of 62k). Transconductance looks to be about the same at those operating points.
Still pretty far from a 12AT7. More like a very close cousin to the 12AX7.
--
Keep in mind that I'm just getting this stuff from the data sheets, not from real life.
I very much appreciate you sharing your resources btw....
Lets just assume the ART doesnt care which is in it from a stability point of view. And I dont need the extra gain that the 12ax7 delivers. Which is the better choice?
The part about the 12ax7 running "hot" looks a bit troubling. Not that I think it will start a fire, but in contrast to the relatively "cool" operation of the 12at7.
All help is welcome
The Mullard is under consideration. I did read that some find them a bit to prominent in the midrange. But like any internet blog read, you dont the the system, the device, the listeners preferences, the speakers, the room, nothing. So a comment like that may or may not be what I would hear with them.
The unfortunate thing here for me is that I need to get this right the first time. Obviously, the the folks that will try a half a dozen pairs to find the right fit have more disposable income than I. Whatever I get, its what I will be stuck with for a good long time.
If you have read this entire thread, you know that its unclear exactly what is the right tube for my ART tube EQ. So this has complicated things.
It is highly unlikely that you'll get it right the first time. It is by the nature of it that you'll burn a nice little hole in your pocket. Sad but so true !
Cheers,
Andrew.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.