CV492 same as a 12AX7?
- The Break Room
- Fender Amps
- Tech Bench
- Tubes
- Speakers
- The Instrument Room
- Mesa Amps
- Marshall Amps
- Small Amps
- Boutique Amps
- For Sale
- Other Major Amp Brands
- Introduce Yourself
- Solid State Amps
- Effects
- Other British Amps
- Sound Reinforcement
- Recording
- Important Announcements
- Hammond Organs & Leslie Cabinets
- Shameless Promotion
- The Boiler Room
CV492 same as 12AX7?
| Author | Comment | ||
|---|---|---|---|
 Idunknow |
CV492 same as 12AX7? |
Lead | |
|
Posts: 22 (03/04/09 19:18) |
|
||
|
SG123 |
|||
|
Posts: 8146 (03/04/09 19:26) |
According to this, probably close enough:
http://tdsl.duncanamps.com/show.php?des=CV492 CV in case you didn't know, is a British designation meaning Civilian Valve - as opposed to military valve, I suppose. It's interesting that the Duncan listing for 12AX7 doesn't list the CV492  [ the 12AX7-A listing does, however ]
CV4004 is one I see a lot and know for sure is a direct replacement.
So many
frequencies, so little time...
|
||
|
Idunknow |
|||
|
Posts: 23 (03/04/09 20:17) |
I understand it is basically the same as a M8137 or CV4004. From what I read all 3 tubes are basically the same tube. But I am not sure what I read is true.
That's what I was tring to find out. One site the Virtual tube museum says that the CV4004 is based on the CV492 & several other tube sites say they
are the same tube.
Last Edited By: Idunknow
03/04/09 20:35.
Edited 1 times.
|
||
|
Idunknow |
|||
|
Posts: 24 (03/04/09 21:02) |
Check this site out. The Seimens CV492 is Dr. Z favorite preamp tube it says. The are actually Prewar EI tubes, I guess.
http://www.tejastubes.com/SiemensCV492.htm http://www.tejastubes.com/12AX7.htm |
||
|
SG123 |
|||
|
Posts: 8148 (03/04/09 21:11) |
How do we make the leap from Dr. Z liking EI 12AX7 to the Siemens CV492 - except that his quote is on the same page ?
Same factory ? EI was a great sounding tube [ from what I've read ], but very prone to becoming microphonic.
So many
frequencies, so little time...
|
||
|
Idunknow |
|||
|
Posts: 25 (03/04/09 21:45) |
I don't know either. That's why I said I guess! It want you to presume that is a pre war EI tube.
did find this. & now after all that i just don't care anymore! goodby! http://tdsl.duncanamps.com/show.php?des=12AX7
Last Edited By: Idunknow
03/04/09 22:02.
Edited 3 times.
|
||
|
EMan |
|||
|
Posts: 5315 (03/05/09 09:51) Hell Yes, I'm from Texas |
Simply, the only way to determine if a tube is compatable with another tube - is to pull the data sheets on them, and compare their charactersitics.
Make some copies of the Plate Characteristic Curves, and plot load lines from parameters common in the circuit you intend to install the tube into. This will give you an idea of how different tubes will react in similar circuits.
"I haven't failed, I've just found 10,000 ways that don't work."
- Thomas Edison - |
||
|
Idunknow |
|||
|
Posts: 27 (03/07/09 18:26) |
Well, my curiosity was to much for me to not buy a Mullard CV492 just to see what some of the hype was about, so I did and was very glad I did. It sounds so
close to the 12ax7 mullards I use in my amp now that it is hard to describe any difference at all except that it sounds a little more, not much but a little
more articulate & defined in its tone, but that could be just the difference in any 2 different tubes even though they are the same tube, from my
experience. Same short ribbed grey plate & halo. Good gain just like a normal mullard. Will have to listen to it and compare for a while before I make
final judgement. It does sound more clearer & defined in its tone it seems & right now if I was to do a blind test with one of my other 12ax7 mullards
I would be hard pressed to be able to tell the difference.
|
||
|
EMan |
|||
|
Posts: 5319 (03/07/09 19:57) Hell Yes, I'm from Texas |
"...Good gain just like a normal mullard..."
This is the kind of statement that confuses me. What exactly is Mullard "good gain"? Is there some number associated with that, as compared to some other same type tube?
"I haven't failed, I've just found 10,000 ways that don't work."
- Thomas Edison - |
||
|
Idunknow |
|||
|
Posts: 28 (03/07/09 20:48) |
Just a figure of speech but you wouldn't understand unless someone did give you exaact figures. Sorry that your so sensitive to such figures of speech
& everything has to be so technical. It is better to serve & help than to always be a critic. Some use their intelligence to show people how smart they
are and to critique everything and find fault where ever they can to prove what ever they need to prove & some use there knowldge for no other reason than
to help others for no reward and these are rare people in these day and times. Egotisim is always a ugly virus that infects the human race & intelligence
has nothing to do with wisdom. I don't believe I desire to come to this forum any more or do I belong on it. So, I leave you to your dismal life!
|
||
|
StoSoStu |
|||
|
Posts: 425 (03/07/09 21:06) South of the Border..way South! |
What a prat...............
Bob
The road goes on forever and the party never ends |
||
|
SG123 |
|||
|
Posts: 8156 (03/07/09 22:00) |
Fact:
Take ten or more tubes of any brand and same construction - new stock or old - and there will be a significant difference in their measured characteristics. Here is a posting from Myles Rose who actually measures tubes and knows how one parameter affects another. It's data from JJ803S [ 12AX7 equivalent ] - data from a sampling of remaining old stock Mullards will also have variation. JJ803S test results October production run Below is the latest run from 10/17 of the JJ 803S tube. This is a direct 12AX7 replacement. This last run was in line with the previous run with perhaps a little more spread (read a little less consistency) in some areas. The average plate current output was 1.0mA (expected design spec is 1.2mA) The average transconductance was 1496 (expected design spec is 1600) The average actual gain in circuit is 93.5 (expected design spec is 100). This is higher than any current production tube at the moment. Most tubes today are in the 80-85 range. The test voltages were book spec: 250 plate volts, 2 volt bias. Expected plate resistance was 62.5k and these tubes had an average plate resistance of 62.6K which is as good as it gets. This is a big part of the reason that these tubes have proper gain. Most production tubes today have low plate resistance and this results in lower gain. The spread on gain ranged from 86.9 to 99.5 which is a 12.6% spread. This is very good for today's production tubes. The transconductance ranged from 1010 to 1920 which is a 56.9% spread. This is not very good but is typical of today's production tubes. Low TC coupled with low plate resistance will produce low gain and this is why most other production tubes today have lower average gain. Plate current output ranged from 0.6mA to 1.6mA which is a 83.3% spread. The average was 1.0mA which is acceptable and should work well for driver applications such as reverb drivers, effects loop use and phase inverters. I hope JJ addresses the spread of this plate current to tighten things up a bit in the future. Overall, this is a great run of tubes and may be some of the best work at the moment in the 12AX7 business. In the end your own ears are the final judge as these tubes do have their own unique tone and response. Below are some of the individual results. Two lines equal the results of one tube as there are two triodes in each tube. The first number is the plate current output. The second number is the transcondductance. The third number can be ignored as it is one of the pieces of data used for plate resistance. Plate resistance is not to be thought of in the same way as resistance of a resistor. It is a label that involves many factors and is more like impedance of say a speaker than resistance. Plate resistance will change depending on the voltages applied to a tube so it is not a fixed number. The last number is the true gain of the tube in circuit at 250 plate volts and 2 vold bias. Some people use the term mu and this is NOT the same as gain. Mu or mutual conductance or transconductance is a form of voltage gain but there are other factors when it comes to actual gain in a circuit. You can have very low mu/TC but if the plate resistance is high you can have high gain as an example. It is always best if a given tube comes close to design spec in all parameters. 1.1 1630 0.018 90.6 1.3 1920 0.0205 93.7 1.3 1820 0.02 91.0 1.1 1650 0.0175 94.3 1.4 1850 0.02 92.5 1.4 1870 0.0195 95.9 0.9 1420 0.015 94.7 0.7 1310 0.014 93.6 0.9 1440 0.016 90.0 1.1 1700 0.018 94.4 1.0 1370 0.015 91.3 1.3 1840 0.019 96.8 0.6 1120 0.012 93.3 1.1 1640 0.017 96.5 1.0 1500 0.016 93.8 1.2 1730 0.018 96.1 0.7 1130 0.013 86.9 0.8 1310 0.014 93.6 1.6 1890 0.019 99.5 1.3 1650 0.018 91.7 0.8 1270 0.014 90.7 0.6 1010 0.0115 87.8 1.1 1520 0.016 95.0 0.9 1370 0.0145 94.5 1.5 1750 0.0185 94.6 1.0 1430 0.015 95.3 1.6 1860 0.02 93.0 1.2 1730 0.0175 98.9 1.0 1400 0.015 93.3 1.2 1660 0.017 97.6 0.7 1130 0.012 94.2 0.8 1320 0.014 94.3 1.0 1360 0.015 90.7 0.7 1140 0.0125 91.2 1.3 1760 0.0185 95.1 0.9 1410 0.015 94.0 0.9 1480 0.015 98.7 0.6 1090 0.012 90.8 0.6 1070 0.012 89.2 0.8 1300 0.014 92.9 -end- -------------------------------------------------------------------------- I agree that "good gain like a normal Mullard" is a vague statement at best. Actually, I'd be more inclined to believe "good tone like a normal Mullard".
So many
frequencies, so little time...
|
||
|
StoSoStu |
|||
|
Posts: 428 (03/08/09 03:34) South of the Border..way South! |
I don't see how gain can be good. You can have more or less gain, but good gain?
Bob
The road goes on forever and the party never ends |
||
|
SG123 |
|||
|
Posts: 8161 (03/08/09 06:56) |
But NO gain would be bad.
So many
frequencies, so little time...
|
||
|
EMan |
|||
|
Posts: 5320 (03/08/09 09:05) Hell Yes, I'm from Texas |
Nice data collection, SG. I've got a link somewhere's that runs the test(s) with respect to perveance.
"...Sorry that your so sensitive to such figures of speech & everything has to be so technical...." Most of the folks here *are* technically oriented, and those that are not so, are making an honest attempt to get better at it. Questions like the one I posed are not an attempt at redicule, but a way to solicit useful information for the group ( regerence SG's data series above ). It's also perfectly acceptable here to say "I don't know".
"I haven't failed, I've just found 10,000 ways that don't work."
- Thomas Edison - |
||
|
Andy ZZ |
|||
|
Posts: 2488 (03/08/09 09:41) |
"So, I leave you to your dismal life!"
An astute description of how the Amp Workshop has been percieved by you, as demonstrated by your postings. However, to us, it only feels that way when you are here. So please, dont let the door hit you.... -andy-
It aint the years, it's the mileage...
|
||
|
jbmojo |
|||
|
Posts: 288 (03/08/09 11:10) |
Sounds to me like he belongs on one of those other forums with the other rude people.
Or, he hasn't had his daily slappin'. 
Ninty-nine percent of failures come from people who have the habit of making excuses.
|
||
|
RussBert |
|||
|
Posts: 721 (03/11/09 14:17) |
FACTS, we don't need no stinkin' FACTS!
I just want to say how good my expensive tubes sound |
||
|
SG123 |
|||
|
Posts: 8172 (03/11/09 17:40) |
But do they have good gain ?
So many
frequencies, so little time...
|
||
|
EMan |
|||
|
Posts: 5338 (03/12/09 12:54) Hell Yes, I'm from Texas |
Like Billy Joel sang - 'ya get more milage from a cheap set of valves'.
Or was that speakers?
"I haven't failed, I've just found 10,000 ways that don't work."
- Thomas Edison - |
||
|
StoSoStu |
|||
|
Posts: 440 (03/12/09 18:55) South of the Border..way South! |
I thought it was white wall tyres..............
Bob
The road goes on forever and the party never ends |
||
- The Break Room
- Fender Amps
- Tech Bench
- Tubes
- Speakers
- The Instrument Room
- Mesa Amps
- Marshall Amps
- Small Amps
- Boutique Amps
- For Sale
- Other Major Amp Brands
- Introduce Yourself
- Solid State Amps
- Effects
- Other British Amps
- Sound Reinforcement
- Recording
- Important Announcements
- Hammond Organs & Leslie Cabinets
- Shameless Promotion
- The Boiler Room
