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I have a few Mullard CV4004 from one dealer and I ordered another one from another dealer but the label is different and doesn't say CV4004. Both are reputable dealers. Should I look into this further? I want them to match sonically.
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What did the second set have written on them? There are other decscritors for the CV4004, is a 12AX7 or very close to it not exact.
Steve
The label says 12AX7 CV49 RB/D. There's more but it's worn off. I just compared the plates on it to the plates on the CV4004-labeled tubes I have and they're quite different.The thing is, I use these tubes in pairs and this one is a backup so at some point this tube will be on one channel with one of the other tubes on the other channel.
Edits: 10/18/15
CV492 . It is the government designator for 12AX7 / ECC83 and will have a 14mm or 17mm 'ladder plate' . CV4004 is a ruggedised type , a Mullard will have the distinctive 10mm square 'box plates'
Al
So if it's labeled CV492 it isn't a CV4004? Do they sound the same (doubt it)?
All CV-4004s are "select" premium tubes, with low noise and long life properties. CV 4004 types have various plate structures and "halo getter" sizes. Unfortunately, through the years, many 12AX7 tubes have gotten "rebranded." Each type has some unique sonic properties, if your system has good resolution capabilities.
Without seeing exactly which type you have, typical CV-4004s are known as the "half box plate with single flange" as found on the original Brimar 6057 Trustworthy T series. These sound excellent, especially with the large halo.
Some CV 4004s have the chunky box plate, as found on the original Mullard M8137; considered by some a supreme tube. These also sound wonderful, but a bit forward compared to the nice depth possible with the half box plates.
The CV-492 is usually a "small plate" 14mm tall. These are "select" high quality tubes that sound very similar to the similar looking, typical Mullard or Amperex small plate varieties. Fortunately, this is a very popular, classic sound.
If you were to set up one channel with the chunky box plate and another channel with a smaller plate type, the soundstage and harmonic structure might get confusing. Then again, you might even enjoy the variety...it is your playback enjoyment at stake and only you can decide which types and setups you prefer...Enjoy the tube rolling journey...
'All CV-4004s are "select" premium tubes, with low noise and long life properties. CV 4004 types have various plate structures and "halo getter" sizes'
Huh ? Where did you see this ? Mullard CV4004 is not specifically a 'select' or 'low noise' type . The data does state that it is a reliable type though . It has unique construction compared to other ECC83 and is a ruggedised version (as are all CV4xxx devices) . Plate style stayed the same throughout production with the best sounding examples being made in the early 1960's
Never mind the hearsay , here's the spec sheet...
Al
Hi Al, thank you for the important information. the spec sheet does show both a noise test and vibrational noise test towards the end of the specifications requirement contract. So, supposedly the CV4004 need to pass a test of less than 100mv, if I am correctly reading the chart. However, I did not compare the passing value of that test compared to what is considered a "low microphonic" tube. cheers, Dak
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