Anyone Know About Mullard Nos Ecc83 Cv492?

Discussion in 'The Workbench' started by cspencer, Apr 4, 2019.

  1. cspencer

    cspencer Active Member

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    I've seen a lot of Brimar CV492 but cannot find sufficient info on Mullard logo CV492. Basically, are they same as Mullard NOS CV4004?
     
  2. boola1

    boola1 Active Member

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    No, they aren't the same. The CV492 is just the military code for the standard 12ax7. There are equivalent long and short plate versions from the 50s and 60s respectively.

    CV4004 is the box plate and has lower gain than the 12ax7 , around 70 iirc.
     
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  3. cspencer

    cspencer Active Member

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    I didn't know the NOS CV4004 was low gain. I thought they were quieter because of their design but has 100% gain, same I61 and I63.

    So, Mullard does have a CV492. Were they made in Blackburn? How would you place them in terms of sound are they like I61 and I63?
     
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  4. boola1

    boola1 Active Member

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    The CV4004s are also less prone to microphonics due to their design, the reduction in noise may be because of the reduced gain.

    Yes, Mullard CV492s were made in Blackburn. I don't think you'll notice any difference in-terms of sound to their period counterparts, F92, I61 or I63s etc.

    I suspect the only difference, if there is one, is that the CV492s passed some higher testing threshold.
     
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  5. cspencer

    cspencer Active Member

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    I learnt something today. I have never heard of Mullard branded CV492's until now. Thanks for this.
     
  6. neikeel

    neikeel Well-Known Member

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    Cv4004 are great valves for extra gain stages or in the pi. The slightly lower gain is not an issue in a cascaded v1 of a 2203/4.
    The Brimars are good tubes, never seen a Mullard branded CV492 - not looked hard enough obviously!
     
    Last edited: Apr 4, 2019
  7. cspencer

    cspencer Active Member

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    If Mullard's variation of tubes was a marketing ploy in the 50s and 60s, it's still working today! I'm now tempted to buy the Mullard branded CV492 on sale.

    Edit: I just had a closer look and the tube in question was an I61. The advertisement was wrong in suggesting it was a CV492. I should have resd the fine print.
     
    Last edited: Apr 7, 2019
  8. Amadeus91

    Amadeus91 Member

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    Here is mine. It is a long plate from 1955, code is mC1 B5C. A lovely British classic.
    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]
     
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  9. MarshallDog

    MarshallDog Well-Known Member Premium Member

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    FWIW, I have tried the CP Mullard CV4004 12ax7s and
    I do not think they are low gain at all just cleaner sounding but just as loud maybe a touch brighter but rounded.
     
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  10. cspencer

    cspencer Active Member

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    Thanks for the post and pictures. This forum is starting to show up in searches. Like, what.... Marshall guys know about old tubes :wtf:

    Do you hear any difference comparing it to their long plate MC1 square getter? Or f92, f92? I found a data sheet saying the amplification is 100. Whereas, the CV4004 M8137 is 90. I wonder why they use the CV designation. I'm referring quality.

    I've got an f92, 2x CV4004 M8137 and a Brimar made Mullard CV4004. I like the f92 best for V1 and V4 (PI). I really enjoyed the M8137 in all slots. It's tone is totally different. The Brimar is also different but more airy.
     
  11. cspencer

    cspencer Active Member

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    Yeah, that's misleading. I had some CP CV4004 and the CP long plate Mullard and both we similarly loud. But they hiss quite a bit.
     
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  12. Amadeus91

    Amadeus91 Member

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    You have some fine tubes, you should try a Smooth Plate Telefunken in the PI position. Excellent.
    Another tube I really like are the Hamburg made 12AX7 Long Plates with Square getters. They sit between a Mullard and a Dutch
    12AX7 sonically. Very, very nice tubes. Look for a "D" in the tube code and that will signify Hamburg manufacture.
    I am also a fan of the Brimars. Here is a fine example of a Brimar 12AX7 that also has the CV492 designation.
    This one is from 1954.
    [​IMG] [​IMG]
     
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  13. cspencer

    cspencer Active Member

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    Hi Amadeus91,
    You're going to get me kicked out of the house :lalala: Actually, I bought a Telefunken long smooth plate and it's on its way. I am also eyeing a Brimar 12ax7 long plate. There are 4x 15mm Heerlens in my drawer hidden from sight :locked:
     
  14. Amadeus91

    Amadeus91 Member

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    Oh, Mama Mia!!!! Things just got all kinds of serious up in here.
     
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  15. neikeel

    neikeel Well-Known Member

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    CV is purely a military designation. CV4004 is the military version of the M8137. It is not specific. There are CV 4004 box anode low microphone tubes that meet the spec from other makers too.
     
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  16. MarshallDog

    MarshallDog Well-Known Member Premium Member

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    It seems to me that all Mullards are a bit noisier than other brands BUT they sound good!
     
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  17. cspencer

    cspencer Active Member

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    Hi MarshallDog,
    Are you referring to CP or old tube? The CP's seem to have a higher noise floor (hissing). I find the CP Gold Lion Gold Pins quieter. The old tubes have quiet ones (e.g. CV4004-M8137). For that, I had 3 and 1 was crackling. For I61-3, I went through some 8x and half were crackling or slightly poping. So far, all of my Philips Heerlens are quite, but they are brighter. I'm lucky enough to have a f92 working quietly in V1 of my combo. What's your experience like?
     
  18. MarshallDog

    MarshallDog Well-Known Member Premium Member

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    Well, I normally stick to CP tubes just because I dont want to get hooked on NOS tubes that are expensive and may be hard to get.

    For CP pres I really like EH, Mullards and The Tube Store 7025 Perferred Sieries depending on the amp.

    For NOS I have (1) old Mullard sounds great less hiss than Mullard CPs, some RFTs great tubes and some Jan-GE 12ax7s which sound good but I dont use these because of what I said before...yes I know stupid, guess I am collecting them!
     
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  19. Melodyman

    Melodyman Member

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    Buying 2 nos Mullard 12ax7's for say, V1, will last so long they will probably will outlive you..
     
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  20. cspencer

    cspencer Active Member

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    To be quiet honest, playing with old tubes costs a lot. In my little experience, I've already spent too much. Certainly hope the old tubes will last. So far, most of my old tubes lasts no longer than 3 months before going microphonic. It doesn't make sense. I've bought from reputable sellers as well as from the bay. No difference in terms of luck.
     
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