RCA Greyplate vs Blackplate

Discussion in 'Amps and Cabs' started by Tommy_G, Jul 22, 2019.

  1. Tommy_G

    Tommy_G Member

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    I have 9 greys and 3 blacks in my stash.

    What do you hear as the tonal differences?

    Where in the preamp chain do you prefer to use the blacks vs. Greys ?

    What other tubes do you like to hear them with?

    (Edit: all 12ax7 long plates)
     
    Last edited: Jul 22, 2019
  2. 71strat

    71strat Member

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    Here's Timber Wolf's take on what you ask, and there's NOBODY on the forum that has any more knowledge than he does. IMHO.

    When discussing preamp tubes, I'd assume you mean 12AX7. Mid-'50s black-plate RCA 12AX7 break up sooner than later-production gray-plate types, and there are several variants of those gray-plate types. The black-plate 12AX7 can't be beat for their clarity, in my experience, but don't support your goal of glassy 3D cleans as well as gray-plate 12AX7. Of those gray-plate types, the long gray-plate doesn't hold together as much (i.e. breaks up a little sooner) as the short-plate types, even though they generally have greater clarity than the shorts. The short-plate 12AX7A has less harmonic complexity, which, at greater clean volume can really support the glassy quality. The short-plate 7025 has more harmonic content, and generally more lean (less bass flub) & bright (upper mids) tonal character than the 12AX7A. I suspect you'd most appreciate this short-plate 7025. Generally speaking, the short-plate 12AX7 types will tend to be less microphonic than the long-plate types, so that would also be a bonus for early gain stage use (i.e. the first input tube position, "V1").

    So - short summary: RCA 6V6GTA and short-plate 7025. That is, if you're limiting your choices strictly to RCA.

    BTW - if you want to go to 6L6GC, then I'd recommend GE over RCA black-plate 6L6GC for 3D glassy cleans.
     
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  3. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Thanks for your kind words, @71strat

    RCA made at least two distinct variants of long black-plate 12AX7. The most commonly available now are those made from the mid-late '50s. I find those earliest 12AX7 to be intriguing, however. Here are excerpts from my tube notes:

    RCA ‘40s long black-plate 12AX7 wide D-getter – Lows more lean than its younger ‘50s counterpart, and breaks up a little less easily. Superb articulation; bright clarity. Note that black plates are a bit more glossy (eggshell finish). [here's a post with a photo]

    RCA mid-late '50s long black-plate 12AX7 square-getter – Great articulation and early breakup, like the Raytheon 12AX7A, but fatter and meatier lows, bright, open highs, less “colorful” overtones and “dry” feel to it. Really rips when driven! Plates are flat black. Note: late-‘50s/early-‘60s black-plate 7025 are similar, but perhaps a little less raw, or more refined.

    RCA ‘50s long gray-plate 12AX7 square-getter – Solid lows (not as fat as later short-plate RCA 12AX7A), mids well-defined, but not as open, bright and lively as older RCA black-plate 12AX7s. Like a cross between RCA long black-plate/square-getter and short gray-plate RCA 7025: breaks up a little earlier than the short-plate 7025, giving it a liveliness; less harmonic content than the mid-late '50s long black-plate and breaks up later, but is somewhat less articulate. This gray-plate RCA 12AX7 and later short-plate versions are a bit more compressed than the older black-plate versions. Has wonderful “chime” in V1 of AB763 circuit. Note: similar long gray-plate style ’59 7025 sounds the same to me.
     
    Last edited: Jul 22, 2019
  4. 71strat

    71strat Member

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    Facts are facts though. You've probably forgotten more than most will ever know about tubes. I know very little technically, and opinion on only the ones Ive used. But I know what I like with the types of amps I use.

    You also know a lot about the physical construction of the tubes, which to me is very impressive, especially considering for how long these types of tubes have been out of production. Which is multiple decades.
     
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  5. Tommy_G

    Tommy_G Member

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    The numerals on one of the greyplate tube is 60-09 and a 274 (the 6 is a little messed up so its a best guess).

    A square getter in too on one side of the glass.

    Presume it corresponds with the last entry in Timbre Wolf's remarks.
     
  6. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    274 is the EIA code for RCA. And the "60" would match the year of manufacturing for the long gray-plate 12AX7. Sounds exactly like the last version I discussed.

    One thing to consider is that, even if you purchase from a well-meaning seller who has diligently tested the tube on their maintained tube tester, there are two common sonic concerns that won't show up unless the tube has been tested in an appropriate audio circuit: microphony and noise. The mid-'50s black-plate 12AX7 seem to be more frequently plagued by these terminal flaws. So buyers beware!

    I use different tubes for each amp. And I've ended up not liking either of these as much as other 12AX7 types I prefer - even though both are very good. One thing I find kind of grating is that the black-plate RCA 12AX7 breaks up in a way I don't like - for some reason the breakup sounds/feels kind of like tearing thick construction paper, to me. Some may favor it, however, and those mid-late '50s RCA 12AX7 might be just the thing for a tweed amp.

    What amp are you considering these for? Whatever it is, if there is too much microphony, you might have to move the offending tube from V1 down the signal chain, where it might end up as a phase-inverter by default, due to microphony. Or maybe you'll get lucky, and can keep it in V1.
     
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  7. Luca1979

    Luca1979 Supporting Member

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    Is there another 12AX7 with the same glorious RCA cleans, but without the "tearing thick construction paper" effect when overdriven? I get what you mean, it's an appropriate sonic description!
     
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  8. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    I guess it depends on what you mean by the same glorious RCA cleans... There are several amazing 12AX7/ECC83 types with amazing clean sounds. There are earlier-breakup cleans, late-breakup cleans, cleans with lower-mid emphasis, cleans with upper-mid emphasis, cleans with bright treble, cleans with harmonic overtones, cleans with more fundamental tones. I'd say the one thing that unifies my favorite clear/articulate clean sound tubes is that they seem to mostly have long-plates.

    The question I have is - what do you identify as the RCA glory? Is is a tonal signature? Breakup dynamics? Compression? Perceived harmonic content? Range of tonal representation?
     
  9. silver surfer

    silver surfer Member

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    I have about 35 RCA and GE pre amp tubes - short plates, long plates, grey and black. I consider my ear pretty good and can hear differences between those tubes and current production tubes as well as with Mullards and some others I have, but I'll tell you, I hear little if any difference between any of those RCA's or GE's in my BF Fenders. They just all sound good. I play soft and very loud, clean and well pushed. So kudos to Timbre Wolf and others for having such a discerning ear, but to me those RCA's and GE's are all gems.
     
  10. Tommy_G

    Tommy_G Member

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    @Timbre Wolf

    Tested all available for sale for microphonics (but not for noise) in an amp and rejected three of them being offered due to microphoncs. All at conversation volume. Never boosted volume enough to really check for noise but I did hear some.... I would say in general the tubes seemed just a bit weaker than my blackplate I tested against.

    I got 6 RCA longgreys, 1 RCA longblack, 1 GE black and paid $7.50 each. They seemed adequately strong for a guitar amp application.

    My sense was that the RCA BP was definately a sweeter, more treble, but perhaps thinner sounding tube for cleans than the RCA greys.. but believed the greys had a smoother top and fatter lower mids that might work better in a band mix. I preferred the more "open" clean amp feel of the blackplates.

    This rough opinion seems to jive somewhat with some of the above comments.

    I bought them to replace my stash of microphonic New Production tubes.

    I tend to agree there are "better" tubes. But for $7.50 apiece.. I can live with these.
     
    Last edited: Jul 23, 2019
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  11. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    ooh! Good deal!

    Is that a GE black-plate 12AX7? If so, then that's a very exciting tube to me - exceptionally clear, bright, raw.
     
  12. Tommy_G

    Tommy_G Member

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    The GE has the code 5-35, is a shiny gun metal dj grey/ black (not unlike a Raytheon coating ) iirc, side getter. Cant see getter shape as its hidden behind the flash on the sidewall.

    I have another GE tube.. bought it off a tube dealer as a 12AT7 but am somewhat convinced is a 12AX7.. very bright and breaks up perfectly as a PI. Very much my favorite PI in dark bloated amps.
     
    Last edited: Jul 23, 2019
  13. Krausewitz

    Krausewitz Member

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    $7.50 apiece!? What a great deal!

    Where from?
     
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  14. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Side-getter? Does it say “Canada” on it? Got a photo?
     
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  15. dsmc80

    dsmc80 Member

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    MMMM. I love those tubes. Still have about 30 NIB that were spares from an old organ.
     
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  16. Tommy_G

    Tommy_G Member

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    Yes. Under 12AX7 it says Canada
     
  17. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Those "clear top" 12AX7 from Canada are different from US-made GE 12AX7. I believe they were made by Canadian Marconi (a.k.a. Canadian GE and/or Radiotron), which had past ties to both GE and RCA. They break up later than '50s RCA long black-plate 12AX7 (and also early-'50s GE/Ken-Rad black-plate 12AX7), and have superb clarity and a lean bright tonal character. I'm grateful to @dsmc80 for introducing them to me many years back.
    [​IMG]
     
  18. dsmc80

    dsmc80 Member

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    I'm quite thankful for your tube knowledge in general Thom. You are a wonderful resource on this forum. :aok
     
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  19. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Thanks very much!
     
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  20. Tommy_G

    Tommy_G Member

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    Cool. My first taste of Marconi. Sounds Italian.

    What kind of circuits do they sound best in?
     
    Last edited: Jul 23, 2019

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