RCA 12BH7 Black Plates versus Grey Plates

[Ron Resnick]

With regard to RCA 12BH7s what are the sonic advantages and disadvantages of the grey plates and the black plates? How do the grey plates and the black plates sound different?

Which do you prefer, and why?

 

[mulveling]

My favorite of the RCA 12BH7 were the very earliest version with "winged" black plates. Late 1940s - early 50s. By "winged" plates it means each plate is asymmetric, with stapling/crimping on only one side. All later RCA 12BH7 had staples on both sides of each plate. These tubes were the lushest, most full-bodied, and organic of all - not just of RCA's variants, but of all 12BH7 makes I've tried. Unfortunately, they tend to be fairly noisy and microphonic. Good for driver slots in amps. Not good for preamps - though that's a common "feature" with all 12BH7.

As far as RCA black plates with the normal "ladder" plates (1950s) - they seem decent, but I also had bad luck picking up many worn-out tired tubes of this type. I might not have heard the best representation of this type, but still feel they ultimately lack winged-plates' magic. You get more of that 3D, "holographic" goodness with the winged plates.

The RCA gray ladder plate 12BH7 are solid tubes. Nice mildly warm sound - not as lush or magical as the winged black plates, but they do a good job and should be much easier to find in good condition.

My favorite 12BH7 of all is the Sylvania shiny black oval/curved plates, with D or square getters. I stopped using RCAs when I got these, but unfortunately they're much harder to find (especially if you need matched pairs or quads). Don't bother with later Sylvania gray plates of this type - they sound HORRIBLE by comparison (bright, with sterile midrange). Some sellers will advertise dark gray plates as "black plates" so you have to be careful. The Sylvania black plates have better detail, clarity, and dynamics that any RCA, but still have just enough sweetness in midrange to keep on the musical side of things. More neutral than RCAs. Tung-Sols look very similar to this build (probably got their plates from Sylvania) but with heat-sinks on the posts and slightly different mica spacers - these tubes have a brighter, leaner balance than neutral. Still good, but not AS good as the real Sylvanias.

Also have some Japanese curved-plate 12BH7 that are interesting just because they have gobs at dynamics and slam, but unfortunately at the expense of midrange sweetness and musicality / liquidity. Really "different" sounding tube!

Haven't tried any "pinched" plate variants, nor the Electro Harmonix modern version. As usual, massive re-branding and shared parts between manufacturers makes it harder to parse out what a tube actually is. I've had some Westinghouse tubes that look like the RCA winged-plates but don't sound as good.

 

[miniguy]

My favorite of the RCA 12BH7 were the very earliest version with "winged" black plates. Late 1940s - early 50s. By "winged" plates it means each plate is asymmetric, with stapling/crimping on only one side. All later RCA 12BH7 had staples on both sides of each plate. These tubes were the lushest, most full-bodied, and organic of all - not just of RCA's variants, but of all 12BH7 makes I've tried. Unfortunately, they tend to be fairly noisy and microphonic. Good for driver slots in amps. Not good for preamps - though that's a common "feature" with all 12BH7.

As far as RCA black plates with the normal "ladder" plates (1950s) - they seem decent, but I also had bad luck picking up many worn-out tired tubes of this type. I might not have heard the best representation of this type, but still feel they ultimately lack winged-plates' magic. You get more of that 3D, "holographic" goodness with the winged plates.

The RCA gray ladder plate 12BH7 are solid tubes. Nice mildly warm sound - not as lush or magical as the winged black plates, but they do a good job and should be much easier to find in good condition.

My favorite 12BH7 of all is the Sylvania shiny black oval/curved plates, with D or square getters. I stopped using RCAs when I got these, but unfortunately they're much harder to find (especially if you need matched pairs or quads). Don't bother with later Sylvania gray plates of this type - they sound HORRIBLE by comparison (bright, with sterile midrange). Some sellers will advertise dark gray plates as "black plates" so you have to be careful. The Sylvania black plates have better detail, clarity, and dynamics that any RCA, but still have just enough sweetness in midrange to keep on the musical side of things. More neutral than RCAs. Tung-Sols look very similar to this build (probably got their plates from Sylvania) but with heat-sinks on the posts and slightly different mica spacers - these tubes have a brighter, leaner balance than neutral. Still good, but not AS good as the real Sylvanias.

Also have some Japanese curved-plate 12BH7 that are interesting just because they have gobs at dynamics and slam, but unfortunately at the expense of midrange sweetness and musicality / liquidity. Really "different" sounding tube!

Haven't tried any "pinched" plate variants, nor the Electro Harmonix modern version. As usual, massive re-branding and shared parts between manufacturers makes it harder to parse out what a tube actually is. I've had some Westinghouse tubes that look like the RCA winged-plates but don't sound as good.

I have Sylvania gray plates driving the KT88s in my amp which has never sounded better. Again, horses for courses.

 

[Powerman]

Now the question is where to find them? Seems with my other signal tubes it was a bit more clear cut... Black plates or clear tops, bugleboy, long plates. The 12BH7s seem much more mashed up. This shade of Grey plate, pinched ladder many different getters. Hard to trust what some say as good and what others say they have. I'm trying to find some Sylvanias... There are plenty, just don't know what exactly they are. I have some RCAs coming but I'm not entirely sure what they will be.

 

[Ron Resnick]

Thank you very much, mulveling, for that very detailed reply! I appreciate it!

 

[Argonaut]

Ron , I would also recommend 50’s TungSol shiny black oval plates sporting horseshoe getter (Early 50’s) or slightly later halo getter ( mid to late 50’s ) , I use a pair on inversion phase duties in a Sansui AU-111 integrated amplifier circa 1965 , they major on tone and texture in a very similar presentation to the black plate RCA’s but with perhaps a touch more openness in the upper octaves imho ymmv

Viz :

https://www.ebay.ca/itm/225477609924?hash=item347f8349c4:g:QRcAAOSwToBjrjoe&amdata=enc:AQAIAAAAwMxG4egqCeCg6SzJBeFiFNRVLRKLrYr7GiWnE0l0EP5feDkJhCny7jpNgVSbp2zi7ShQTsosvzYnKmpIo/B4JVUoFRv5HYjnqw81oqENr73Cmq6kJmYPtiUgHEuJBH6pyWnTnzzBw+QZhWfWsE33WyrN7cJLt7Qx2jisdE4GU+coKVGik/DeCRF2d3ODnUVHkL/ehF4f4ztD+A+J9H3usvygSfNpI3D1aOJOxdp6ez4S6dULTM+SCkcvgxFizBgPPA==|tkp:Bk9SR-6V7vjvYQ

 

[Powerman]

Well I have a pair of Sylvania black oval plates supposedly 55. I can compare this to the RCAs whenever those decide to show up.

 

[Powerman]

A little disappointing. Sylvania and RCAs seem to rule, some little difference. I got my Sylvanias which are the black shiny oval plate.... I don't know how good they actually are, I just know they are a clear step back from the Mazda 12AU7 in their place. I mean not even close. When I tried all my other 12AU7s what Lami says is true... Little differences but not large changes like amp. So I expected not big changes, but better just because bigger tube... It killed stage, weight, resolution. I'm still waiting for RCAs, but I'm questioning that already.

 

[Powerman]

So just an update to this... I don't ever assume NOS tubes have no time on them. I did put a day on the Sylvania, but again a clear step back. I recently got other tubes and they had zero hours on them. The heaters developed spots above them from burn in. Well, those definitely got better. So I tried the Sylvania again. Not bad. I put more time on them. Ya, I think they were brand new. It's true what Lampi says, that position doesn't have big impact on sound, but they definitely equal the Mazdas. If I had to say, I would give them the edge. They sound a hair bigger... Stage, space, air. Top to bottom is good. So I'm running them. The Mazdas go back to spares for my amp. In this case, I didn't put enough time on them and they are definitely keepers.