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.

 

[Atriya]

Not good for preamps - though that's a common "feature" with all 12BH7.

Did you mean to say that 12BH7s are not good preamp tubes? If so, would you mind elaborating on this a bit?

I have a preamp that is designed for 12AU7 tubes, but will also accept 12BH7s in their place. Is that substitution a bad idea?

 

[sparkie]

Did you mean to say that 12BH7s are not good preamp tubes? If so, would you mind elaborating on this a bit?

I have a preamp that is designed for 12AU7 tubes, but will also accept 12BH7s in their place. Is that substitution a bad idea?

They are more suitable to be an output tube on a preamp than a gain stage tube. But as far as micro-phonics, its not really an issue however they are prone to get noisy and microphonic if you mishandle them. Just like any other medium mu triode.

 

[Atriya]

They are more suitable to be an output tube on a preamp than a gain stage tube.

Because they can be noisy and/or microphonic, or some other reason?

 

[sparkie]

Because they can be noisy and/or microphonic, or some other reason?

its just like 12at7. they have good drive but they are microphonic when trying to use in a stage that not just a buffer. I wouldn't worry about it unless you trying to make a combo guitar amp or some powered monitors. Noise is more of a resistor and tube design than the tube itself.

 

[Atriya]

its just like 12at7. they have good drive but they are microphonic when trying to use in a stage that not just a buffer. I wouldn't worry about it unless you trying to make a combo guitar amp or some powered monitors. Noise is more of a resistor and tube design than the tube itself.

Thanks!

I'm not making anything: I'm just going to try replacing the 12au7s in the preamp sockets of my integrated amp, with a pair of Tung-sol 12bh7s. While the sockets specify 12au7s, the manufacturer says it can also handle 12bh7s.

 

[sparkie]

Thanks!

I'm not making anything: I'm just going to try replacing the 12au7s in the preamp sockets of my integrated amp, with a pair of Tung-sol 12bh7s. While the sockets specify 12au7s, the manufacturer says it can also handle 12bh7s.

if you just trying different tubes, try RCA 5963 tubes. They are my favorite series of 12au7. Either the white lettering or the red- orange ones labled RCA or Hewlett Packard.

The 12BH7 tungsol that came in a blue and white box, black plates wasn't bad as a phase splitter but had a very good balanced sound as an output transformer or innerstage transformer driver.

 

[Atriya]

if you just trying different tubes, try RCA 5963 tubes. They are my favorite series of 12au7. Either the white lettering or the red- orange ones labled RCA or Hewlett Packard.

The 12BH7 tungsol that came in a blue and white box, black plates wasn't bad as a phase splitter but had a very good balanced sound as an output transformer or innerstage transformer driver.

Interesting, thanks!

 

[jadedavid]

if you just trying different tubes, try RCA 5963 tubes. They are my favorite series of 12au7. Either the white lettering or the red- orange ones labled RCA or Hewlett Packard.

The 12BH7 tungsol that came in a blue and white box, black plates wasn't bad as a phase splitter but had a very good balanced sound as an output transformer or innerstage transformer driver.

Are your favorite RCA's Black plates or Grey plates?

 

[sparkie]

Are your favorite RCA's Black plates or Grey plates?

I like all of them. The results vary depending on the resistors in the circuit. If you find them tin can or edgy, then its not a good fit for the cathode resistor used. 12au7 RCA clear tops are nice, but they have to been stored correctly as they are prone to handling noise. The 50's 5963 RCA white streach lettering is a Telefunken build. The 60's RCa and hewlett packard red-orange lettering ones are Amperex. But most of your good sounding tubes will have a deep red and red-orange colored pins at the glass. New tubes use more copper in the pin material so they induce a small magnetic field that suppresses the harmonics from electrons radiating on the cathode and traveling in a vaccum (known in some circles as the Mikeska effect). Most of the time you can supress the magnetic field effect by using anton perry resistors in the grid and cathode circuit.

Home stereo gear is where nos tubes should be used more. as their subleties are not noticable in a band mix some applications where its in a stem or mixdown chain can help, but the bass harmonics generated are taken out if not suppressed in circuit. That is why you will see from time to time the pro audio using modern tubes over NOS tubes.

 

[jadedavid]

Thanks for the information. My question was primarily concerning the 5963 tubes.
I looked thru my stash and have found a number of different build construction techniques in them
Black plates, Grey plates, Square getters, Square getters with foil, Square hipped getters, horseshoe getters and halo getters.
Many are marked Beckman and I assume were intended for instrumentation usage.
Was not aware, and have not previously heard, that Telefunken made the early RCA 5963's and Amperex made the later "Orange/Red" lettered ones.

 

[sparkie]

Was not aware, and have not previously heard, that Telefunken made the early RCA 5963's and Amperex made the later "Orange/Red" lettered ones.

What is interesting is they made tubes for each other and for OEMs. So a RCA tube could be their own, an Amperex/Phillips/Westinghouse, a Mullard or a Telefunken depending on if and who they outsourced manufacturing. So like a RCA EL34 that is marked 6CA7 made in England with red letters was a black plate tube made by Mullard.

Tube manufacturers outsourced with each other either making the parts or the whole tube.or would collectively engineer a tube and one manufacturer make them all. The plates EI/Tesla in Yugoslavia made Telefunken 12a_7 tube plates. and the EL84 but also made the plates to assemble for Ton-sol back then. EI/Tesla had RCA make their EL34. But also back then Ton-Sol had Amperex make tubes so you will see Ton-Sol made in Holland was an Amperex build.