How To Spot a NOS 6L6GC Vacuum Tube

The most popular vintage NOS 6L6GC vacuum tubes are showcased in this video. Included are the rare KT66 and 350B types as well as RCA blackplates, GE, and Sylvania 6L6GC tubes. These tubes are very popular in guitar amps and tube hi-fi units, and good NOS versions are becoming very scarce.

[@audiotubes]

Hi, Those are great vintage tubes. The brown getter does indicate wear, but many in this condition still test good. As long as it tests OK on a gas test it will still operate fine if proper bias is set.

[@audiotubes]

Hi, The getter is an element that is "burned" inside the tube after it is sealed at the factory. This removes the last traces of air in the tube and deposits a metallic patch on the inside glass. This patch helps remove gas that may seep in over the years by oxidizing.

[@RestorationWatch]

The getter will turn white if you have a leak, and is a great sign the valve or toob is no good. Did you tell us how to spot a NOS? I have tons that I bought off the shelves back in the 80s. I also got stacks from older friends I made in the amplifier building cottage industry. I even made a all toob DAC with toob rectification, regulation and amplification using a 1K Caddock precision resistor as the load for the Burr Brown 20 bit DAC chips. Sorry for making fun of the word toob, I actually love it but we call them valves.

[@audiotubes]

The blue glow is fairly normal especially with vintage tubes used with high plate voltages. It is what little gas is in the tube being ionized by the high voltage. It does not harm the tube or your sound.

[@Movie-Tech]

@laterallateral They may have some value to vintage radio and audio collectors. NOTE: The 6L6G is NOT backwards compatible with the 6L6GC in most modern amp circuits as they have far lower maximum ratings than the GC does (this is also true for the metal 6L6, small-coke-bottle 6L6GA and the straight sided 6L6GB - they have identical ratings to the 6L6G).

[@audiotubes]

The terms refer to the "breakup" of the tube, or where it begins distorting. Soft is early breakup. medium is normal, and hard does not break up until the amp is playing VERY loud.

[@jonathanhorne6503]

I like to use Mullard EL37 tubes in my personal builds. My Ampeg B-15 clone currently is running a a pair.

[@Movie-Tech]

@lagus76 that is exactly what they are. The other give-away of a RCA-manufactured tube (regardless of brand) is the type number will be printed in a thick font within a similarly thick octagon, and the 'USA' is sometimes printed at the top of the octagon, and sometimes a dashed line will be below the octagon. the key is the thick dark gray ink that was used to print the type number on the tube - other manufaturers used the octagon but with a different font and thinner lines in the octagon...

[@glasstronic]

Cool vid, well done. My favorite are the Tung-Sol 5881Brown base. Bit surprised they weren't mentioned. Thanks for posting!

[@audiotubes]

The 300B cannot be used as a sub for the 6L6. My personal favorite power tube is the 350B but, as mentioned below, check with your amp tech or dealer to be sure your amp can use these in place of a 6L6 of any type.

[@tubical71]

Use 807 instead, as they are the bigger brother of the 6L6(GC) or hitachi´s 6GB8 (if you come across it) as you can have up to 4 of them for the price of a true RCA 6L6GC. Of cource you need to do some re-wireing as the 807 is different, (Top plate Cap). But they are both beam power tubes as well.

[@benjordan5567]

The GEC British KT66 tubes have a far greater heater consumption, 1.3 Amps rather than 0.9 for the 6L6GC. Some mains transformers might overheat, particularly if your amp has four of them, a difference of 1.4 Amps in total.

[@audiotubes]

Thanks for your comments. I am working on getting more shirts available, and will be doing more videos. No time to sit and get bored, that is for sure.

[@jspinks2388]

You forgot, the 70s Twin getter Tall Bottle Sylvania's....They are just Wicked Sounding... so Detailed/Smooth....Still have some....

[@audiotubes]

Yes, my bad there. For most applications in my experience the 350B has worked in place of 6L6GC tubes. I should have mentioned ALWAYS check with your dealer, tube technician, or manufacturer before you substitute power tubes, to make sure ANY substitue you wish to make (including the 350B) is acceptable and will not damage the amp or the tubes.

[@lucasmorales30636]

cuidados la impedancia d eplaca

[@mesa401]

The 6L6 GC tubes in my mesa boogie amp glow a pretty blue on the inside of the galss.

[@acatasus]

Thanks so much. I own four vintage amps, three of which are older than I am (I was born in 1947) and many of the tubes in these amps are tubes I bought from you. Your web site and your videos are a great education for me. Keep up the good work. By the way, I also have a few of your very cool tee shirts. Looking forward to your 12AX7 videos. How about 5Y3? Maybe something giving us ignorant folks a brief idiot's guide to tube amp circuitry would be nice (in your copious spare time, of course).

[@viscioushattermaid4410]

What’s the deal with those metal tubes? Can you use those in amps? Sound good?

[@bobbyohanesian4228]

Thanks for the videos

[@viscioushattermaid4410]

Ge or Sylvania for big blackface Fender cleans?

[@basspig]

The GE tubes tended to be gassy, handle less power and shorter lived. The Tung-Sol were pretty robust, as were the RCA branded 6L6's.

[@beverlyleano-bascos4051]

Sir is this tube can replace 6n9p Sir can you give me a suggestion i have a 6n9p do you think what tube can i replace them thankyou

[@Mr5150II]

i have the NOS Sylvania 6L6's in my peavey 5150 and boy, it screaamss now!

[@poikaa3]

Love this! good info! Thanks.... Wary of the 350B!

[@audiotubes]

I will probably have to make 2 or 3 videos to cover the 12AX7 tubes. Stay tuned!

[@dhisnadhamayanthi1135]

What is the maximum output power of 6l6

[@lagus76]

I have four 6L6 GC tubes in my Fender Bassman 100 that says "Made by RCA for Fender" They look like Blackplates. Do you know anything about that?

[@melvinsfan]

Great vid....any way one can be done for 12AX7's?

[@sjirk]

very cool video! thanks for sharing!

[@viscioushattermaid4410]

What’s better sounding? N.O.S. Sylvania or G.E. ?

[@TheNocturnalEvil]

It depends on your tonal preference. Philips-ECG Sylvania 7581A, STR-415, STR-387: They weren't normal 6L6GC tubes. They had a plate dissipation of 35-watt. The 7581A was a military issued tube that had thicker mica spacers than the civillian issued STR-387. The STR-415 was essentially a military issued 7581A rebranded for Mesa/Boogie. The 7581A, and the STR-415 had dual getters, while the STR-358 had a single getter. They were the cleanest and clearest sounding 6L6GC type tubes. They exhibited minimal distortion and compression. Their low end was deep, extended, and clear. Their mid-range was pretty neutral and detailed. They also had an extended, highly detailed, and clear high end, however their high end was never harsh because they exhibited minimal distortion even in the higher frequencies. They were the best tube for high gain amps due to their clear, detailed, and almost hifi nature. Due to their highly detailed and clean nature they never exhibited note smear. Circuits of some of the best American high gain amps like the Soldano SLO 100, Mesa Boogie Dual and Triple Rectifier, and Peavey 5150, were originally built around these STR tubes because those amps rely on their preamp section for high gain tones and require a perfectly clean power amp section. However, for blues players who like to overdrive their amps by cranking up the power amp stage the STR tubes aren't the most ideal choice. Their clean nature that makes them best tubes for high gain amps also makes them the worst tubes for blues players. They barely distort even if you crank them up loud. Philips-ECG Sylvania 6L6GC Short Bottle: They were the predecessors of the STR series tubes. Unlike the STR series tubes these short bottle 6L6GC tubes had a plate dissipation of 30-watt. They had a more mid-range than the STR tubes and also had lower headroom than those STR tubes. However their low end and high end wasn't anywhere as extended as the STR tubes. In some ways they were more flavorful than the hifi sounding STR tubes. They were the best Sylvania 6L6GC tubes for blues, but not the best 6L6GC for blues players. G.E. 6L6GC: They were 30-watt 6L6GC tubes. The biggest difference between Sylvania and G.E. 6L6GC tubes is that G.E. tubes were never as clean sounding as the Sylvania tubes. They had a nice harmonically rich warm tone with a deep but tight bass, warm mids, and a wee bit rolled off highs. They also exhibited a very smooth harmonic compression, and on higher volumes lent an almost liquid and syrupy quality to the guitar tones. They sounded huge, fat, and liquid. Alexander Howard Dumble absolutely loved GE 6L6GC tubes. However, their low end wasn't as extended as Sylvania STR tubes though, but then again you can't expect a 30-watt tube to have same level of low end extension as a 35-watt tube. G.E. 7581A: They were 35-watt military issue 6L6GC tubes built by G.E. to compete with the Philips-ECG Sylvania 7581A tubes. They were the most favorite tubes of Alexander Howard Dumble. They had all the qualities of the G.E. 6L6GC but their low end was as deeply extended as the Philips-ECG Sylvania 7581A. What made them so desirable was their unique harmonic response. They were rich in harmonics like the normal G.E. 6L6GC but at the same time they had a highly detailed harmonic response. They were rich in harmonics like the G.E. 6L6GC, but at the same time they never exhibited note smear just like the Philips-ECG Sylvania 7571A and were highly detailed. Due to this unique quality you could pretty much hear the harmonics produced by these tubes clearly in your guitar tone. The G.E. 7581A was the gold standard of 6L6GC for blues players. Amps loaded with G.E. 7581A tubes used to sing with complex harmonics. However, it's tough to find them these days. 1950-60 era Tung-Sol 6L6GC: This 30-watt 6L6GC tube is as rare as a hen's tooth. The best way to describe the old black top triple getter Tung-Sol 6L6GC will be the perfect evolution of a Tung-Sol 5881 on steroids. Its high end response was clean, detailed and defined like a Sylvania STR. Its low end response was big and clear, and was as deep as the G.E. 6L6GC. The most unique quality about the old Tung-Sol 6L6GC was its mid-range, it was throaty and thick like a 5881 but at the same time detailed and clear like a Sylvania STR. Another quality about these Tung-Sol 6L6GC was that they had even lower noise and microphony than the military issued Philips-ECG Sylvania 7581A, and G.E. 7581 tubes. Too bad finding them these days is almost impossible.

[@PlaneCrashClub]

whats ur opinon on some nos 6p3s soviet military tubes from the 50s. 20$ for 2 made in the folton factory basically a russian 6l6

[@davidb258]

What is a getter?

[@jspinks2388]

The 350b is far from plug in play for 6l6gc 1.6 heaters that's more into el34 or 6550/kt88 territory, and with any more modern plate/screen voltage it would melt down instantly lol

[@viscioushattermaid4410]

What tubes was Stevie using in the Vibroverbs?

[@jaysjaysgarden398]

RCA 6L6 GC Black Plates.

[@audiotubes]

@luigiperso Thanks for watching and stay tuned. More are on the way!

[@audiotubes]

Check out the 6550 / KT88 video. It could be done in 1 part. The 12AX7 video will probably have to be a 3 or 4 part series! Thanks for watching.

[@holdensaul8373]

i know Im randomly asking but does any of you know a way to get back into an Instagram account? I somehow lost my account password. I appreciate any tips you can give me

[@kingsleylangston1959]

@Holden Saul Instablaster ;)

[@holdensaul8373]

@Kingsley Langston thanks for your reply. I found the site thru google and Im trying it out now. Looks like it's gonna take quite some time so I will reply here later with my results.

[@holdensaul8373]

@Kingsley Langston It worked and I actually got access to my account again. Im so happy! Thank you so much, you saved my account!

[@kingsleylangston1959]

@Holden Saul No problem :D

[@audiotubes]

Fender used RCA tubes for many years. If your amp and set of tubes dates from the 1960s they are probably real RCA made blackplates.

[@sujathablockd9912]

audiotubes hubby

[@mikemac803]

I just managed to save a RCA 6L6GC Black plate tube from a physics department clear-out, do you have any idea how I could check to see if its still functional? Regardless it is a really cool decoration piece (one which lives next to my modern day Hi-Fi) I checked the date code and it came back as March 1964

[@lucasmorales30636]

tengo venta d e tubos, poseo algunos inconseguibles,, lo unico que no tengo es, 845 y 300b. estoy trtando d e desifrar una partida de tubos marcados como qtl ,pero es muy dificil, son nuevos,NOS

[@mayito714]

Do all guitar amplifiers that use the 6L6GC tube sound the same all things being equal? After all, an electric circuit only regulates voltage from a wall outlet does it not....

[@m.vonhollen6673]

Absolutely not! Different circuit designs, even different components, different component manufacturers, …. the slightest difference can affect the sound. The amp, the speakers, the speaker cabinets, the cables, ,.. everything interacts with everything else.

[@mayito714]

​@@m.vonhollen6673 Question 11 years ago was "All Things Being Equal". In other words, if we replace the RCA with a Sylvania will it sound the same?

[@ininper]

Thank you! :)

[@Movie-Tech]

@LeviMan2001 Metal 6L6 have far lower max ratings than the 6L6GC - you risk killing the tubes and your amp if you use them in an amp running a B+ higher than 350V.

[@lucasmorales30636]

tengo tubos nuevos d e metal 6l6 son par 19 w disipacion en placa el gc es para 30 watts,pero el metal posee muy buena calidad sonica,, por supuesto no pasar la potencia d e p laca¡ ni la tension,

[@dancingrizz]

RCA grey plates 4 me thanks.

[@Popaho]

😅😮