12AT7 NOS Tubes Shootout and Substitute for Hi-Fidelity (not guitar) Amp

I'm game-on to explore tube-rolling the 12AT7 preamp tube of my 300b amp. Seeking to try different 12AT7 NOS tube and 12AT7-substitutes (not 12ax7 or 12au7) to get some different flavor. I try to keep my mind open on different sounds. So far I have a GE 12AT7 and sounds midrangey. I want to try something else maybe a different brand or tube number with different sound. If you have any suggestions that would be great. Thanks...

The ’12AT7′ Tube
The 12AT7 is a miniature, high-mu twin triode designed for use as a grounded-grid radio-frequency amplifier or as a combined oscillator and mixer at frequencies below approx 300MHz. This tube has a mu factor of 60, as compared to the higher gain 12ax7 with a factor of 100, and the 12au7, with a mu of only 20. The 12AT7 is found in many high fidelity applications, as each triode section in normal use operates as a class A amplifier. They also turn up in line and microphone preamplifiers, musical instrument amps, and vacuum tube equipped recording equipment. By their design, they are inherently low noise, making them a good choice for these applications. The tube requires a noval nine-contact socket and may be mounted in any position.

DOUBLE TRIODE (separate cathodes)

B9A base pinout
Heater Voltage 6.3-12 V
Heater Current 300-150 mA
Plate Voltage 250 V
Plate Current 10 mA
Plate Resistance 10,900 Ω
Amplification Factor (μ) 60
Plate Dissipation (max) 2.5 W

 

Hey! finally something I can comment on from experience (sort of). I have Bottlehead Paramount 300B amps (the version with 12AT7 type drivers, I know they changed this later). The original kits came with ... ??? "pulls" or something that had been tested. Not sure what they were, I have them stored away so can't look. I got a McIntosh C220 preamp at that time, and things sounded a bit 'soft' for me. I got some used old stock tested good Tele ribbed plate 12AX7s for the C220, sounded better but I wanted more resolution/"crispness" to the sound. Got silver fuses ... yes, that did a little something. Got some Tesla NOS then new Gold Lion 12AX7s, which sounded the best of all, but still wanted something more.

I got some NOS Siemens & Halske triple mica 12AT7 types for the 300B amps ... YES, here was what I was looking for. Siemens & Halske E81CC - 1960s MINT NOS NIB 3-MICA 6201 Munich W. German Prem. ECC81 12AT7 - (Singles/M. Pairs/M.Quads/Trios) seems to be the last few of this batch (SAME ones I got years ago when he first got them!).

These charts (see below) are for 12AX7 and 12AU7s, from an old tube site ... but seems like the 12AT7 type S&H triple micas fit these descriptions very well (and I used the charts to pick out 12AX7 types for the C220 too). I think in general this is a pretty good 'chart' to look at for flavors ... I might try some others sometime as well, now that I have a SS Parasound P 7 preamp.





Of course, your amp may not 'respond' as the B'Head 300B amps do, but I hope so! The Bottlehead circuit is a bit unusual and uses 'modern' design, but the driver tube seemed to me to respond well to the change.

PS/edit: OOPS I see you said 'preamp' tube(s) ... my 300B amps have a 12AT7 as a driver tube. Possibly that's what you meant? or not. Anyway, still seems like the 'charts' might be useful.

 

I just ordered a backup matched pair of the Siemens tubes plus a MP of Brand New, MINT NOS NIB 1965-66 Brimar Military Production CV4024 12AT7WA tubes with Black Plates and copper posts. STC Production, Made in England. Very desirable 12AT7/ECC81 type tube for both Audio and Guitar applications. ... !!! His web page is now a PITA to put payment/shipping info into, but I've bought several tubes from him over the years (long ago). He's a good guy.

My amps are the 'original' versions of these Bottlehead Archives ... the newer ones (like on this archived page) use a different driver tube but the same topology. Mine do not have the soft-start circuit which was an upgrade offered later for mine ... I haven't had any issues so left it as-is. Great little amps. Upgraded coupling and 'parafeed' caps to V-Caps and Mundorf Silver/Oil. Have 'Princess' mesh plate 300Bs. All those didn't seem to change the sound much! As predicted by 'Doc' and Paul Joppa, but I had to try. The Siemens driver tube made a ... well not huge but clearly discernable upgrade to the clarity/resolution IMHO.

The Brimars I just got should be more relaxed and creamy ... we'll see!

PS/Edit: the text on the Bottlehead archive page is the same as with my original version, just with the new tube mentioned: "One half is configured as an actively loaded voltage amplifier using our Camille Cascode Constant Current Source for super quiet, dynamic, linear performance. The other half of the (now 5670, mine uses a 12AT7 type) operates as an actively loaded hybrid shunt regulator for the voltage amplifier, giving the driver stage great extension of both bass and treble information." My amps have this design/configuration, which I think is modern/possibly unique. I don't know if the 5670 is a direct replacement for the 12AT7 type? haven't looked into this, but the Siemens tubes work great in my amps, also looking forward to trying the Brimars for a different flavoring.

 

For years, a very common recommendation has been for the Mullard CV4024. It’s also financially realistic, even for a trial. The online tube boutiques would love to charge a fortune for these ... but there were just too damned many of them made.

EDIT: I crossed with @Rick58 ... but let me leave my comment alone as an independent vote for these.

 

Yes definitely.. I saw the link on the tube which I never even knew. Thanks. I heard some promising comments about the Mullards and Brimar. Someone said they have a nice bottom end with super clear high and lush midrange. I wanted to try it too and which reminds me of I have one tat I picked up long time ago. Ill try to get a matching one along the way. I'm pretty sure that the Brimar is the same. The packaging box seems the same too.

I'm not sure if this list will work as for a direct substitute.

12AT7 tube equivalents
Special thanks to Brent Jessee Recording & Supply, Inc.for kindly granting Effectrode permission to reproduce the following material below.

• 12AT7: This USA manufactured tube has wing shaped plates. The early versions have blackplates (later versions have greyplates) with a square or D shaped top getter at the top of the envelope. All are great tubes, and the finest (like the RCA black-plates) are on par with the military and industrial versions. Sometimes “selected” versions of this tube turn up. Often made by large manufacturers like RCA, they are usually labelled with the brand of the product they were selected for. Most often electronic organ brands are found on the label like Baldwin, Wurlitzer, and others. Sometimes hi-fi and musicial instrument amps had select tubes made for them, and labels like McIntosh and Fender turn up. The tips of these tubes are usually painted a color, indicating they have been screened for low noise.
• 12AT7WA: This is a military version of this tube, and may also be listed as a 6201. Some tubes have both type numbers on the label. These usually have thick mica spacers. The RCA versions have extra support posts and tiny “12AX7″ type plates, nearly always black. This tube is usually very low in microphonics due to it’s rugged construction.
• 6201: Frequently, this number appeared along with 12AT7WA (military version) on the same tube. However, some brands made the 6201 as an “industrial” 12AT7. Sylvania made a 6201 in their Gold Brand line, and it came in the distinctive gold box, had gold lettering on the glass, and most (but not all!) had gold plated pins. Amperex made a very nice PQ version of the 6201 with gold pins. A few 6201 tubes, usually early ones, have an extra mica spacer on top, known as “triple mica”, and are noted for lower microphonics. Overall, this tube is a step up from the standard 12AT7, and most were made to meet military specs so that both military and industrial versions could be manufactured on the same assembly line.
• 6211: This unusual tube is listed as a frequency halfer, in addition to being a class-A amplifier dual triode with medium mu. Medium mu means it has lower gain than the typical 12AT7, in fact lower than even the 5965 listed below. It also has much larger, flat plates that have diamond shaped points at the corners bent inwards (in the versions I have seen) that seem to add rigidity to the plate structure. This tube also has slightly lower plate voltage and current ratings
• 5965: This industrial tube is close enough to the 12AT7 that audiophiles have started buying them up and commenting on the low noise of this tube. It most likely is because it has a lower gain, a mu of 47 compared to 60 of a 12AT7. It is kind of like using a 5751 in place of a 12AX7–the lower gain being the main difference. These tubes are still plentiful, and are really well made. GE made a fine version of this tube in their “5-Star” broadcast line. A few have an extra mica spacer on top, known as “triple mica” and noted for lower microphonics. There is also a rare Telefunken version of this tube with long plates.
• E180CC or 7062: Most often found in European types, typically Amperex or Philips, this tube is virtually the same as a 5965 in regard to electrical specifications. Audiophiles have been seeking it out since the price is generally lower than the premium ECC81 N.O.S. prices currently. Like the 5965, it has slightly lower gain than the 12AT7, and has the added advantage of a 10,000 hour heater life to make it another audiophile “secret” tube. A super bargain when you find them, since they are musical and smooth to listen to, and actually sound better than many standard 12AT7 tubes. This tube is about a half-inch taller than the standard 12AT7, so chassis space is an important consideration.
• 6414: An industrial, computer rated dual triode, virtually the same specs as the E180CC or 7062 listed above. Unlike the E180CC, this tube was made in the U.S.A. It is a more rugged build, with the Raytheon black-plate type sporting triple mica and military ratings. This tube is also like a 12AV7 and will work wonders in any 12AT7 spot, and may be just the ticket if you want to boost the gain of a 12AU7 circuit. The 6414 is getting very hard to find, but with a 10,000 hour heater rating you may never need a replacement. Discussion groups rate this type very highly for use in headphone amps. Stands about 1/2 inch taller than the standard 12AT7.
• 6829: Yet another industrial tube that is very similar to the 5965. This one has a mu factor of 47 so it is slightly lower than the typical 12AT7. Those I have heard are rich, detailed, warm, and thanks to the lower mu, very quiet and low in microphonics. GE made these in their 5-star and military line so they are a rugged and long lasting tube. Like the E180CC, this tube is about a half-inch taller than the 12AT7. An excellent audio bargain now, but prices may soon climb as audiophiles discover them!
• 6679: This is an industrial 12AT7 designed for mobile communications use. It maintains it’s output even if the filament voltage varies. Nice tubes, but they never have been too plentiful. They will work fine in hi-fi use, and are a step up in quality from the standard 12AT7.
• 7728: This was a high-end industrial tube made by CBS or Hytron (same factory made both, actually) with gold pins. Very scarce.
• ECC81: This is the European version of the 12AT7, and is identical to it. The Telefunken even has the wing shaped blackplates, just like the RCA. Great tubes, equalled only by the RCA blackplate or the military/industrial versions. Even those made for U.S.A. hi-fi products in the 1960s (Knight, Bogen, Daystrom, Dynascan, etc.) are excellent tubes, and have the fine sound quality of those with Mullard, Amperex or Telefunken labels. The rarest are the 1950s versions of Mullard and Amperex with a “D” shaped top getter.
• E81CC or ECC801S: This is a rare tube, usually found only in the Telefunken or Siemens brand. These tubes have been screened for audio use and low noise, and have a 10,000 hr. rated life on the heater. The ECC801S are by far the rarest, and the E81CC only a little more common. Both are excellent, low noise, finely crafted tubes, with the E81CC being the best value currently when compared to the recent spiraling rise in the ECC801S prices. They are both rare, but if you find some they may well be the last 12AT7 tube you will ever need to buy!
• CV4024 and M8162: Fine British military tubes from the 1960s and early 1970s. I have seen mostly Mullard examples of these, although Brimar did make some. Depending on the manufacturer, the tube may have both numbers on it. The rarest and best are the early Mullards labeled with M8162 and the shield logo. Most of the Mullard military tubes were made at the Mitcham, UK factory, which made most of the British military tubes.
• CV455: Another British military type of 12AT7. Usually Brimar was the maker of this fine tube, with the earlier versions from the 1950s being the most desirable. Watch for the versions made in the 1970s. These have wing shape black plates and a sound close to the earlier type, at often half the price!
• 6060: This rare tube is the Brimar answer to the Genalex A2900. It has a similar construction to it. These are sometimes called the “Yellow-T” tube due to the large capital letter “T” in a yellow triangle on the glass. The best of these were made by Brimar at their Footscray, UK factory in the 1950s. Virtually all of these are phono grade, they are very quiet. There are later versions with the “T” logo on a white triangle, but these are not as desirable, sonically, and when found should not be nearly as expensive.
• A2900: The even scarcer A2900 is in the “Gold Monarch” series by Genalex. Genalex was the premium line of tubes produced by the Marconi-Osram Company in England. It has wide, flat black plates and white lettering on the glass, the words “Gold Monarch” in white script, with the red Genalex decal logo around the top of the tube. There is also a British domestic version with the grey and blue GEC decal on the glass, that was not exported. These are true audiophile tubes, with tightly controlled noise specs, designed with audio perfection in mind. Any scarcer and these would be museum pieces!

 

I was gonna mention Brent Jessee too ...! he seems to have all the 'exotic' NOS types! fun stuff.

ACK, seems like his site https://www.audiotubes.com/ is kaput or something, dang. Maybe it's just having maintenance or something, his site always is entertaining to read thru. I see he has eBay sales too but it's not the same. Oh well.

BTW, TubeMonger says he has more of the Siemens tubes at his European partner site. I guess he only has 12 or so left at his US location. Apparently he bought >1000 of them in the batch described (years ago); he said there's plenty left if I/we want more. I think one more pair will do for me! So that's good news for others, they're great high resolution tubes IMHO. He did say the Brimars have 'that British midrange' which may or may not be different than what you already have.

 

Wow, Jim, that's quite a system you have there! and dang! Classic Car Guy, now I might have to try some other ones !!!

 

You want west-German Teles. All other AT7s I tried were inferior, including Mullards.

 

Valvo Blue Label 6201 12AT7

 

I'm not so sure if they are direct fit. the pin assignments are correct beside a slight difference in the plate voltage. MU are quite close.

what preamp/amp did you put it on?

interesting.. How does it sound? I know those are difficult to find...

 

********Update on this 12AT7 tube equivalent********
"Like what I mentioned on the previous review that I'm not sure if this list will work as for a direct substitute."

The ones that are marked red is NOT a direct (drop-in) substitute.
The ones that are marked green is a direct (drop-in) substitute.
The ones that are marked orange is still in process for I don't have the data sheets yet.

12AT7: This USA manufactured tube has wing shaped plates. The early versions have blackplates (later versions have greyplates) with a square or D shaped top getter at the top of the envelope. All are great tubes, and the finest (like the RCA black-plates) are on par with the military and industrial versions. Sometimes “selected” versions of this tube turn up. Often made by large manufacturers like RCA, they are usually labelled with the brand of the product they were selected for. Most often electronic organ brands are found on the label like Baldwin, Wurlitzer, and others. Sometimes hi-fi and musicial instrument amps had select tubes made for them, and labels like McIntosh and Fender turn up. The tips of these tubes are usually painted a color, indicating they have been screened for low noise.

• 12AT7WA: This is a military version of this tube, and may also be listed as a 6201. Some tubes have both type numbers on the label. These usually have thick mica spacers. The RCA versions have extra support posts and tiny “12AX7″ type plates, nearly always black. This tube is usually very low in microphonics due to it’s rugged construction.
• 6201: Frequently, this number appeared along with 12AT7WA (military version) on the same tube. However, some brands made the 6201 as an “industrial” 12AT7. Sylvania made a 6201 in their Gold Brand line, and it came in the distinctive gold box, had gold lettering on the glass, and most (but not all!) had gold plated pins. Amperex made a very nice PQ version of the 6201 with gold pins. A few 6201 tubes, usually early ones, have an extra mica spacer on top, known as “triple mica”, and are noted for lower microphonics. Overall, this tube is a step up from the standard 12AT7, and most were made to meet military specs so that both military and industrial versions could be manufactured on the same assembly line.
• 6211: This unusual tube is listed as a frequency halfer, in addition to being a class-A amplifier dual triode with medium mu. Medium mu means it has lower gain than the typical 12AT7, in fact lower than even the 5965 listed below. It also has much larger, flat plates that have diamond shaped points at the corners bent inwards (in the versions I have seen) that seem to add rigidity to the plate structure. This tube also has slightly lower plate voltage and current ratings
• 5965: This industrial tube is close enough to the 12AT7 that audiophiles have started buying them up and commenting on the low noise of this tube. It most likely is because it has a lower gain, a mu of 47 compared to 60 of a 12AT7. It is kind of like using a 5751 in place of a 12AX7–the lower gain being the main difference. These tubes are still plentiful, and are really well made. GE made a fine version of this tube in their “5-Star” broadcast line. A few have an extra mica spacer on top, known as “triple mica” and noted for lower microphonics. There is also a rare Telefunken version of this tube with long plates.
• E180CC or 7062: Most often found in European types, typically Amperex or Philips, this tube is virtually the same as a 5965 in regard to electrical specifications. Audiophiles have been seeking it out since the price is generally lower than the premium ECC81 N.O.S. prices currently. Like the 5965, it has slightly lower gain than the 12AT7, and has the added advantage of a 10,000 hour heater life to make it another audiophile “secret” tube. A super bargain when you find them, since they are musical and smooth to listen to, and actually sound better than many standard 12AT7 tubes. This tube is about a half-inch taller than the standard 12AT7, so chassis space is an important consideration.
• 6414: An industrial, computer rated dual triode, virtually the same specs as the E180CC or 7062 listed above. Unlike the E180CC, this tube was made in the U.S.A. It is a more rugged build, with the Raytheon black-plate type sporting triple mica and military ratings. This tube is also like a 12AV7 and will work wonders in any 12AT7 spot, and may be just the ticket if you want to boost the gain of a 12AU7 circuit. The 6414 is getting very hard to find, but with a 10,000 hour heater rating you may never need a replacement. Discussion groups rate this type very highly for use in headphone amps. Stands about 1/2 inch taller than the standard 12AT7.
• 6829: Yet another industrial tube that is very similar to the 5965. This one has a mu factor of 47 so it is slightly lower than the typical 12AT7. Those I have heard are rich, detailed, warm, and thanks to the lower mu, very quiet and low in microphonics. GE made these in their 5-star and military line so they are a rugged and long lasting tube. Like the E180CC, this tube is about a half-inch taller than the 12AT7. An excellent audio bargain now, but prices may soon climb as audiophiles discover them!
• 6679: This is an industrial 12AT7 designed for mobile communications use. It maintains it’s output even if the filament voltage varies. Nice tubes, but they never have been too plentiful. They will work fine in hi-fi use, and are a step up in quality from the standard 12AT7.
• 7728: This was a high-end industrial tube made by CBS or Hytron (same factory made both, actually) with gold pins. Very scarce.
• ECC81: This is the European version of the 12AT7, and is identical to it. The Telefunken even has the wing shaped blackplates, just like the RCA. Great tubes, equalled only by the RCA blackplate or the military/industrial versions. Even those made for U.S.A. hi-fi products in the 1960s (Knight, Bogen, Daystrom, Dynascan, etc.) are excellent tubes, and have the fine sound quality of those with Mullard, Amperex or Telefunken labels. The rarest are the 1950s versions of Mullard and Amperex with a “D” shaped top getter.
• E81CC or ECC801S: This is a rare tube, usually found only in the Telefunken or Siemens brand. These tubes have been screened for audio use and low noise, and have a 10,000 hr. rated life on the heater. The ECC801S are by far the rarest, and the E81CC only a little more common. Both are excellent, low noise, finely crafted tubes, with the E81CC being the best value currently when compared to the recent spiraling rise in the ECC801S prices. They are both rare, but if you find some they may well be the last 12AT7 tube you will ever need to buy!
• CV4024 and M8162: Fine British military tubes from the 1960s and early 1970s. I have seen mostly Mullard examples of these, although Brimar did make some. Depending on the manufacturer, the tube may have both numbers on it. The rarest and best are the early Mullards labeled with M8162 and the shield logo. Most of the Mullard military tubes were made at the Mitcham, UK factory, which made most of the British military tubes.
• CV455: Another British military type of 12AT7. Usually Brimar was the maker of this fine tube, with the earlier versions from the 1950s being the most desirable. Watch for the versions made in the 1970s. These have wing shape black plates and a sound close to the earlier type, at often half the price!
• 6060: This rare tube is the Brimar answer to the Genalex A2900. It has a similar construction to it. These are sometimes called the “Yellow-T” tube due to the large capital letter “T” in a yellow triangle on the glass. The best of these were made by Brimar at their Footscray, UK factory in the 1950s. Virtually all of these are phono grade, they are very quiet. There are later versions with the “T” logo on a white triangle, but these are not as desirable, sonically, and when found should not be nearly as expensive.
• A2900: The even scarcer A2900 is in the “Gold Monarch” series by Genalex. Genalex was the premium line of tubes produced by the Marconi-Osram Company in England. It has wide, flat black plates and white lettering on the glass, the words “Gold Monarch” in white script, with the red Genalex decal logo around the top of the tube. There is also a British domestic version with the grey and blue GEC decal on the glass, that was not exported. These are true audiophile tubes, with tightly controlled noise specs, designed with audio perfection in mind. Any scarcer and these would be museum pieces!

 

I have a 300b SET amp that is very good in bottom end and high, midrange is 3d excellent. I'm very satisfied with this amp.
I have another 300b push-pull amp that is just good in bottom end, more "midrangey" (in a way that I want to suppress it a bit) and very good high. This amp is more fast and precise not like the set amp which I can also use it as a rock and roll amp. I'm thinking that is may need to have preamp circuit dialed to the sound that I want it and I know it will take a while to get it right. So before I do that, I wanna try a different tube first and see if I can at least get it close to where I can acquire the sound.

 

AVA Fet Valve CFR preamp.

 

"It's only money." Or "You only live once." Or "Get 'em while you can." Or any other audiophile rationalization you can come up with.


(2) NOS TELEFUNKEN ECC801S 12AT7 VACUUM TUBE | eBay

 

Well, in my view it’s Telefunken as well. And if you really really can’t get them or are too stingy,
then buy Siemens. None else. And they live longer as far as I heard it. Mine never broke or
were used up.

Except that my HiFi friend downstairs swears that very old long bottle Valvo are the best.

I am sorry, but never any US Tube (also no Jap) have reached even Siemens level, and I tried
my best with RCA Black Plates from 1950 (in this case it was ECC 83 though) - muddy sound

 

I have a pair of NOS Tesla E83CC (long story, but seemingly the same tube/parts as the Tele ECC803S), wondered if there was an equivalent 'E81CC/ECC801S' version, seems not. Came across M. Pair USED E81CC ECC81 Triple Mica Goal post sup. Siemens German Valve Tubes | eBay (A2900 British domestic version) if anyone is interested. Of course assume they're actual drop-in replacements or at least will work properly (enough) in the circuit/installation.

Seems like some of these 'iffy' ones are only physically different? or are there operational parameters that are different enough they may not perform the same? I assume that is the case ...

BTW, to me, the NOS Tesla E83CC (= Tele ECC803S?, at least as close to those as I'll ever come!) sounded very good, maybe better than the used ribbed plate 'regular' Tele 12AX7 types I had in my McIntosh C220, but nothing really special. Got some new Gold Lions, they sounded the best (and all virtually identical in character). Maybe in my upgraded system I'd be able to tell the difference, alas, I don't have the C220 any more.

Not to say the Tele ECC801Ss above aren't the cat's meow, and the $285/pair seems not unreasonable, but I think I'll stick with my triple-mica Siemens (for clarity in sonics) and try the Brimars for a little of the 'British midrange'.

 

This is one of the set that I haven't tried and its 20 years old in my possession. I have a 12ax7 version of this installed in my Marshall amp and its up there. In fact I never even changed that tube since 1998. As soon as I get the rest of the 12at7 that I'm buying, Ill try each one for 2 weeks each and Ill try putting this set in line. I wanna break in the new push-pull amp first for I only have less than 100 hours of use in it.

 

I got a lot of tubes coming over. These are smooth plate germans. Hopefully it'll bring some shine.

 

Any news on your new 12AT7? Still waiting for mine too.

 

On your 12at7wa are the black plates rounded and crimped on each side or is it boxed with 3 holes on he left side? How is it on bass and highs?

I found the right combination on my other 300b PP amp. Since this acme output tubes has a bassy, airy and warmth sound, I am very happy using the 12at7 Raytheon preamp large black plate 12at7 tubes that gives me a shimmering highs, lush midrange. Combining the two is a nice bassy, holographic 3d sound. Highly detailed sound. My biggest remark is "A lot of BASS" and for 3 weeks of everyday use, perfect. I didn't have to adjust anything on my EQ.
Also
Im trying to get the right tube combination of my other Psvane 300b (regular only copy of WE300b st bottle). That one is a bit more vocal, sharper highs and less bass than the acme. Trying to explore more on getting a 12at7 large grey plate.. It can be a 6201 or a 7062 / E180CC (not proven if a direct substitute on my amp). Its quite interesting to try it if Ijust know. Any takes??

 

I’m sorry it’ll actually be a while before I will be swapping in the new tubes. I’m just setting things up and don’t want or need to change tubes at this time. What I wrote does sound like I was enthusiastic to try the new flavors, that’s true but ... I think now I’ll be leaving things as is for a while.

I’ll have to look at them to answer your other questions.

 

I like any RCA 12AT7.

 

what kind of RCA in plate material and sound?
thinking about trying the 7062 / E180CC. There is a difference in plate voltage.

 

In my Ampex preamp I like the GE 6201 with the green lettering. They are very quiet, clean, and have a very forward vocal presentation. I use this preamp exclusively for CD listening through headphones.

 

The past 4 days I haven't really paid attention to my amp for I was running low volume while working and using a streamer. I notice that there is a slight harshness sound coming out on the left speaker. I thought it was just the streamer for I been listening to personal hi fidelity recordings for months and months till I toned down.
Anyways I started listening loud again which I normally do and there is a horrible popping sound that's coming out of my left cabinet that sounds like I blown the speakers for years of pushing it and sounded like it lost its integrity and energy. I was almost gonna get a woofer exact factory replacement till I thought about checking the preamp tube....
Guess what. It did it again and I blew another 12at7. It was 50% microphonics. Damn...This always happen to my favorite Raytheon 12at7 black plate. Now I'm down to 3 left. I don't know whats going on with these tubes. From brand new, sometimes I get 1 year, sometimes 5 years or so... If I use a different brand, no problem. In fact I have a mu mullard backup kicks and had it since 2004 running perfect.