LTA MicroZOTL tube upgrade

@troutstreamnm 

RE: Brimar vs. Mullard, it really depends on the exact tube types you are comparing. Both generally have the warm British sound.

As I've mentioned the triple mica black plate Brimar are wonderful tubes.

Many like the Mullard M8162. 

You can find some great Mullard 2-Mica CV4024 for about $25-30 each if you're diligent. Great tubes for the money. Later production (early 80's) is what you're most likely going to bump into as NOS tubes, but again, great value.

If you want something more geeky, rarer, altogether better, look for late 1950's Mullard Whyteleafe CV4024. Most folks are familiar with the Mullard Mitcham and Blackburn plants, but they had another one at Whyteleafe that just made superb tubes. Their factory symbol is a square with a line drawn diagonally through it. The 12AT7 produced there are exceptional. All of the normal characteristics of Mullards, beautiful mid-range, silky smooth highs, but also vey tight, disciplined control of the bass which is particularly unusual for Mullard tubes. The Mullard 10M 12AT7 is another nice one. I have some Mullard E81CC/6201 but they honestly haven't done too much for me. Valvo E81CC are better. Siemens, too.

Another delightful rarity are the early 1950s Philips Copenhagen 12AT7/CV455, etc. Very rare. But exceptional quality. These are often misidentified as Philips Herleen tubes because both plants use a triangle as their mark, but the triangles are different. If you pay attention to that you can scoop up some EXTREMELY valuable Philips Copenhagen Welded Plate 12AU7/12AX7 for a $100 or so when they are worth $1K+ because someone thought they were Amperex tubes.

If you wanna get geeky with your 12AT7, look into 7062 and E180CC. There are some very nice pinched waist examples of both out there.

Good hunting.

@tyray 

When you say GEC Version 1, what are you referring to? The tubes in the post that was linked are later 1970's 2-Mica production. If you see the four digit codes on the tubes like those the first two digits are the year of manufacture. Still nice tubes. 

But if you want to go after it, I recommend chasing some of the earlier production 3-mica tubes. Don't pay a premium for the CV-6091, I don't think there is any difference whatsoever. Not in my experience anyway.

@chickenoregg

I do have a source, in fact she explained the GEC A2900 tube to me this way. 

Thank you for your question regarding the GEC A2900 ECC81 / 12AT7.

The production code you referenced, 7838Z, indicates that these tubes were manufactured in 1978 (week 38). Based on this code, these are later-production GEC A2900s, not the early or “Version 1” examples from the 1950s–early 1960s.

That said, they are still genuine UK-made GEC A2900 tubes and represent very high-quality NOS production. Later GEC A2900s are known for excellent consistency, strong electrical stability, and very low noise, which makes them especially well suited for recording, phase inverter, and hi-fi applications.

While early A2900s are often sought after for their vintage character, many users actually prefer these later versions for their cleaner, quieter performance and reliability.

If you have any questions about how this tube might perform in your specific application, feel free to let us know and we’d be happy to help.

Best regards,

And these are NOS / NIB with seafoam blue lettering and lite cream background. But I would love to buy a couple off of you when funds and time permits and hopefully I can get some NOS / NIB with seafoam blue lettering and lite cream background or whatever you suggest at the time.

Funny, no one has ever brought this tube to my attention so I've never even heard of this tube before.Thanks, appreciate your help. I'll be in touch.

@tyray 

I think what she wrote is fairly accurate. The later generation 2-mica tubes have a very nice consistent tone. One of the biggest differences I have noticed is that they are much more balanced. Some of the early tubes are Charlie Sheen level off-balance. I have had a few pairs lately of NIB later production 2-mica A2900s and they have been great, I keep selling them though before I really get much time with them, Such is the life of a Tubesman. Keep in mind that GEC tubes can take quite some time to full burn in and mature to full bloom. Upwards of a year for the older tubes. They always sound great, but the older, almost used up ones are the best. I find this true of most tubes, I love listening to a tube that’s fully seasoned and peaking out. 

Keep in mind the A2900 is not a 12AT7. You can also sub it for a 12AX7. Gain wise, its smack dab in the middle of 12AT7 and 12AX7 (same as 5751). I had a pair of mono-blocked MC275s that called for four 12at7 and 3 12ax7 each, used 7 A2900s in each to glorious effect.

Here’s a link to a guy named Tom on Head-Fi. While I would be happy to help you, Tom’s prices cannot be beat if he still has tubes left. I cannot remember his story, but at some point, long, long ago, he came into a veritable grip of A2900s and meters them a pair or quad at time to those he feels deserve them. I think they are 360 euro for a NIB matched (possibly code matched pair). I have bought from Tom and can vouch 100% for him. He’s a stand up guy.

https://www.head-fi.org/classifieds/gec-a2900-ecc801s-e81cc-ecc81-12at7.10203/

Enjoy the roll.

@chickenoregg,

I actually did reach out to Tom-s at Head-Fi. And he kindly responded back and he had questions of shipping to the US with all the tariff stuff going on and we discussed that we’ll  take care of those issues when time and money permits. As I said earlier in a post, you tickled my fancy about those GEC A2900 tubes and that is a tube upgrade I know I’m going to pursue. Happy tube rolling indeed.