LTA MicroZOTL tube upgrade

@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.

@chickenoregg Indeed, I am using 3 of the (early, 3 mica) GEC A2900 CV6091s in each of 2 Antique Sound Lab Hurricane DT monoblocks in the 6SN7 positions - - with (as you say) the suitable adapter.   Glorious sound.  Almost all of mine (I have 8 of them) are code SJ Z - September 1961, Hammersmith.  I fully second every word that you have written about these amazing tubes.