LTA MicroZOTL tube upgrade

@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.

Has anyone tried the National Union 6F8G round plate? I have 103db speakers that tend to be forward...thinking these might tame that 2-4K hump a bit?