Anyone have experience with the Tung Sol 7581a vs. EL34, KT66, KT88, 6L6

@wolf_garcia ,  I'm sure folks could charge me with ignorance or blasphemy here--  I think the 7581as sound better with less than 1000 hours on them.  I think they fade off just a touch in my system after that.  

So true Wolf.  

BTW,  I'll get the 7581as back in rotation again to see how they stack up to the GL KT77s.  Both are great tube compliments--I can't go wrong.

Have you tried the 7581a?

I bought my 7581a's from a guy in Ohio--cleveland area-on Ebay.  He tests them and does a 48 hour burn in.  They were so cheap compared to others I have bought.  I'm not rolling these out since rolling them in. 

Also, as my 6 year old likes to point out--they have a blue glow in addition to the traditional incandescent glow.  Very cool. 

Noromance, I'm curious to see if you like them.  I'm going to call upscale and ask Kevin why he doesn't stock these tubes.  

@rshak 
I bought them from this seller on eBay--here's a similar if not identical listing from her/him.

https://www.ebay.com/itm/Tung-Sol-Factory-Platinum-Matched-Quad-7581-7581A-6l6-type-tubes-24hr-Burn-...

I'm shy of 2 weeks into these tubes.  I have a good time running them in and with the holiday I was able to really let them run.  I'd say they have 40 hours on them now.  

To be honest, I think they changed a little but not too much from out of the box.  They "feel" like they settled in--yet that could be me getting used to them.  

I think these are more intimate in their presentation than the GL KT88, but not as bombastic or powerful.  They are not as shiny on top as the KT88 or as liquid as the EL34 in the midrange.  So what's to like? Much. 

These have an honest tweedy warm sound.  While the EL34 is--to my ears--sugary and heavy in a good chunk of the spectrum, this one is not but more so than the GL KT88.  What is odd and pleasing is that this one sounds better than the KT88 with percussion.  Snare drums really vibrate with the skin against the spring/rod or whatever they are made of.  Cymbal and strikes to percussion pieces of kit stand out--just a bit.  I liked that. 

The tube is not forward sounding to my ears.  There's a good chunk of energy pushing detail through.  

I'm going to get used to them more and then start rolling preamp/driver tubes through them to see what stands out, despite the swaps.  That should help me isolate their core characteristics. 

This is a fine tube and I am very pleased with it.  I'm still trying to figure out its fingerprint.  

Noromance, 

I agree!  I wish the 7581a could mate with an EL34 and have offspring.  The 7581a is near perfect for me--I just want a touch more of the EL34 midrange syrup. 

I finally tried the Gold Lion KT77s. Great tube. I think they are as good as the 7581. The GL KT88 was not as good in my setup. 

@slmccaul , I hear you!  I'm in the same boat.  Both of these are excellent power tubes, and are reasonably priced. Do you have the ability to try KT150s?  

After a long break from the 7581a tubes, I swapped them back in.  I was using Gold Lion KT77 reissues--great tube. 

The 7581a adds a bit of the power that the KT150 has and it seemingly has more headroom.  But, I say that without checking the specs.  That's how they sound.  

I remember now why I love these tubes. 

@frogman , How do you like the 7581as?  I recently sold my Primaluna and now have a Bob Carver Crimson 275, which runs (stock) KT120s.  I finally got around to trying the 7581as in it and they are really fun to listen to.  Great clarity and sweetness.