Are MULLARD NOS EL34s and LTA ZOTL40 REF worth the price of admission?

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" If you are looking to replace EL34 tubes, Mullard EL34 and TungSol EL34B are the go-to tubes. They are step up from the OEM tubes shipped with the amp, and will provide great tone."

https://www.tubesforamps.com/el34-6ca7-kt77-differences#:~:text=If%20you%20are%20looking%20to,and%20will%20provide%20great%20tone.
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My experience, I agree, new production, not pricey NOS.

In 1973 I inherited mono blocks made in 1958 with used but tested good original Mullard EL37’s in it (not EL34's), and a spare set of vintage Mullard EL37’s my uncle had ready to go,

I have bought new/collected old tubes for years, thus tried a variety of substitutes in those amps.

I also have used Fisher 500C and 800C receivers with various brands of 7591’s. There are differences, slight, and I have found, after research, the general descriptions of differences, i.e. more mids, firmer bass ... are correct.

I bought a Cayin amp, came with good 6550’s, sounded great, but, how would KT88"s sound in it? Bought the KT88’s, convinced myself I hear the expected slightly tighter bass. It could have gone the other way, came with KT88’s, try 6550’s, oh boy, those slightly better mids, .... i.e. how much do we convince ourselves?

OTOH, I have tried and hated a variety of 6sn7 tubes, clear differences, make sure your seller will allow returns after break in, like my favorite source

http://users.rcn.com/brentjes/bjtubes.htm

I think the ZOTLs need EL34 family tubes only. There's a review where they preferred new Genelex KT77.

I can’t say how NOS Mullard el34’s will sound in an LTA amp but I assure that xf2 NOS Mullards (both single and double getters) and the unicorn xf1’s are so much better than anything made today that the difference wont be subtle. $800 for a NOS quad is actually pretty fair. i wouldnt sell my xf2’s for $800.

You should call Andy at Vintage Tube Services. He'll help you figure tube related things out.

True did you convince yourself.Thats the thing with tube swapping your trying to find Oz...or Heaven.But it gives you something to do.