[Currawong]

An interesting thread from 2007 was bumped on this very subject.

Short answer seems to be: Stax in 1960 with the SRA-4S, as electrostats require a special amp:

http://www.stax.co.jp/OLD/Photo/SRA4S-1.jpg

but for dynamic phones, excluding pro gear with headphone outs, probably the Sure Solo-phone.

http://mysite.verizon.net/hirsch9000/shure1.jpg

After that, Grado designed the HP-1 for the HP-1000s just before HeadRoom started up business in the early '90s and the Melos SHA1 predates HeadRoom as well. HeadRoom created the first portable, of which the Desktop Portable is a descendant, and also the first balanced amp, the BlockHead, consisting of two mono amps in one box.

 

[bryanbhu]

That Stax one, I wonder how many/well/badly they sold back in its day?

 

[ericj]

I have seen on ebay a Koss amp for dynamic 'phones that claimed to be vacuum tube based, and was large enough to have been. Sold for much more than it was likely worth.

Mostly white in color. Much larger enclosure than either you have pictured. I don't recall anything further than that, but if it really was a glass amp that may make it older than the shure, certainly much older than the grado.

 

[HiGHFLYiN9]

Sorry for the graveyard bump but I think this is still relevant/interesting. I was looking into it and the Koss appears to be older; the (~1962) Koss A-1220. It's indeed vacuum tube powered. I think back in the day Hirsch found one. The Shure was somewhere around 1965.