1) holographic sound reproduction (amperex usa + telefunken / siemens germany + mullard gt britain + heerlen holland) 
2) long-listen full frequency w/ pleasant extension (heerlen holland + siemens germany + mullard gt britain + tesla czech) 
3) natural organic tone w/ flat mid band response (amperex usa + telefunken / siemens / valvo germany + mullard mitcham)
4) precision bass w/ depth and lush sonic resolve (heerlen holland + siemens / valvo germany + ei yugo + tungsram hungary)
5) warm musical dynamic sound reproduction (amperex usa / heerlen + siemens germany + mullard blackburn + bugleboy)
6) clarity w/ layered detail and subtle tone compression (telefunken / lorenz germany + tungsram hungary + tesla czech)
~
earliest '60s amperex are the top sonic echelon, revered for their incredible bass depth, euphoric airy ambience and transparency
these limited run 1961 production were only made 1-year, and replaced the dgetter variety for thicker richer mid-band euphony 
audiophile crown jewels, these selected screened-editions (ck/beckman) were special procurement orders to replace pq/mil issue!
this ensured high quality control, low noise, and audio grade phono ready mic certified for purer clearer sound reproduction
often compared to heerlen holland 'dutch house' sparkely resolve, '61 amperex usa produce more clarity w/ a crisper clean finish
this increase in peak resolution on early production types are sought after by listeners for immersive playback and vocal fidelity
the sound stage is quite linear and 3-dimensional, capturing vinyl style intimacy and pin-point warm bass is felt in your fingertips
as you can see w/ the attached sound curves, amperex tubes are reknowned for their scope and depth, quality and 10k hour life
all tubes are twice tested for mutual gm, audio grade circuit auditioned, and include amperex boxes + free postage!
~
7l6 *1j / 7l6 *1j same code ~ special ck screened selection ~ 120/120 ~ 118/124 % gm (65) also (14.9/14.9~14.2/14.2 gm mmhs)
7l6 *1k / 7l6 *1l ~ special beckman screened selection ~ 116/116 ~ 108/102 % gm (65) also (15.2/15.2~12/11.4 gm mmhs)
7l6 *1a ~ special rca sorted selection ~ 106/106 % gm (65) also (11.6/11.2 gm mmhs)
~
our life test is a key longetivity indicator, and our unique gm output test applies 225 vdc simulating actual circuit load
all tubes are also checked w/ an impeccable gas + leak/short check, and a proprietary complimentary refurb deox process
mutual gm conductance scores are the ability to transfer current ~ especially important for push-pull preamps
give 100+ session hours w/ your amps voltage to fully cure (breakin is important)
ships well packed worldwide, and free economy postage! 
~
~ authentic vintage hifidelity audio curation by caliacoustics ~
see our official site! limited editions, sealed-box true-nos rarities, and more collectibles