Made in USA by Tung-Sol.
Solid black plates with Triple O-Getter (one on top and dual on one side).
The first version from Tung-Sol. The Best 6550s ever made by Tung-Sol (USA). 

Used but tested good as new.

Made in USA by Tung-Sol (1950s).
Solid black plates with Single top Getter. Second version from Tung-Sol.
One of the best 6550s ever made by Tung-Sol (USA).
Great Power Pentode in the world.
Nos in box.

Made in USA by Tung-Sol (early 1960s).
Solid gray plate, no hole version with Triple O-Getter (one on top and two on each side).
One of outstanding 6550s ever made from Tung-Sol (USA).
Hard to find a nos nib matched quad at the moment. Only from us
Nos in box. Matched pair and quad are available. Tested under 3%.

Made in USA by Tung-Sol (1960).
Solid gray plate, no hole version with Triple O-Getter (one on top and two on each side).
One of outstanding 6550s ever made from Tung-Sol (USA).
Very hard to find today
Nos in box. Matched pair are available.

Made in USA by Tung-Sol (1967 - 1971).
Three holes on gray plate with Triple O-Getter. Last version from Tung-Sol ever made.
This version has been produced by General Electric in the same time and they are same quality and out looking. One of famous Power Pentode from USA.
Tested like new. Matched pair and quad are available. Tested very strong (under 4%).

Made in USA by General Electric (after 1980s)
If you want the best tone for your amp these are the tubes to get. An added benefit to having NOS GE 6550A is that these can handle much higher plate voltages and will last much longer in both Hi-Fi and musical instrument amps than most 6550 made today.
Nos in box. All same date code. Matched pair and quad are available. Tested under 2%.

Made in Holland by Philips (1954-1958)
Disc Getter. It is the best EL34s from Holland.  
Great bass control and sweet midrange, very musical. Highest performance.
Click here to see the difference bettwen Metal base EL34 Holland made and UK made.
Nos in original box. Tested matched pair are available. 5 tubes are in stock.