I've been doing a lot of research on the various pulp heroes, and I see a lot of people talking about pulp heroes who are known to be public domain, but for the life of me, I can't find any kind of list anywhere on the internet that attempts to separate the public domain characters from the ones that are still under copyright. Below are some of the characters I've researched and I'm trying to get a definitive answer on whether they are public domain and why they are. Can anyone offer me any info on these characters or point out others that are certainly public domain?
Magazine appears NOT renewed:
CAPTAIN HAZARD by Sam Gordon Gurwitt (1890-?) in Nickle Detective (March, 1933)
CAPTAIN HAZZARD by Paul Chadwick (aka Chester Hawks, 1902–1972) in Capt. Hazzard Magazine (May, 1938)
CAPTAIN ZERO by G.T. Flemming Roberts (1910-1968) in Captain Zero (1949)
THE COBRA by Richard B. Sale (1911-1993) in Ten Detective Aces (1934)
JIM ANTHONY, SUPER DETECTIVE by Victor Rousseau Emanuel (1879-1960) in Super Detective #1 (October 1, 1940)
LONE EAGLE by F.E. Reichnitzer in Lone Eagle, Fighting Ace #1 (September, 1933)
MOON MAN by Frederick Clyde Davis (1902-1977) in Ten Detective Aces/Detective-Dragnet (June 1, 1933)
RED FALCON by Robert J. Hogan (1897-1963) in Dare-Devil Aces (1933)
SECRET AGENT X by Paul Chadwick (1902–1972) in Secret Agent X #1 (February 1934)
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Magazine appears not renewed, but story might be, due to popularity:
BLOND ADDER by Lester Dent (1904-1959) in Ten Detective Aces (1933)
G-8 by Robert J. Hogan in G-8 and His Battle Aces #1 (October 1933)
GOLDEN AMAZON (Violet Ray) by John Russell Fearn in Fantastic Adventures (July 1939)
GREEN GHOST by Johnston McCulley (1883-1958) in Thrilling Detective (Mar 1934)
MASKED RIDER by Oscar Schisgall (1911-1984) in Masked Rider Western Magazine (April, 1934)
OPERATOR 5 by Frederick Clyde Davis (1902-1977) in Operator #5 #1 (April 1934)
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Magazine possibly renewed, but uncertain:
PROF. I.V. FROST & Miss Jean Moray by Donald Wandrei (1908-1987) in Clue Detective Magazine (1934)
SEVEN FOOT SAUNDERS by William Verne Athanas (1917-1962) in .44 Western Magazine (June, 1950)
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Magazine apparently renewed, but character appears to have been used unlicensed:
BILL BARNES by Monty Montayne and Chuck Verral (aka George Eaton) in Bill Barnes, Air Adventurer v1 #1 (February 1934)
DR.THADDEUS HARKER by Edwin Truett (1904-1945) in Detective Dime Novels/Red Star Detective (1940)
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Magazine and story appear to be likely renewed:
CAPTAIN SATAN by William O'Sullivan in Strange Detective Mysteries/Captain Satan (1938)
CAPTAIN V by Ralph Oppenheim (1907-1978) in Battle Birds Magazine (1942)
CRIMSON CLOWN by Johnston McCulley (1883-1958) in Detective Story Magazine (Jul 31 1926)
DOCTOR SATAN & Ascott Keane by Paul Ernst (1902-1985) in Wierd Tales (August, 1935)
GREEN GHOST by G.T. Fleming Roberts (1910-1968) The Ghost (Winter 1940)
SCARLET FOX by Eustace H. Ball (1881-1931) in Black Mask (January 1, 1923)
SECRET SIX by Robert J. Hogan (1897-1963) in The Secret 6 (1934)
SKULL KILLER by Ejlar and Edith Jacobson (aka Randolph Craig) in The Octopus (February 1939)
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Pulp Characters that I'm pretty positive are under copyright:
The Avenger
Captain Future
Doc Savage
The Shadow
The Whisperer
Of the above, I'm almost certain Secret Six and Golden Amazon are also under copyright.
Subject: Various Pulp Heroes 
