807 output tube (the little magician)
V5306E%TEMP...@pucc.princeton.edu
"the Jan 807 was distinctly designed and made for RF transmission use which is
why we did not use them for VTL audio amplifiers."
Someone else on the net inferred that the 807 was only suitable for RF work.
This lead me to do some historical research on the 807 as regards applications.
Principally I relied on three sources of information. First was the RCA
Technical Manual TT3 published in 1938. Second was Sound Practices issue #2,
and third was DAvid Manley's book "The Vacuum Tube Logic Book" published in
1988.
According to an article in SP #2 the 807 was introduced in 1936. My 1938
TT3 manual clearly lists an audio frequency application for the 807 operating
in class AB2 with fixed bias. The introductory notes for the 807 states in
part:
"The resultant high power sensitivity makes this tube especially suited for use
as an rf or af amplifier..."
and:
"In class AB audio service two tubes of this type are capable of delivering
an output of approximately 80 watts."
This reference apparently is at odds with David's assertion thatthe 807 was
made distinctly for rf apps. J.Roberts in his sidebar feature of the little
magician (coined from RCA's propaganda in their 1941 Guide for transmitting
tubes) reprinted operating parameters from this manual which highlights
the operating parameters for triode connected 807's in Class AB1 push-pull.
Also reprinted in SP #2 was a set of plate curves for the 807 triode connected.
These guys (the RCA folks) must have been early audiophiles.
Roberts' sidebar also provides some interesting commentaries on the history of
the 807.
"It was a tube for many purposes. The 807 was rated for Class A, AB1, AB2, &
B audio service and class B and C RF amplifier service. It's mastery of many
disguises earned the 807 the title "The Little Magician" ..."
"Although they were used in many mediumppriced Pa amplifiers and in Altec and
Westrex commericial gear, the 807 was never as popular in home Hi-Fi gear as
other beam tubes like the 6L6, 5881, KT66, and 1614. Perhaps the exposed B+
on the plate cap argued against its use in the living room. It was specified
in American versions of the British Williamson design in lieu of the KT66 and
it was featured in some early heathkit and Grommes Williamson-type amps."
With the dwindling supply and rising prices of primo beefy output tubes nowaday
perhaps the 807 is due for a revival. Just keep cats and children away from tho
se plate caps."
Many of the early Williamson type amps which poularized hi-fi worldwide saw
fit to put the 807 to work. One that Joe left out and is a personal fave of
mine is the celebrated "musician's amp" designed by David Sarser and Melvin
Sprinkle and sold in kit form circa 1949.
Lastly here is a quote from David Manley's book published in 1988:
"The 6L6 GC and the 807 are closely related beam-power tubes with the 807 being
closer yet to the British KT66; so clsoe that the 807 was chosen by D.T.N.
Williamson for the American version of his historic amplifier. But to our ears
the 807 has no equal in its triode configuration."
There you have it. Historically this tube graced the topside of many notable
amps. To relegate it to mere RF service conflicts with this historical usage
of the 807 and many contemporaries are equally ablush with the sonic qualities
of the 807 tube.
David states in his post that the chinese built 807's were made heavier grade
and beefier in all respects. Whether or not that is actually the case (many
of the modern day made bombs in a bottle have promised heavier construction
and the like but I remain skeptical plus merely having thicker or bigger plates
does not insure the integrity of the metalurgy utilized in the plates or the
quality with which the tube is assembled) don't for a minute shy away from
using NOS 807 tubes if you should require their services.
In fairness to David he has brought up a very good point about current
tube manufacturing. David states:
"We're not saying all Chinese tubes are bad/good..." and "...it all depends
on which factory a given tube is built so you can't generalize the whole
country's output based on what you've seen from one factory."
True enough and I agree. The original post by Manley regarding the 807 did
in fact recommend the "Chinese" critters that are currently available without
specifying which factory one is good. Like I said in an earlier post of my own
my experience with the Chinese 807's was sonically dreadful. Perhaps mine came
from the wrong Chinese factory but pray god how in the world can the consumer
select the right Chinese 807 since no one marks their tubes with built in
factory A (or B,C,..etc.). Of course this is a disservice to the consumer whom
could more easily identify tubes of good manufacture if all tubes were approp-
iately labeled.
But David and EveAnna thanks for your observations and participation in RAHE.
Michael S LaFevre
Peerless/MagneQuest
Bob Breivogel
reveals that the internals are basicaly the same (down to the punch pattern
in the mica insulator.) The 807 appears to have added a bit of extra shielding
above the screen grid to reduce grid-plate capacitance, as well a bringing
the plate out the top for similar reasons, as well as to reduce RF losses
in the base.