Tim Wescott wrote:
ken scharf wrote:
Tim Wescott wrote:
On Thu, 04 Dec 2008 06:23:48 -0800, JIMMIE wrote:

After years of avoiding morse code I am finally getting into it. the
ideal of operating a very simple transmitter appeals to my junkbox/
trashcan construction mentality.
I am looking for a substitue for a 6L6 that has the plate brought out
the top. I was trying to build a little Glowbug transmitter but was
having all kinds of problems neutralizing the the thing. I think I
would
have better luck if I can separate the grid and plate circuits from
each
other. I am considering an 807 as a replacement Suggestions would be
appreciated.

Jimmie

Dunno if it's been mentioned yet -- 2E26. The 807 is _not_ a 6L6 in
a different envelope -- it's quit arguably the 6L6's big brother, but
it's got different ratings; it could probably be shoe-horned into a
circuit designed for the 6L6, but you'd be missing out on about 6dB
of final output power.

The 807 IS a 6L6G with a 5 pin base and the plate connected to the top.
The published ratings of the 6L6G look different than the 807 because
of their intended use. ICAS ratings for the 6L6G were never published.
Also the 807 has additional shielding and insulation over the 6L6G
that make it usable at higher frequencies and voltages than the 6L6G.
Most 807's have ceramic spaces to support the plate which are lacking
in the 6L6G. But make no mistake about it, the two tubes share the
IDENTICAL cathode, grids, and plate structures.

The 6BG6G tv sweep tube IS an 807 with an octal base. It has the same
ceramic plate supports, but lacks the extra rf shielding.

The 1625 is an 807 with a 12.6 volt heater and a large (same as type
'59) 7 pin base.

The type 1614 is a metal tube based on the 6L6. It is a transmitting
version, and probably has additional shielding. Otherwise its internal
structure is the same as the 6L6 metal type.

The type 1619 is sorta kinda a 6L6 with a directly heated 2.5v cathode.
Same metal bulb as the 6L6. Specs' are different due to the different
element spacing thanks to the filament cathode. This tube is often
triode connected to replace 45's and 2A3's in old radios with a socket
adapter.

As a result the of the construction differences regarding shielding,
the 807 often would NOT need neutralization while 6L6G's and 6BG6G
tubes used as rf power amps do.


The 6L6GA was identical to the 6L6G except that the bulb shrunk from
an ST16 to an ST14 size. The 6L6GB was identical except for the bulb
changing again to a T14. The 6L6GC is a totally different bottle with
higher plate and screen dissipation and plate voltage ratings. The
6L6GC was said to be a plug in replacement for the older 6L6 tubes,
but RCA kept the 6L6GB around for a while anyway. In fact a bias
re-adjustment was a good idea when replacing an older 6L6 with the 'GC
version if a cathode bias resistor wasn't used.

I bow to your superior knowledge.

How do you know? Time spent busting tubes and looking inside? Old-time
service and/or circuit design experience? Experience building tubes?

I'd love to see a detailed family tree for some of the more popular tube
types.

I've done a lot of reading on this subject. Old QST's (from the '30s),
books about tubes, and I've smashed a few open (dead ones of course).
I also have a small collection of old tube manuals (in print and pdf off
the 'web).
BTW the 6L6 family tree is quite large and includes bottles such as the
7027/A (really a 6L6 with a bigger plate and TWO base pin connections
for G1 and G2). Most sweep tubes are descendants of the 6L6 (the 6BG6G
directly and others indirectly). Other 'hifi' output BP tubes such as
the 6550, and the 'KT' series are based on the 6L6 with larger elements
for handling more power. The British have in interesting twist on the
language. KT stands for 'Kinkless Tetrode' which refers to the lack of
the dip in plate current as the screen voltage reaches the critical
point of secondary emission in tetrodes. BP tubes are considered
tetrodes since they lack a third grid, but those BP tubes with beam
deflection elements should be considered 5 element tubes. (Not all BP
tubes have the deflection plates. The critical parts of the BP formula
are aligned turns on G1 and G2, critical spacing between G2 and the
plate, and optionally deflection elements to focus the electrons into
sheets. Having a plate with 'catch pockets' such as on the 4-400 works
as well as the BD elements.)