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.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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"Applied Control Theory for Embedded Systems" gives you just what it says.
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