> Which recieving tubes can be used for transmitting also?
> I've done it with a 6L6WGB, a 1U4 & a 3A5.
> Which tubes make good RF amplifiers? I'm not expecting a lot of power
> maybe 50 watts max. I've heard some sweep tubes can do up to maybe
> 200W in CW or SSB service.  I remember seeing a magazine article using
> a pair of 50C5's. Also heard of using 45 tubes but not sure what they
> would put out.
> 

Bob.... this is an interesting question.   It begs two answers.

1) any receiving tube of proper function can be used for transmitting
   AND VICE VERSA.  It really does not matter as long as ratings are
   not overdone, too much.  An '01A makes a fine transmitter as a Hartley
   oscillator. An 833 makes a fine regen detector and audio stage.
   ..... etc.  Generally, you want to rate the tube at the power required
   for the stage under consideration... with some safety factor (many times
   a factor of 2 or 3 is plenty).  Thus a 6L6 rated at 10 watts is a good
   choice, although they have been run to 150 watts by some lusty folks.
   An 807 rated at 35-50 watts is a good choice in that power class. 
   A 6V6 rated at 5 watts is a good choice in that power class.
   A 3A5 rated at 1 watt is a good choice in that power class..... etc.
   Hint..... tubes last longer and run cooler if you don't overrate them,
   and try to get 150 watts out of a 6L6.


2) certain tubes make better transmitting tubes, by convenience.
   For example, there are about 25 directly interchangeable tube types that
   will work in the above mentioned 6L6 socket (6G6, 6K6, 6L6, 6V6, 6W6, 6Y6,
   and a host of others of various commercial and industrial rating classes).
   If you design it for 160/80/40 use, they all will work, just fine.  If you
   push 10 or 6 meters, then you need to choose more carefully.
   Another example is the 50watter class tube.  You could use a 203, or a
   211, or an 845, or an 807, or an 832, or an 837, or a 6146 or a 6XXX sweep
   tube pretty much interchangeably, in rf amplifier service.   But, for good
   reasons of convienience, you might prefer to use a 6146 (cheaper, more
   plentiful, easier to neutralize, etc.).

Thus, it really boils down to......``it doesn't matter much what tube you
use, as long as you keep it in its ratings envelope for its class of service.''
Most receiver or audio tubes can be used at RF up to about 40 meters with
little worry.  Above that frequency, some tubes will require underrating
to keep from burning them up.  A good rule of thumb is to underrate your
tubes to about 3/4 of CCS RF (Continuous Class Service .... read AM) and
they will be very happy (as well as your tube budget).  ICAS RF (Intermittent
Class Amateur Service) usually pushes the tube more than I like, but that
is OK for short duty cycle applications like CW or SSB.

For 50 watts I would definitely stay AWAY from sweep tubes, unless someone
gave me a box of 100 each to play with.  I would much prefer and better trust
the good ol' 6146.  A pair of 807's does well at 50 watts.  Likewise a pair
of 1625's.  Don't push the 807 class tube (807 and 1625 and 837) to much
above 35 watts and they will run forever.  The 6146 is much more forgiving
at 50-65 watts.  Above 75 watts, even it will get a little tempermental. 

More emphasis should be placed on the selection of proper rf circuitry to
handle the power you are trying to generate.  Good choice of the proper
neutralization, proper biasing, proper bypassing, proper plate/screen
voltages and currents are much more important than the particular type
of tube used.

In the case of exotic rigs like self excited oscillator transmitters, it
is good to build a safety factor of 5 to 10 into the design.  Thus, use
a tube of 50 watt class (e.g., a 211) at a power input of 10 watts in
Hartley service, and it will be very stable, run cool, and not be so
subject to drift or chirp under heavy load.  The 6146, on the other
hand, can run with a xtal at 50-75 watts input quite well.  That type of
design factor is often overlooked when folks try their hands at exotic
rigs like Hartley oscillators or Dow oscillators.  A 50 watt Dow oscillator
should use a tube like an 813 rather than a 6146.  Dow's oscillator is the
classic high power electron coupled oscillator (he designed the ECO circuit
back in 1932).  Yet, you could use the Dow oscillator at 50 watts with an
813, followed by a pair of 813's for output to 250-500 watts.  The navy did
this sort of thing using 860's and 861's back in WWII and commercial folks
did it as early as the late 1920's in RMCA designs.  In amateur use, that
is much better handled by adding an extra stage such as a 6F6 or 6V6 or 6L6
Dow electron coupled oscillator followed by a 6146 or 807 buffer, followed
by one or a pair of 813's for output.  One 813 will idle nicely at 50 watts
output with about 500 volts on the plate, and run for 20 years.  You could
economize the design and use a 6146 oscillator at 300 volts on the plate,
followed by a 6146 buffer with 600 volts on the plate followed by a pair
of 813's at 600 volts on the plates and run a cool and comfy 50-200 watts
input by dittling a variac on on the plate transformer between 50% of 110vac
to 100% of 110vac.  The oscillator stage could be VR tube regulated with
105 volts on the screen and 315 volts on the plate (3 VR-105's) if desired
for greater stability, although that is usually not required on 160/80
meters.  On 40 it probably is required.  Thus several kinds of tubes could
be used, but convienience would dictate certain choices for generic playing.
If you were building a period rig, then use period tubes.  If you were
building a 50's/60's style rig, then use the later tubes for convenience
and ease of finding them in the junque box or the hamfest boxes.

Good Luck, and hope I have not bored anyone.  Others will have their preferred
tubes to use, but I suggest sticking with common proven types unless you need
to do otherwise.  Then keep within ratings by appropriate margins.

73/ZUT DE NA4G/Bob UP