A question for the group

[KG0MN]

I am gathering the parts for a one tube transmitter that I saw the schematic for in the December 1938 copy of Ham Tips from RCA.  The transmitter  uses a single 813. Okay here is the question, I see one capacitor that is says is (1.5uuf PER METER).  I can't recall seeing capacitor with the "PER METER" description.  Can someone shed some light on what this means?

[K3ZS]

Probably wavelength, i.e. 40M band would be 60 pF capacitor (pF now instead of uuF)

[KG0MN]

Thanks a lot, that does make sense now that you point it out.

[W3RSW]

That 813 xmitter can be a real crystal cracker. Several mentions on this site previously. Use search function.  Be real careful when loading it up.

[W3GMS]

Not to discourage you from building what you want to build, but a MOPA which uses 2 tubes has many advantages.  MOPA's were around in the early 30's so it would be a very old time transmitter.  A MOPA stands for Master Oscillator Power Amplifier.  As Rick mentioned a high power one tube transmitter can be brutal on the XTAL.  With high XTAL current the XTAL will drift due to its internal heating. 

Joe, W3GMS       

[wa3dsp]

I think you are working from this schematic -

http://www.w7ekb.com/glowbugs/tx/813osc/813osc.htm

See the item labeled 'P'  - that is a 2V 50ma pilot light that protects the crystal from over current. It is very important to have that in the circuit and also to use larger crystals.

There was an article series several months ago in Electric Radio on this very subject.

[W9ZSL]

  A single 813 transmitter is scary.  One with an "Old Reliable"  6L6 isn't.

[AB2EZ]

I've built a number of single tube ECO oscillator/transmitters. In each case, I have also plate modulated them with an external modulator. I also helped a friend design one using a 6146, that he operates on 75m AM with an external plate modulator.

Bottom line:

I agree that these transmitters are very tough on crystals. Unless you use larger vintage FT-243 crystals, you will likely have problems with heating / overheating, and large amounts of frequency drift on key down. [My friend only operates on 3835, so he needs only one crystal that works okay in his 6146 ECO]

Unless your principal objective is to build that particular single tube / ECO transmitter, I agree with the advice in the other posts:

Build a transmitter with a separate 6CL6 (or 6AG7 octal tube equivalent) crystal oscillator, with regulated screen voltage ... following the design details given on Dr. Greg Latta's amateur radio web pages.

http://faculty.frostburg.edu/phys/latta/ee/6cl6xmtr/6cl6xmtr.html

If you want to operate on 7MHz or higher frequencies, you will need a tuned circuit at the output of the oscillator... coupled to the grid of the 813 with a 47pF capacitor. You need this because the input impedance ( grid-to- cathode) of the 813 is too low, at 7MHz and above, to produce a large enough 813 grid drive voltage swing, given the plate current swing of the oscillator.

Stu

[W9ZSL]

The December 1958 QST describes using a single 6146 for 50 watts.  It uses the 2 volt dial lamp in series with the xtl.  Does 80 and 40 Meters.  T-1 is 750 VCT at 150 MA.