FT 243 Crystals and others.

[Kenneth G. Gordon]

On 27 Feb 2007 at 21:44, Bry Carling wrote:

> >  from shattering when used with an old cathode keyed novice 
> > transmitter like the DX20 or something like it?
> > 
> > mike
> 
> Hello Mike - they are in use in hundreds of ham transmitters and
> generally do not fail.

Agreed. Unless the transmitter involved is HORRIBLY out of 
adjustment, or there is some other problem with it, there should be 
absolutely no problem using them.

> Some extensive tests were done by materials science 
> professor, Dr. David Gordon-Smith, G3UUR a couple of 
> years ago and documented in Electric Radio Magazine.

This is the article I mentioned. I thnk the maximum current he tested 
through those crystals was 300 mA.

<snip> 
> the quartz itself. It is wise to limit crystal current to a maxiumum
> of 40 mA

I think 60 mA is the absolute maximum. After that, bad things CAN 
happen.

> with any crystal in any circuit and there are tried and true
> methods for doing that if you are concerned.  One of these is a small
> pilot light bulb in series with the crystal.

The pilot bulb should be in the circuit only for testing, since the heating 
and cooling of the filament as the rig is keyed can accentuate chirp.

In the circuits I have seen, a 2 Volt 60 mA bulb is recommended.

I might add that I have posted an article from an RCA Ham Tips to the 
Glowbugs website detailing a single-tube 813 crystal oscillator 
transmitter. Power output is 150 watts CW, and 100 watts AM phone.

Power input is 300 watts on CW.

Total current through the crystal is 14.2 mA on CW, and 10 mA on 
phone. The 60 mA pilot bulb mentioned above is used in this circuit 
also.

Jack Meadows, W7QQQ, uses his version of this rig to drive an SB-200 
amp, and the combo sounds very nice on the air. No chirp, clicks or 
drift.

The info on this circuit is posted to:

http://www.mines.uidaho.edu/~glowbugs/

Click on 2) Transmitter Circuits, then 6) 813 Crystal Oscillator.

Ken Gordon W7EKB

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