mercoledì 12 novembre 2014

Rocky Tube QRP tx

Got from several circuit and then modified as I did not have components needed.
This is a first attempt to make a simple XTAL rocky TX with low power. Using some xtals on 40 m, and thinking to modify the frequency pulling of the xtals in future as suggests F6HCC in his nice webpage.
The original circuit was taken by an ECL82 single valve QRP TX from  G0UPL & c., but by the way I broke the valve (first time in 40 Ham carrer...:-( ) and so I had to modify as I have not yet any ECL82 for spare (Murphy law alway valid!).
A really good suggestion and link came from my friend Enrico IW3FZQ

So the choice has been for a 6N7 double triode as I have three of this: first is a XTAL Pierce oscillator and the second triode stage is a driver and the PA is made by a 6L6 old fashion tube (what I used on my Geloso VFO G4 102 in 1974 at the beginning).
The schematic are quite all the same and seems a really simpleto put together the component and in a couple of hours to be on the air.
Not for me!
First of all I don't have a lot of components in my actual lab, as when I moved from old house in Rome I left a lot of them in the boxes in a wharehouse and they are there yet. So I had to carefully choose also resistors I had from an old Oscilloscope I dismounted and also the tube socket was a spare without one pin and so on...
Then all was assembled and oscillator and driver were ok but no so strong signal. I mounted the 6L6 amplifier and so discovered that power was just less than one Watt!

Checked all voltages and circuit no reason to have so QRPpp signal, but after dinner I had an idea to make the signal growing with a resonant LC tank. In fact I remembered a simple "75watter" article on some handbook and between the 12BY7 oscillator and PA was inserted a simple parallel LC circuit.
I made it and connected and magically the power raised a little bit less 5 W!

 The Bird says about 5 W!


The complete TX now :-)....  no cosmetic 
(in the middle the new tuning capacitor for the driver stage)

So now the TX is functioning althoug is really just a prototype, but it's ok and it's mine and is nice to view in the dark evening with the two tubes lightning and the hot from them and from the dummy load (just a couple of paralleled 100 Ohm 2 W resistor).


Power supply

Tomorrow I'll do the key circuit on the cathodes and I'll make a try for at least one QSO, but this evening I'll go happy to bed for this my first valve TX in the new Ham era for I5SKK.....hi

The new LC tuning for drive

2nd harmonic at 14 MHz is 32 dB down

Yes, the home construction is really a doping for Hams...hi

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