[600MRG] 630 meter Homebrew

[Eric NO3M]

I recently built an amplifier that uses a similar lineup: 6AG7 -> 6V6 -> 
2x 807 (parallel).  1mW or less is plenty of drive.  It could be 
converted to a stand-alone rig by modifying the first driver stage as an 
ECO.

If going to parallel 807s (or 1625s), a 6AG7 oscillator (xtal or ECO) 
probably won't have enough output to fully excite the pair. Following 
the 6AG7 with a 6V6, 6F6, or 6L6 running Class A (untuned grid, tuned 
plate) will do the job as well as provide excellent buffering.  If using 
an ECO, the grid may have to be tuned to 1/2 freq. for best stability; 
at least that's the best configuration in my 89 -> 42 -> 802 exciter, 
even on 630M.

If you want to graduate to the next power level from 2x 807s and like 
the old beam tubes, try a pair of 814s.  Need more, a single or pair of 
813s.

It's nice to hear about some of the glowbugs floating around on 630M.

73 Eric NO3M


On 01/28/2018 04:37 PM, Dwight Blevins via 600MRG wrote:
> I see there's an ongoing discussion on a homebrew tube transmitter for 
> 630 meters. I just built one and it was a most rewarding experience. 
> It was a bit more difficult than I expected, but quite doable for the 
> average ham. Mine is a takeoff on one posted online by a ham in 
> Australia (VK1S?). He used a 6AG7 to drive an 807. I used a 1625 for 
> the final, much the same tube as the 6BG6, 807, 1625, 6l6, etc. It 
> produces about 20 watts output.
>
> Forget the ease of the old 6V6/6L6 style transmitters, which most all 
> of us have tried at some point in the hobby. The high value L/C 
> configurations of the MF/LF spectrum are something located in the 
> pages of another book that many of us have not yet read. Thankfully 
> the online schematic that I found got me in the ballpark, but I still 
> spent several days of cut and try, getting things to gel for my 
> particular setup. I learned some valuable lessons that I'll not soon 
> forget.
>
> If I had it to do over (and I probably will) I'd have gone for a dual, 
> parallel output in the final. This would produce around 35 to 40 watts 
> out, which, based on my experience thus far, I feel is minimal and 
> needful from a practical standpoint. Many of us do not have a very 
> efficient antenna, so I feel that if you don't have at least something 
> close to a minimum power in the 40 to 50 watt range, then you'll have 
> considerable difficulty making contacts with cw. The challenge might 
> be a little less for those living in areas of high population, but 
> there are just not yet that many hams operating 630m.
>

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