[600MRG] 20 watts out with a 1625, low plate voltage?

[Bill Cromwell]

Hi Ike,

In addition to feedback issues that have been mentioned the plate supply 
for your final could stand to be jacked up a little. I have a Johnson 
transmitter with a single 6146 here with 600 volts on the plate (by 
design) and I get about 30 to 35 watts of output. Your TX power supply 
gives even lower voltage (under load) so expect somewhat less power out.

Higher output (100+ watts) comes out of three other radios with 850 to 
900 volts on the plates. One of those with no load is showing about 950 
volts! You might try for more than 20 watts output but I don't think it 
will be substantially more without a bigger power supply. You have to 
double your power for a little less than one S-unit at the distant 
receiver. That can make the difference between QSL and nada.

Good luck with your project.

73,

Bill  KU8H

On 01/28/2018 08:59 PM, Dwight Blevins via 600MRG wrote:
> I think my problem is with loading. It dramatically affects the plate
> current. I have a big antenna loading coil, probably 200uh, just outside
> the shack window. Multiple taps, easily changed, but the best I can do
> is about 70 ma at about 510 volts under load. The tap point also shows
> max signal strength when the same antenna is used for receiving.
>
> Maybe I'm getting a bit over 20 watts out, but not much. It will light a
> 75 watt light bulb at a nice orange glow, maybe 1/3 brilliance. Moving
> the coil tap very much causes a max load dip to about 50 ma, which is
> really deep, seeing off resonance the tube draws probably 125 ma. Just a
> turn or two in the other direction on the loading coil and the plate
> will not dip/load at all. The schematic I used called for all fixed caps
> on the Pi network. Boy am I ever glad I decided to at least use a
> variable plate cap on the Pi input. Fixed caps are just too ballpark.
> Next time I'm going to also incorporate a variable cap on the 6AG7
> output. Right now I have a 470uh inductor paralleled with about 250pf
> fixed cap. That gets it close, but a variable  would be better for
> peaking things up to max drive.
>
> Other problem is I'm using the old FT-241 crystals. Out of 8 crystals I
> found only two that are half way usable. The output changes
> dramatically, depending on the crystal. Probably be better off with a
> 7.6 mhz crystal and a divide down chip. Oh, forgot to mention, I have
> more inductance at the far end of the inverted L. It is a 160m trap,
> about 200uh, paralleled with a small coax make shift cap, to resonate at
> or just below 160m. This kicks up the radiation resistance a bit for
> 630m, rather than trying to have all the loading coil inductance near
> the feed point at the operating shack. All old school stuff for most,
> and maybe a boring read for some, but at age 71 I'm still learning :)
>
> 73, Ike
> KW7T
>


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bark less - wag more