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 Post subject: 6GY6 two tube transmitter revisited
PostPosted: Apr Thu 25, 2013 12:19 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 20347
Location: Warner Robins, GA
Figured it was about time to post an update about my 6GY6 two tube transmitter that started out as a kit provided by one of the fellow forum members.

I used it off and on when I built it, but for the last month or so its been on 24/7 and all I have to do is to turn on a radio and send the signal to the transmitter from my mixer and it just works every time.

I am more amazed/surprised that my DIY antenna tuner which was just thrown together with parts on hand without actually knowing what I was doing works so well. Tuning of the antenna tuner is accomplished by adjusting for maximum S meter indication on one of my communications receivers.

I had planned on adding a variable resistor in the cathode circuit of the 6GY6 so I could adjust for optimum signal strength and audio quality, but haven't done it as I really see no need as I get good signal strength and excellent audio quality.

I might use one of the ammeters I have and place it in the cathose circuit of the 6GY6 so that I can use it to properly tune the antenna tuner as IIRC at resonance there should be a drop in plate current, right?

I set the VU meter circuit to where it goes into the red right as I approach 100% modulation as seen on a scope.

Schematic

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Cabinet. Still have three switches installed that basiaclly do nothing which I need to remove.

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Antenna tuner. Oddly enough I had to add a small maybe 2-3 turn coil of wire between the coil and large variable cap in order for it to work right, but even a straight piece of wire worked. Not sure why though. Am assuming I formed a small inductor. I just use two bare wires to conenct the antenan tuner. Ine to the antenna terminal and one to ground. Is that ok or is there a better way.

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Antenna. Picture was taken when I had started experimenting with the antenna tuner.

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PS: Given this transmitter puts out a signal on harmonics nearly every 1 MHz I wound up using it in the alignment of one of my radios where I had to adjust a trimmer cap at the higher end of the band for dial tracking :P


Last edited by Tube Radio on Jul Fri 19, 2013 8:28 pm, edited 2 times in total.

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 Post subject: Re: 6GY6 two tube transmitter revisited
PostPosted: May Fri 10, 2013 1:49 pm 
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Posts: 20347
Location: Warner Robins, GA
Tried experimenting yesterday with adding a meter in the cathode circuit to measure cathode current to make antenna tuning easier and I got ok results, but couldn't find the box of five meters I bought so couldn't try different ones to see if another meter would work better. Figured out that if I wanted to use the meter's scale to measure current I'd need a meter with a scale that goes to either 10 or 15.


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 Post subject: Re: 6GY6 two tube transmitter revisited
PostPosted: May Fri 10, 2013 5:44 pm 
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With a shunt resistor you can calibrate a 50ua or so meter to give about any reading you'd like to see as normal...


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 Post subject: Re: 6GY6 two tube transmitter revisited
PostPosted: May Fri 10, 2013 6:31 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 20347
Location: Warner Robins, GA
I had used a 100uA meter in parallel with the 470 ohm cathode residtor and 30K of resistance in series with the meter. Tried the shunt method and for some reason didn't get any change in meter indication at all.

Need to find that box of meters I have and try them with the shunt method as that 100 uA meter might have not been sensitive enough.

I had been using the S meter reading on my R-390 to indicate when the antenna tuner is tuned properly which works, but a built in meter would be better.

At one point I thought of playing with the cathode resistor value, but after months of using it with the 470 ohm resistor and getting good range and audio quality I see no reason to change it.

I suspect if I used a wire antenna I could get better range, but would then need to build another antenna tuner. It must have good range as is given the transmitter is in a 12' X 12' building about 30 FT from the house (doublewide with metal roof and sding) and can be received pretty decently in my bedroom on a more modern tuner.

EDIT: Got the meter figured out. I found a meter in a defunct power supply that has a 0-50 volt scale so I would up using 6,290 ohms of resistance to make it read the correct cathode voltage. I plan on mounting it in the transmitter.


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