oh i also have a motorola cquam and REA am mono modulation monitors, old eico sig genny, frequency counter and l/c meter as well for my test gear.
test gear and parts wise i'm good. already have the psu from computer to scrap for toroids need to find mosfets and some of the other parts. wish i had kept that old car amplifier now i would have had the mosfets.
Well with carrier current be darn careful of those live wires. Don't want to know someone fried themselves here.
Do you have any tube gear available for scrapping? A pair of 6V6s may get the job done. That or buy a used ham amplifier on ebay and rip it apart and use what you can to build a new amp.
Converting an old amplifier is not easy. The closest thing that could even work for mediumwave is a used 160 meter band amplifier which is not found easily.
Getting past the 5 or 10 watt level is where the challenges begin for hobbyist. Then add in the fact that it's AM and you need 4 times the headroom making that number jump to 20 to 40 watts for a proper linear amp!
if i drove this design with 80-100mW CQuAM from a sig generator (not sure if that is peak or rms) what would the output be of this design?
i am very well aware of A/C current. been playing with electronics and electricity since 5 years old.
Not sure exactly since there are too many factors that come into play. One of those being that I don't even know the exact toroid type I used, they were just scrapped from a computer power supply and are god knows what mix, but any medium frequency toroids should work with experimenting on the coiling lengths.
I suppose if you use properly designed transformer stages with very low loss you could get 10 watts carrier out with as little as 100mw carrier input (with higher VCC voltage as I talk about below). I know I was able to achieve near that amplification but it took me some time fiddling with how many coil windings worked best for the toroids I had to work with.
When I get some coffee in me in the near future I can reply with some more technical based information. With mosfets you have to look at how much gate voltage they can handle, not go past that level but drive it near that point (only at full modulated input). That way you can achieve higher gate efficiency. Also the output stage transformer should be made for maximum power transfer. Driving the gate with much less power than it's capable of means getting lower efficiency, thus forcing you to crank up the drain input voltage to get the same wattage output. Of course there is a limit to that before breakdown of the mosfet. With as little as 100 milliwatts (400mw 100% modulated) divided by 2 (for push pull operation) you get 200 mw at the input of each gate. That equals to around 3 volts, probably less after the input transformer. Obviously that is much less than the average gate on most power mosfets can handle, so that means you will have to be driving the linear amplifier with much more VCC voltage to get close to 10 watts output. Just be careful not to push it too close to the limits of the parts. Obviously you could just run the amplifier with the safe voltages I mentioned in the schematic with less power output.
I found that with my amplifier I could probably get much more than even 40 watts PEP if I drove their VCC harder and had much better cooling but I rather not find out where their snapping point is being as mosfets don't really appreciate linear operation in the first place ;D
Just finished building the 35w that you reposted. Why did you used N-channel MosFets? So far with my build it is producing a carrier but also it's own IF and it is overloading the source rig. Had to insert a diode in the LV power supply. After winding the Xforms I think I'll try P-Channels. I have 23uH for T1-T4, 97uH for the RFC's and 1447uH for T5 sound close to you?
Just finished building the 35w that you reposted. Why did you used N-channel MosFets? So far with my build it is producing a carrier but also it's own IF and it is overloading the source rig. Had to insert a diode in the LV power supply. After winding the Xforms I think I'll try P-Channels. I have 23uH for T1-T4, 97uH for the RFC's and 1447uH for T5 sound close to you?
As far as the front end loading goes, you may need to change the values of the first two resistors on the RF input. I designed this to match a transmitter I made ages ago so the input is not seen exactly as 50ohms. A simple way around this would be to just change the 250ohm resistor to 50ohm, and the 220ohm to whatever is needed to fully drive the mosfets with RF voltage without clipping the gates on full modulation. An oscilloscope would be needed to assure this. I used the FQP50N06 mosfets because that was what I had laying around and they worked equally as good as IRF510s that are commonly used for this type of design. I can't tell you much on your transformers but a web search for similar amplifier designs will get you in the ballpark.