ss modulator

[K5IIA]

I am helping a friend build up a single 6146 transmitter. he is building it for the experience and i am just along to help him.

af first i was going to recommend using a hammond audio transformer hooked up in reverse. then a solid state pa amp to drive that.

well what i would like to do now is build a modulator with the transmitter. series modulator is a term i have heard. pw modulator.

my question is this. for someone with zero experience in ss componets. well i did build a 20a regulated power supply with pass transistors that did work. but that is all i have done.

here is what i would like. for it to accept either hi-z d104 mic or low imp studio mic.  not sure if the modulators are sensitive to input impedance or if they work another way.

and then for it to just modulate the 6146. plate voltage will be 500v.

so if anyone has any input or a thread they can send me a link to that would be great.

i figure this will be a good warm up for my future project of a class e rig.

thanks for any help and maybe i can shoot out some more questions after i get an answer or two and figure out what direction i want to go in with this.

[Opcom]

Once you calculate the voltage ratio, you can pick a transformer but the impedances offered.
Picking one made for a single ended amp might avoid some of the saturation issues, or you can use  modulation choke if necessary.
500V should be OK.

[K5IIA]

http://amfone.net/Amforum/index.php?topic=27856.0

i was looking at this. and wanted to see if i could use that circuit or something similar.

i would like to get away with having 2 inputs, either d104 or rack gear.

and then not have to use a modulation transformer.

i know what i want for inputs and i know i want to modulate a single 6146. just dont konw what i need between them. 

that circuit in the link would need a preamp? i am guessing.

[Opcom]

Yes just a preamp, he says 20V p-p so it's a bit more than most cheap-o preamps make but a good op-amp with a +/-15V supply might help, or a small home stereo amp, of the type where it has one side grounded and only one speaker lead is hot, rated 8W ->8 Ohms or more (7.07V RMS) would provide enough voltage according to the article.

Apparently Bob it working well. Notice the various capacitors and diodes around the FETs and the 100 Ohm resistors in series with the sources. Be sure not to omit such things as they help protect the devices.

The series modulator dissipation total with a 1000V supply will be only 56W for a 6146 running 500v on the plate at carrier cond.

The 160 Watt STW4N150's he has used are a good choice but they need insulators. If you insulate the heatsink for the B+, you can just bolt them on with some compound and omit the insulators for better thermal transfer. The 63 Watt STFW4N150 has an isolated TO-3PF case requiring no insulator at the cost of the lower dissipation, it's the same die and a pair should be fine. There's a TO-220 version as well but I suggest the larger packages for the greater pin spacing. These transistors are rated 1500V/4A/150 deg C junction temp and  also have an internal protection diode.

One thing I noticed is that the input jack has no resistor to GND. It's not mandatory but I would put one there if using a preamp/amp that has a capacitor coupled output so the cap can charge/discharge properly.

Why not PM him and see if he has any advice from his experience so far.