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307 Amps?

Why don't amp builders use thermal tracking for their biasing?
Simple thermal tracking can be applied by mounting the clamping diode to the top of one of the RF output transistors.
It's so very easy to implement a simple unregulated thermal tracking bias I don't know why anyone would build without it.
Of course if you are biasing up around the .7 volt range on your transistors (which is necessary for clean operation on SSB, that .35 volt on the base just don't cut it) you can't run unregulated 20 volt supply's!! I suppose that B bias stuff is for the guys that run higher voltage supplies. Of course I don't think any regulated bias designs would be very happy being "volted" either.
I don't mind the unregulated bias as long as it has the simple diode heat tracking trick, and applies .7 volts to the base of the transistors. The biggest problem with it is supply voltage has to fall no less than about 12 volts and no more than about 15 and the clamping diode has to be picked carefully so it doesn't supply to much voltage to your RF transistor base and blow them up. It needs to maintain no less than about .6 volts at 12 volts supplied to amp and no more than about .8 volts with around 15 volts supplied to amp.
This also will increase the gain factor of the transistors so less drive is required for the amp.
By the way I'm speaking from a Toshiba 2879 point of view. Numbers will vary with different RF output devices.
Bias those amps!
Panic Attack got down!
 
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I got a pic from the builder. I know the bias has a diode with 2 caps under those resistors someplace, but it's pretty hard to see in the pic.

Good, bad, or just another copy?

received_353093000330396.jpeg
 
Light duty build. No heat tracking applied to the bias circuit. Output combiner needs to be larger, if you want those big watts lol. Looks like it will work though....pretty typical B bias build.
 
I'd run it! It's a clean build and he used good caps, it looks like, for the tuned output sections.
 
Anyone know anything about 307 Amps? Jim Mcknabb in Gillette, WY?
Yes, don’t buy from him. He builds “great” boxes for his buddies and everyone else gets cheaply made ones. A buddy of mine is out over $2,000 because Jim put a cheaply made power supply in his box and it blew within using it a few times. He does this to have people keep going back to him to “fix” the issue. I highly do NOT recommend him. He builds cheap to keep you coming back for repairs.
 

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