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Paul Burridge wrote in message . ..
Okay, thanks all and keep it comin'. I had no idea there were power FETs capable of UHF. I'll follow any links given and investigate. Check out www.polyfet.com; SR706: 300 watts at 225MHz. SR705: 200 watts at 400MHz. LX401: 60W at 1000MHz. Also some very terse "ap notes" and some somewhat less terse but very to the point technical papers. |
On Wed, 05 May 2004 20:13:01 -0400, Ken Scharf
wrote: Mosfets in the MRF5xx series (511, 521 for example) have been used up to the 10 meter band with good results. A pair of them can give at least 50w pep output. Depending on the input/output circuitry used and the transistor they require 12-28v power supply. Layout is somewhat critical. THanks, very interesting. I wonder if anyone's tried paralleling up half a dozen of 'em for more power? -- The BBC: licenced at public expense to spread lies. |
On Wed, 05 May 2004 20:13:01 -0400, Ken Scharf
wrote: Mosfets in the MRF5xx series (511, 521 for example) have been used up to the 10 meter band with good results. A pair of them can give at least 50w pep output. Depending on the input/output circuitry used and the transistor they require 12-28v power supply. Layout is somewhat critical. THanks, very interesting. I wonder if anyone's tried paralleling up half a dozen of 'em for more power? -- The BBC: licenced at public expense to spread lies. |
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On Wed, 05 May 2004 20:21:45 -0400, Ken Scharf
wrote: BTW I have a bunch of 813's I'd be willing to sell. Someone make me a good offer on a lot of 5 of them. (Used, but don't look too bad). Nice. Got any KT88s? -- The BBC: licenced at public expense to spread lies. |
On Wed, 05 May 2004 20:21:45 -0400, Ken Scharf
wrote: BTW I have a bunch of 813's I'd be willing to sell. Someone make me a good offer on a lot of 5 of them. (Used, but don't look too bad). Nice. Got any KT88s? -- The BBC: licenced at public expense to spread lies. |
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On Thu, 6 May 2004 17:43:10 +0200, "Fred Bartoli"
r_AndThisToo wrote: "John Larkin" a écrit dans le message news: ... On 5 May 2004 16:41:11 -0700, (Tom Bruhns) wrote: Back when hexfets first came out (1981 or so), I was having trouble with them self-destructing. Back then, at least, if you read far enough in the fine print, you'd find a maximum drain dv/dt rating. And the substrate diode made a nice step-recovery diode, making it possible to generate lethal dv/dt's in totally non-obvious ways! If the drain load is resonated and you want some control over the resonant frequency (i.e. you have external to the mosfet tuning Cs) I don't see much discontinuities in inductors current. Of course when all the stuff is well "wired" and that's an entirely different matter, isn't it Paul ? ;-) John, can you suggest some refs that nicely snap ? I think that most mosfet substrate diodes are now designed to have soft recovery, so that they won't snap and make a horrible dv/dt. I blew up a lot of early Motorola mosfets in an h-bridge motor driver... had to switch to darlingtons, and only figured it out later. Anything with a p-i-n structure has a chance of being a snap diode. I think it needs a hyperbolic doping profile or something to work well. 1N4005-7 types work, but usually only after a brief forward bias, not DC. Somebody told me that many varicaps snap, but I haven't verified that. Specifically-designed PIN diodes (the kind used in RF switches and attenuators) don't snap, as they are doped to have very long recovery times. We tested over 60 different TO-220 power diodes to find the best high-voltage drift step-recovery part. Then we found something else, much better and more repeatable, but that's still a secret. John |
THanks, very interesting. I wonder if anyone's tried paralleling up
half a dozen of 'em for more power? ================================== Mind in-&output capacitances ,which add-on when parallelling. Frank GM0CSZ / KN6WH |
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