i like genuine mrf454's, 20a & 250w pdis,
they make more power & hold together better than the 455, 1446 or 2290 in the right circuit.
they make more power & hold together better than the 455, 1446 or 2290 in the right circuit.
i like genuine mrf454's, 20a & 250w pdis,
they make more power & hold together better than the 455, 1446 or 2290 in the right circuit.
Considering there is almost no demand for this part as compared to the 2879 and the package shape of the Mitsubishi part is different than all others, it would not likely be a easy part to counterfeit. Yes, the MRF-454 is still sold by MaCom.I'd be interested in playing around with them. However, looks like all the 2SC3240's on eBay are from China, so they will all be fakes, if lucky maybe some are just used pulls that still have a little life left in them. But I'd be leery of ANY shipped from China.
Question, did MA/COM stop making the MRF454? Just curious, thought you may know.
I just realized that the MRF454 has a collector - emitter breakdown voltage of 25 volts! With 7 more volts of "headroom" than the 2SC2879, no wonder the MRF454 is so rugged. Even the dissipation is the same 250 watts that the 2SC2879 has. The only weak link with the MRF454 is the 20 amp collector current, being 5 amps less. Therein lies the key to your statement regarding "in the right circuit".i like genuine mrf454's, 20a & 250w pdis,
they make more power & hold together better than the 455, 1446 or 2290 in the right circuit.
I just realized that the MRF454 has a collector - emitter breakdown voltage of 25 volts! With 7 more volts of "headroom" than the 2SC2879, no wonder the MRF454 is so rugged. Even the dissipation is the same 250 watts that the 2SC2879 has. The only weak link with the MRF454 is the 20 amp collector current, being 5 amps less. Therein lies the key to your statement regarding "in the right circuit".
Isn't it ironic how the best RF transistor you could buy 35 years ago, is also the best one to still survive and be in production today? In the mid 1980's, most of the biggest HF solid state amps were using the MRF454. Several years later when the Toshiba hit the market, it really didn't take too much work to get those old circuits to match up with the new part.
Therefore, it would be very easy to go back one step and rework 2SC2879 amplifiers, to increase their input and output impedances to once again, match the MRF454. This makes me wonder if there is not a market to replace the 4 junk, TO-220 transistors we see in high power exports, with a matched pair of MRF454's? I can't imagine it would be too hard to fit them on the board, rewrap the input and output transformers and then scrub off 75% of the bias voltage with a 4:1 resistor divider...
It seems like this 2SC3240 transistor is very popular with Japanese CB'ers. I found several videos on Youtube showing everything from 8 transistors doing 2.6 kw, all the way to a 48 transistor amplifier. Most of them had horrible RF layout with like 8 feet of unshielded, non Teflon wire feeding the combiners.
The link below was the best build quality out of the ones I viewed. We can see he is using 3 wraps on the input transformers with a 1000pf cap across the base secondary winding. Also notice the output caps are one on each transistor, that go from the collectors to ground rather than across the collector primary winding. Now for the bad news, all of the discussion he provides is in Japanese.
Perkin Elmer had a similar issue with the RF exciter deck used in a Gas Chromatograph Mass Spectrometer. This RF generator used an MRF422 to drive an 8877. The MRF422 shares the common 211-11 package as the 2SC2879 but has a total dissipation of 290 watts! Under sustained carrier in class AB, they would distort the mounting flange no matter how robust the heatsink was.Watching him drawing he seems to be talking about how the transistors are screwed to the heatsink & the problem with heat causing the tabs to bow so the tab loses contact with the heatsink, common to see in our amps that are run flat out on FM,
its not just bowing that occurs, the the round part of the tab goes concave,
I have sanded dozens of bent & convex tabs flat using grades of wet & dry paper on a sheet of plate glass,