If the sound quality on the bipolar amplifier was poor, it sure was not due to the MRF455 transistors it used. More than likly it was being overdriven because those transistors, have much more gain than the switch mode MOSFET's and require less drive power.
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Rocketbox info thread !!! Made in the USA with a reasonable pricetag !
- Thread starter WINKDOGG
- Start date
I never said the sound quality was "poor" on the Motorola mrf455 transistors.
I said the Mosfet amp sounded "Much better" Both amps were used with the same direct injected audio system so they were not being overdriven & had plenty of head room.
Linear amplifiers do not alter the audio in any way, unless the amplifier is not running linear. The drive requirements for two MRF455's, is also going to be noticeably lower than any MOSFET likely to be used in the other two pill.
k8cpa
Certified Weirdo and old fogie
If I were the builder, I'd be really careful disclosing where I am. Too many eyes. Just my 2 cents.
F&&k Facebook! They block me for 30 days just about every 3 months. They love to censor my 1st amendment rights.
I fired FB years ago.
I just ordered a HD 250 MOS from his website. He had a sale going on this past weekend on those. I think I saw on FB that he is extending the sale for a few more days.
Thanks to WINKDOGG for the notice of his products. He responded fairly quickly to my questions about it before I pulled the trigger. Looking forward to trying it out.
Here is a link to his website.
rocketboxelectronics.com
Thanks to WINKDOGG for the notice of his products. He responded fairly quickly to my questions about it before I pulled the trigger. Looking forward to trying it out.
Here is a link to his website.
Rocketbox Electronics
Rocketbox amps for radio communication (cb radio) cb linear, palomar, 9530, rocketbox 250, rocketbox 500hd, and other electronics supplies
rocketboxelectronics.com
That looks real clean. Starting to be glad I ordered one already since you posted that picture. Hasn't come in yet but I'm looking forward to it even more. Nice.
Hey, at least he warns you to keep the SWR below 1.5 to 1.
Does suggest the MOSFETs being used are the low-frequency types adapted to RF like the 9530. They are not built to tolerate SWR and tend to go POOF! in the face of an impedance mismatch.
Does this mean he figured out the secret identity of the ERF9530?
Probably won't let on if he has.
73
Does suggest the MOSFETs being used are the low-frequency types adapted to RF like the 9530. They are not built to tolerate SWR and tend to go POOF! in the face of an impedance mismatch.
Does this mean he figured out the secret identity of the ERF9530?
Probably won't let on if he has.
73
They are on the expensive side for a stamped out surface mount board. Most amp builders start with a copper board and actually build an amp that is then hand tuned. I would rather pay for that kind of work. The mosfets they use are not even transmitting finals. When you read the specs they seem to require a lot of peak drive. I prefer a switched SSB delay. A local guy tried one years ago when they first came out, sounded a bit crunchy or harsh on SSB. I wish they were class AB with some filtering like the blue face Palomar/Cobra/Magnum amps had years ago. That said the best part about this hobby is anyone can try what ever amp or radio they want. At this point maybe some members here can test them out and hopefully have good results.
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While I haven't tried it at 12 volts, years ago I used the Mauser part locator - filter on their website to find decent MOSFET's for RF applications. It might work to find a replacement for the ERF-9530
The trick was using this filter to select package style, dissipation, VDD, and most important, the turn on and turn off times of the device. That determines the upper frequency limits.
To get those numbers I just looked at another well-known RF MOSFET, rated to 30 MHz. Then set the filter on the Mauser website to be equal to or less than those numbers . As long as the gate input capacitance is below 3,000 pf, it's still relatively simple to match it to 50 ohms at this frequency. The gate capacitance of an inexpensive switch mode transistor can be much higher than a quality linear rated RF transistor.
Just about all of the inexpensive transistors that will work to 30 MHz, will be rated for nonlinear operation with no bias. With gate turn on voltages of approximately 4 volts, running an unbiased amplifier with these types of transistors, doesn't even work well on AM. They require bias and as soon as you start adding it, the published dissipation ratings drop to about 25%.
I've seen parts used at much higher voltages, that were rated for 500 watts dissipation in class C or below, only safely handle about 125 watts in class B. Many fell apart in class AB, without accurate thermal tracking on the bias.
The problem is Class B still leaves some "crunchy" in the audio of sideband signals. The more bias you apply to correct this problem, the more unreliable the amplifier becomes, due to Thermal Runaway.
What I can say about amplifiers using these types of transistors, is you get what you pay for. They are relatively low quality and while that doesn't always show up in the sound of the signal, it is definitely in the reliability of the equipment. With that in mind, don't pay a lot for low quality. I think you'll get the same bang for less buck, out of something like an RM Italy.
I also wouldn't buy anything rated for more than about 250 watts PEP. Otherwise, you're going to have too many little transistors all trying to act in balance as one big one. Internal drivers on these amplifiers, can also be problematic. They rarely provide enough decoupling between the two stages, to keep them stable under all conditions.
The trick was using this filter to select package style, dissipation, VDD, and most important, the turn on and turn off times of the device. That determines the upper frequency limits.
To get those numbers I just looked at another well-known RF MOSFET, rated to 30 MHz. Then set the filter on the Mauser website to be equal to or less than those numbers . As long as the gate input capacitance is below 3,000 pf, it's still relatively simple to match it to 50 ohms at this frequency. The gate capacitance of an inexpensive switch mode transistor can be much higher than a quality linear rated RF transistor.
Just about all of the inexpensive transistors that will work to 30 MHz, will be rated for nonlinear operation with no bias. With gate turn on voltages of approximately 4 volts, running an unbiased amplifier with these types of transistors, doesn't even work well on AM. They require bias and as soon as you start adding it, the published dissipation ratings drop to about 25%.
I've seen parts used at much higher voltages, that were rated for 500 watts dissipation in class C or below, only safely handle about 125 watts in class B. Many fell apart in class AB, without accurate thermal tracking on the bias.
The problem is Class B still leaves some "crunchy" in the audio of sideband signals. The more bias you apply to correct this problem, the more unreliable the amplifier becomes, due to Thermal Runaway.
What I can say about amplifiers using these types of transistors, is you get what you pay for. They are relatively low quality and while that doesn't always show up in the sound of the signal, it is definitely in the reliability of the equipment. With that in mind, don't pay a lot for low quality. I think you'll get the same bang for less buck, out of something like an RM Italy.
I also wouldn't buy anything rated for more than about 250 watts PEP. Otherwise, you're going to have too many little transistors all trying to act in balance as one big one. Internal drivers on these amplifiers, can also be problematic. They rarely provide enough decoupling between the two stages, to keep them stable under all conditions.
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