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MOSFET conversions for upD858 and MB8719 boards
- Thread starter ExitThirteen
- Start date
Thanks for sharing your expieriance and i can tell its all for real to because your willingness for providing all the details needed for the results you got and im gonna refer back to this post when i get my grant radio that i also want to do the mosfet upgrade as well
Squints,
to be clear, changing the original final to a MOSFET is not an upgrade.
the only reason to do this mod is if the original driver or final blows and you can't find a replacement.
your radio may do a few more watts with a MOSFET but it also may do a few less.
These types of mods are not written as a tutorial for the average home gamer to follow.
these mods are written for fellow technicians that understand that there may be circuit modifications necessary once the mod is done.
If you are not familiar with how to change the gate voltage based on quiescent current, or changing the values of parts in the driver and final sections then i would not recommend trying this.
Exit13 knows his stuff but there are too many variables for this to be some sort of "kit" that someone could buy on ebay and have repeatable results.
LC
to be clear, changing the original final to a MOSFET is not an upgrade.
the only reason to do this mod is if the original driver or final blows and you can't find a replacement.
your radio may do a few more watts with a MOSFET but it also may do a few less.
These types of mods are not written as a tutorial for the average home gamer to follow.
these mods are written for fellow technicians that understand that there may be circuit modifications necessary once the mod is done.
If you are not familiar with how to change the gate voltage based on quiescent current, or changing the values of parts in the driver and final sections then i would not recommend trying this.
Exit13 knows his stuff but there are too many variables for this to be some sort of "kit" that someone could buy on ebay and have repeatable results.
LC
In the world of computer programming, there's a cliche about bugs in the program. If a bug looks like too much trouble or expense to fix, they say you should "dress it up in a tuxedo and call it a "feature".
About the whole idea of MOSFET technology. This kind of transistor is replacing the older Bipolar Junction Transistors like the CB finals and Toshiba linear transistors we have become used to since they quit using tubes in the 1970s. Time marches on, technology evolves.
If it weren't for the european ban on lead in electronic solder, those parts probably would never have been discontinued. But they were. All of them. Only a few of them were re-tooled as lead-free versions, like the low-power stock final in AM-only radios like a Cobra 29. Any parts made with those numbers now are coming from a third party in China, not from Toshiba or Mitsubishi. The quality level of the original Japan parts was higher than you'll get from China.
Manufacturers had to come up with a lead-free solution. There are MOSFET transistors designed to be rugged RF power amplifiers like the old 2SC1969. Trouble is they cost a few bucks, even in large quantities. The MOSFET transistors they changed over to use are NOT designed for RF. The IRF520, FQP13N10, ERF-2030 were all designed to use as on/off switches. As in, switching DC power on and off 50,000 or so times a second. This is the basis for every "switchmode" power supply. They're found in every AC power supply from the wall wart that charges your phone, inside your overclocked gaming box, light fixtures, etc, etc. The insane production quantity makes them cheap, under a buck. These switchmode transistors will amplify RF power even though they aren't built to do that. But efficiency will be low. This will boost the power supply current you need to produce the same RF power as before.
Any kind of component made in those quantities becomes incredibly cheap. In this case, under a buck, compared to several bucks for a legitimate RF-designed MOSFET.
The RF MOSFET contains protection from high SWR.
The switchmode transistor does not. The MOSFET transistors that are hawked as an "upgrade" are the cheap version, and will pop any time the SWR is at all high for any length of time.
This saves the factory a bundle. And costs the end user when a modest SWR pops his final transistors.
So yeah, smear lipstick on it and call it an "upgrade".
I think I hear my snake squeaking. Time to buy some more oil for it.
73
About the whole idea of MOSFET technology. This kind of transistor is replacing the older Bipolar Junction Transistors like the CB finals and Toshiba linear transistors we have become used to since they quit using tubes in the 1970s. Time marches on, technology evolves.
If it weren't for the european ban on lead in electronic solder, those parts probably would never have been discontinued. But they were. All of them. Only a few of them were re-tooled as lead-free versions, like the low-power stock final in AM-only radios like a Cobra 29. Any parts made with those numbers now are coming from a third party in China, not from Toshiba or Mitsubishi. The quality level of the original Japan parts was higher than you'll get from China.
Manufacturers had to come up with a lead-free solution. There are MOSFET transistors designed to be rugged RF power amplifiers like the old 2SC1969. Trouble is they cost a few bucks, even in large quantities. The MOSFET transistors they changed over to use are NOT designed for RF. The IRF520, FQP13N10, ERF-2030 were all designed to use as on/off switches. As in, switching DC power on and off 50,000 or so times a second. This is the basis for every "switchmode" power supply. They're found in every AC power supply from the wall wart that charges your phone, inside your overclocked gaming box, light fixtures, etc, etc. The insane production quantity makes them cheap, under a buck. These switchmode transistors will amplify RF power even though they aren't built to do that. But efficiency will be low. This will boost the power supply current you need to produce the same RF power as before.
Any kind of component made in those quantities becomes incredibly cheap. In this case, under a buck, compared to several bucks for a legitimate RF-designed MOSFET.
The RF MOSFET contains protection from high SWR.
The switchmode transistor does not. The MOSFET transistors that are hawked as an "upgrade" are the cheap version, and will pop any time the SWR is at all high for any length of time.
This saves the factory a bundle. And costs the end user when a modest SWR pops his final transistors.
So yeah, smear lipstick on it and call it an "upgrade".
I think I hear my snake squeaking. Time to buy some more oil for it.
73
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I'd like to thank all those who contributed useful information on how to "Get 'er done", for those old CB's that can enjoy a second life after their 2SC1969's failed.
It may simply be a matter of semantics but I'd say going from a defective CB to a functional one counts as an upgrade.
Yes, I have seen power output improvements but those are merely a by-product born of necessity.
I would never advise anyone to yank their 1969's for a shiny new IRF520.
I would be glad to fit some to get your favourite old rig up and running again.
Enough said.
73 to you all!
It may simply be a matter of semantics but I'd say going from a defective CB to a functional one counts as an upgrade.
Yes, I have seen power output improvements but those are merely a by-product born of necessity.
I would never advise anyone to yank their 1969's for a shiny new IRF520.
I would be glad to fit some to get your favourite old rig up and running again.
Enough said.
73 to you all!
- No one is chatting at the moment.
