Since I am just getting started with amplifier repair I don't have much on hand in terms of replacement parts yet. Can anyone provide guidance or suggest some reading materials for selecting temporary MOSFET substitutes for testing purposes?
My question is more focused on FETs in the power supply section since finding substitutes for outputs is a crap-shoot and I'm not nearly experienced enough for that.
For example: I have a RF P300-1 with blown HUF75344G3's. I don't have any of those but would like to test the output section and order all the parts I need (plus extra) at once.
The N channel FETs I do have on hand are IRF3205PBF and IRFZ44NPBF. Are either of these an adequate choice for testing and what specifications should I be looking at to make an informed decision?
Thanks!
My question is more focused on FETs in the power supply section since finding substitutes for outputs is a crap-shoot and I'm not nearly experienced enough for that.
For example: I have a RF P300-1 with blown HUF75344G3's. I don't have any of those but would like to test the output section and order all the parts I need (plus extra) at once.
The N channel FETs I do have on hand are IRF3205PBF and IRFZ44NPBF. Are either of these an adequate choice for testing and what specifications should I be looking at to make an informed decision?
Thanks!
The IRFP064 is generally used as a sub for the originals in the PS. The IRF3205s have nearly the exact same specs (although that's not important for basic testing).
For testing at a basic level, you can use virtually anything. When output FETs fail, you generally have only one or two fail. The rest can't be reused (most reputable techs won't use used electronic parts in a for-profit repair) so you might end up throwing out hundreds of usable FETs a year. I keep them (bound together with a loop of wire) for testing. The outputs in the power supply won't be good for full power testing of the amp but they will certainly allow testing.
For testing at a basic level, you can use virtually anything. When output FETs fail, you generally have only one or two fail. The rest can't be reused (most reputable techs won't use used electronic parts in a for-profit repair) so you might end up throwing out hundreds of usable FETs a year. I keep them (bound together with a loop of wire) for testing. The outputs in the power supply won't be good for full power testing of the amp but they will certainly allow testing.
Thanks Perry, that is very helpful.
I have only been using new parts in the few I've done as I intend to sell the amps and prefer to do things the correct way. It doesn't make sense to use used parts when new parts are available. I like your idea of stringing used parts on a wire, that'll help keep them organized and not mix in with my new parts.
I saw IRFP064's with 47 ohm gate resistors were a common replacement. Other than costing about $1 less each, is there an advantage to using them over the original part?
Last question (I hope)
How critical is the gate resistor value for my low-power testing? The original parts are unreadable, I've read they should be around 60 ohm. Truth be told, I don't quite understand the importance of their value only that you use specific values with different FETs.
I have only been using new parts in the few I've done as I intend to sell the amps and prefer to do things the correct way. It doesn't make sense to use used parts when new parts are available. I like your idea of stringing used parts on a wire, that'll help keep them organized and not mix in with my new parts.
I saw IRFP064's with 47 ohm gate resistors were a common replacement. Other than costing about $1 less each, is there an advantage to using them over the original part?
Last question (I hope)
How critical is the gate resistor value for my low-power testing? The original parts are unreadable, I've read they should be around 60 ohm. Truth be told, I don't quite understand the importance of their value only that you use specific values with different FETs.
In most amps that have absolutely minimal deadtime, the 47 ohm gate resistors with the 064 is marginal. They sometimes have to be used with something like a 33 ohm.
Rockford uses the 60.4 in many of their amps. If you find that the 064s run hot at idle, go as low as you need to go to allow them to run cool.
With gate resistors, you have to find a compromise value. If you go too low, you stress the drivers. If you go too high, you don't control the FETs well enough.
Rockford uses the 60.4 in many of their amps. If you find that the 064s run hot at idle, go as low as you need to go to allow them to run cool.
With gate resistors, you have to find a compromise value. If you go too low, you stress the drivers. If you go too high, you don't control the FETs well enough.
Thank you Perry, that was a very easy to understand explanation.
I think, for now, I'll leave substitutions alone and stick with original parts for my final repairs. Perhaps I'll try some experimenting over the summer when I have adequate time to dedicate to it. I want to be confident in my repairs, my current level of knowledge and experience precludes that possibility if I were to use substitutions.
Thanks again! 🙂
I think, for now, I'll leave substitutions alone and stick with original parts for my final repairs. Perhaps I'll try some experimenting over the summer when I have adequate time to dedicate to it. I want to be confident in my repairs, my current level of knowledge and experience precludes that possibility if I were to use substitutions.
Thanks again! 🙂