ERF7530 equivalent replacement?

I have a specialized transistor tester that can tell you everything you want to know about a given transistor. I need one transistor that is not blown. I do not have one nor can I find one locally.

 

Biggest parameters to watch are gate charge, input capacitance, and turn-off time.

Every power MOSFET will have a max frequency at which the gain falls to unity.

That is, the power out will equal the power input.

The 7530 seems to have roughly a four-to-one power gain, so that "unity gain" frequency is above 27 MHz.

And a great many of the high-power MOSFETs will have an upper frequency limit of a few MHz or maybe ten. Not so useful at 27.

And that's the tricky part. The published specs don't reveal this directly.

But it's related to "Gate charge", "Fall time", or turnoff time and "Miller capacitance".

Still haven't learned how to translate the specs they give you for a MOSFET they sell to use as an on/off switch to specs that will predict RF performance.

And if you have a gadget that measures gate charge and Miller capacitance, that would be cool.

Just finding a 7530 that's not blown out would permit measurement of the gate capacitance. Shouldn't be too tricky to set up that one with a normal capacitance meter.

Would give you a number you can compare to the published specs for a possible substitute.

Pretty sure Eric won't be telling us what the original type number was for that part any time soon.

73

 

I have just the proper tool for test FETs. It will tell all of that and even if it is an enhanced mode FET. They use those primarily in switching applications. If you have a fet with just a little too much gate capacitance there are ways to fix that. Sorry can't get the formula to appear properly

NKA
C= -------
D
N is the number of plates
K is the dielectric constant
A is the area of the plates
______________________
D is the distance
between the plates
This is the simplified capacitance formula.

 

I'll have to look, I organized recently so I'd have to figure out which bins they are in. I have several.

 

I hope it's that easy. Then again if it was I'm sure there would be several of these tools out there and the replacement final would already have been identified. You just can't find these any where.

 

They are out there if you want to put the money into a piece of test gear you won't use very much. They are primarily "Arduino" based hand held devices and not very expensive compared to the SENCORE units I have.

 

The ERF7530 as used in the RFX-75 add-on amplifier would show between 75 and 100 Watts PEP.

The size of the heat sink made a carrier power much over 15 Watts a bad idea.

Considering that the manufacturer called their two-transistor version the '150' leads me to suspect that 75 Watts apiece was what they felt confident claiming.

I suspect that the difference in power from the RFX75 had more to do with variations in the type of radio it was used on.

The RFX75 has a ERF2030 (disguised IRF520) inside, driving the ERF7530. Not sure just what power the 2030 pumped into the 7530, but I'll guess it was around one-fourth the module's peak output power.

Probably ought to take a derelict RFX75 and configure it to test possible substitute parts.

TIme to order some IRFP240 and 250 parts to try that way. Comparing the specs of the two is a bit confusing. Gotta learn how to apply "gate charge" and "rise time" to RF-power gain.

73

 

You need to watch the impedance on RF75,150,300 etc.......If you look closely at it they are not 50ohm which makes the output power suspect. Same thing goes for the RM Stinger board when you cut that big resistors legs to get the power from 50 watts nominal up to 100-150 watts the impedance match goes out the window. No one seems to bother to check impedance on these they just assume it must be 50 ohms.

When people just take an existing circuit design and sub in fet's it is almost never right. You can not treat a mosfet like a bjt in the circuit. the Mosfet's should not even work but they do but almost everyone forgets that we use 50ohm for coax and antenna impedance.

Not only that but at 12V and 27Mhz the gain is almost nothing for these fets and when looking at "am" only radio's and the 50-150hfe gain a lot them had on the driver and final you are losing a lot to gain some watts. In a Cobra 29/Uniden 76/78 a well-tuned stock radio can key all over a mosfet moded radio especially if the fet radio had hifi or broad audio!!!! The fet radio will be loud and proud locally but just will not talk as far as you would expect. When the audio and rf are not linear. It is even more apparent when driving an amp. And lastly, if your SWR is just slightly high poof goes the fet! I have keyed bjt's with less than ideal swr's for hours at a time and never had one fail on a T-hunt. Mosfet's you go over 1.5:1 and poof....LOL They are cheap.

I am sure some of you are aware of this but they do actually make RF specific mosfets that actually have at least as much gain on 27Mhz and the 2SC1969. SSB radio's used bjt's that made more power but they were always low gain compared the the drivers and finals used in "AM" only radio's.

The only reason to use a non-rf specific mosfet in a CB is because they ultra cheap and idiots that chase insignificant watts on a meter are impressed! Did I mention they are ultra cheap?????

I hate lies and subterfuge and it seems like no one on this site ever mentions cheap, low gain, low durability when talking about non-rf fet's it is always about insignificant watts. Worse thing you can do to a radio after super swing mod's is put a fet in the radio in place of a a bjt because you or your customer are too cheap to put the right part back in while we can still get the right part. It is not like we can not still get he right part they are just not dirt cheap. They are however not insanely expensive either. It is not as if you need to put 10 matched 2SC1969 in a radio.

 

people have said fet mods are shit when they first appeared in new rigs,
i would not entertain a rig with shitching fet finals,

removing bipolars & fitting shitching fets is on par with nitro knobs blue ch led's & chrome cases.

 

The most important difference between the ERF7530 and the IRFP250 is the input capacitance. The 7530 input capacitance runs between 2.18 nF and 2.10 nF not bad.
The IRFP250 input capacitance runs between 4.22 nF and 4.19 nF.
Interesting Note: They are both N channel ENHANCED MODE. The enhanced mode means that they both conduct a small amount "Magnetizing Current" without having to biased in the on condition.
Which also means the ERF7530 is a switching transistor.
The differences in input capacitance, the IRFP250 is almost double the ERF7530.
I don't think it matters very much at 10 meters and lower. A good circuit design can negate this small difference. We are dealing with nano Farads not micro Farads.
The 4.13 nF converted to uf is .00413 uF not too hard to compensate for.

 

This is an upgrade replacement ...... ERF9530 ..... I purchased 4 of these to replace the ERF7530's in a Palomar HD450 FET amplifier ......

https://www.rfparts.com/rftransistors/transistors-erf/erf9530.html

ERF9530 RF Power Mosfet Transistor, 100 Watts PEP, 30 MHz, TO3PN Case

The ERF9530 feature new silicon wafer designs with greatly improved quality and durability. Palomar’s new wafer technology creates a new level of ruggedness for these RF power MOSFETs that are now able to withstand all adverse conditions - high heat, high VSWR, high voltages and current levels.

The ERF9530 is a drop-in replacement and upgrade for the ERF7530 transistor and features a new TO-3PN insulated package for the mounting screw. The ERF9530 is conservatively rated at 100 watts PEP.

FEATURES
• High Power and Economical:
Pout > 25W (100W PEP)
Gp > 10dB @ 12.5V, f=30MHz

MFR: Palomar