Which Is Best For A Cobra IRF520 Or ERF2030 For The 40 Watt Mod

[9C1Driver]

Why not just get a linear and use that? It'll be far more stable, you're not over-working the radio past what it was designed to do, you've no worries about putting out crap, you've no worries about heat dissipation which I see everyone has failed to address, and you can get much more gain. Going from 20W to 40W is as pointless as going from 4W to 8W, it gets you half to a single S point.

Very good point. People have a false idea about a mosfet mod or conversion. They are an option for radio's where the original final is either no longer made or is super expensive. Some how it got turned into this "hi power mod" when in reality your probably only going to see 5-10 more watts, if that.
I had a test radio sent to me from Sparky's CB Shack many years ago, it had a mosfet mod, receive mod, and some kind of kick kit mod done. It was a great sounding and receiving radio that was well done. It was claimed to be a 40 watt radio, into an antenna with a Bird 43p it did 28 watts. I had a different radio done by a local tech that had a 1969 final mod done. It too did 28 watts on the Bird 43p.
I would rather have a clean peak tune and alignment done on say a Cobra 25/29 and then run that into a small amplifier if more horsepower is needed. If your a driver who cannot run an amplifier then maybe an RFX-85 mod done on the back of the radio would give you a decent increase in power. (if those RFX units are even still around).

 

[Tallman]

Very good point. People have a false idea about a mosfet mod or conversion. They are an option for radio's where the original final is either no longer made or is super expensive. Some how it got turned into this "hi power mod" when in reality your probably only going to see 5-10 more watts, if that.

Well said! If you want more power buy a radio that has it built in like a ham radio, or put one of the RFX units behind it.

 

[TheRealPorkchop]

Well said! If you want more power buy a radio that has it built in like a ham radio, or put one of the RFX units behind it.

Only problem with the RFX idea is you can’t get them anymore unless you find a highly inflated one on eBay. The PCN60 is a pretty fair option if you want something internal and hidden, cause you know, muh stealth.

The AD203 is another option but you have to lose the internal speaker.

Just stick an amp behind it and if that’s not an option then buy a radio that puts out the power you need/want - that’s my opinion.

 

[Tallman]

Only problem with the RFX idea is you can’t get them anymore unless you find a highly inflated one on eBay.
The AD203 is another option but you have to lose the internal speaker.
.

Thanks for the tip I have a freakin' gold mine in my stock room! RFX75's,80's, and 150's.
AD-203's a plenty too.

 

[TheRealPorkchop]

Well they been selling for outrageous prices on eBay. If you decide to sell some, start with the Dark Lord first...

 

[Tallman]

Must have real genuine wampum not that Darkside Spit coin. Yoda gets real pissed if he sees any spit coin in the till.

 

[686 Ghostrider]

I have used both the irf520 and the 13n10. The 520 didn't produce the power the 13n10 did but it was a cleaner power. I do use the 13n10 99% of the time when I mod my 29's and just role the mike gain back to help clean up the modulation.

 

[Handy Andy]

Actually, the MOS upgrade is almost a necessity.

The 2078 is not like it used to be and even as the years pass, it's not being used as often anymore.

Instead the Big 3 (Galaxy, Cobra and Uniden) they used the atypical 520 - only they "sand it off" so you don't know what is under the hood.

Below is a pic of the 687 those 6-pin Unidens that they say are their replacements to the PC-6X series...

Pay attention to the "chip resistor" markings...they provide you a clue...


Hint: 8.2K to as low as 6.8K and firmly paired with and use 4.7K in a voltage divider configuration.

Hope this helps

(EDIT - To Add)
The 2078 is a Bipolar. To still use it shows the "Backward" compatibility of some of these MOS upgrades. The problem lies in the support parts you'll need to help the swap work.

So if you're looking for 40-watts, DONT! I mean that, DO NOT try for that - better to use the MOS upgrade to develop a better punch and signal to audio envelope ratio of what many call 4:1 that being a fully modulated RF signal is 4 times the original carrier power - but that's if you trust your meter to be a PEP-reading-worthy meter.

If you get 4 watts carrier and it swings to 12~16 watts on a typical SWR/Power Combo Meter - you're fine.

If you go too extreme you can wind up doing more damage than it's worth.

Here's some examples...



They (read CB'ers wanting to make the conversion from Bipolar to MOSFET using the AN2030 methods) used to make their own self-powering Bias - which in light of the audio power presence - the self-powered ones make better sense than to use a simple voltage divider.

Here's what I guide myself with in MOSFET...


Why, well a voltage divider circuit is power flowing ACROSS your RF signal to your Gate (on MOS) or Base (on the 2078) ... Note the schematical references above. Bipolars can "self bias" (See R56 22 ohm Ferrite Bead and R53 1 ohm...)

The "self bias" method works due to the Bipolar and it's structure - it has a DIODE (well kinda - work with me here its a semiconductor) with DIRECT access across the BASE to Emitter/Collector - hence the Diode - and that means it can rectify RF. Yes, rectify - even if it's power level is TOO LOW to pass the built-in "voltage Drop" the Bi-polar exhibits - so RF can rectify to DC and once the Base conducts - power flows across the Collector/Base/Emitter can then provide the power needed to "Stay on" - the resistors provide the mechanism to stop this flow of power once the RF power stops flowing into the circuit (when you unkey to RX).

But MOS needs a little help, so you can "self bias" using a few extra parts - Zener or not, a diode is needed - ZENER would provide a "crowbar" to help keep the 520/13N10/2030 working because it would keep Gate bias low but cannot prevent excessive power from blowing up the gate and perforating your work into a dead short or popped part...

Hope this graphic helps show what I'm talking about here...


The Voltage Divider method is used in these cases.

In the old days Bipolar (2078) uses the Base as part of a Diode Junction NPN=the P=the Base and as trickle voltage can keep the transistor in the on state (Class C onto AB2) - The MOS isn't set up the same way - you need a P-N junction to form the rectification and a means to keep power flowing because the "Gate" is insulated (read very high resistor value) to the Drain and Source.

@loosecannon - a Cobra 19 Graphic that may help...


So hope the above hints helps - just don't overdo it and destroy your work. The IRF520 works - ok - as a Drop-in. But thre 13N10 have a power curve to offset it's limitations and couple nicely with the output networks used in todays radios.

 

[Handy Andy]

To finish this up...

Some Radios' provide you a means to apply this mod in a fashion that allows you to keep it simple yet also allow for some "distance" between you and the work the mod tries to perform. It keeps it cleaner and easier to swap or change parts to finish the install and make it work for the different MOS devices you can fit in there.

Ok, See Below...

It's from a PC-68/66 note the Ferrite Bead (L19) and R40 by the Final.


Keep the above in mind, the values shown in resistor values is Arbitrary, the Diode is oriented to supply a POSITIVE voltage (note the Band) - meaning I just put them together so you can see the ways you can use the fixed resistance and diode components to accomplish the "rectified feed" and the shunt needed to turn on or off the mess so it won't blow up on you.

Now if you are wise you can double check this by looking into a RFX75 or similar and ask ok, they used these values. Do I need to use them in this?

Yes, and No.

Yes, for the circuit design - so it can provide the power by "sampling" the RF power arriving into the Final from the Driver...

No? Because, the Values you see being used by them for sampling in the amps are for EXTERNAL install amps and are using the values needed BECAUSE THE AMP RECEIVES MORE OUTPUT POWER - so it does not need to "sample as much" to obtain enough power to turn on these parts. Now, if you had an SSB radio - it would be powered by SUPPLIED power to BIAS the part as an extra stage.

In this thread,
You are installing in an AM-only radio and if using the Self-Bias design. This can take more power from the Signal you're trying to amplify hence the cautions issued above to warn you about some inherited limitations from using a self-power bias scheme - you have to take something away to arrive at what is needed to power the Gate properly. Take too much power or waste it in this circuit to obtain a voltage or power level - you wind up destroying or degrading the signal too much and render this effort useless.

So since you're using small signal power feeds, best to use the Jumper shown above. Keeps your design away and "off to the side". However, to protect your work and the GATE of the MOSFET - install a simple low-ohmic value resistor INSTEAD OF THE JUMPER. Have this resistor take it's place. Value to use? Ok, say, 100 ohms to act as a buffer while you sort out the ideal values in the Triad (Resistor-Diode to Resistor-Shunt across) - you'll see power develop using different combinations but each time remember that you can "slam" the Gate with too much power or remove too much signal and arrive to "pinched sounding" results - step back and try again...

• This Buffer Resistor can be temporary or a permanent - this simple part can provide the means to swap in various MOSFET parts. I'm referring to the 13N10FQP response curve compared to a IRF520 - the 13's turn on quicker, but IRF520 provides more linearity. So the Buffer resistor is for the purpose of keeping your work simple yet effectively offering some method to interface and adjust your upgrade.

For those so-inclined, you can remove the Driver and sub in a 2166 and use a 33pF across it's Collector/Emitter to maximize the Miller effect. This swap will idealize the output of the Driver so you don't have to "sample so much of the signal" to obtain any result. Providing a larger power signal, your percentage of sampling requirements is less, which in turn, provides you less degradation of signal going to the Gate because you can use higher - more intrinsic in appearance to the RF signal, high-impedance sampling designs that will take less power from the signal to generate the Gates Turn on voltage as needed.

Good Luck!

 

[grimace]

how about a update did you get what you want out of the radio

 

[Shadetree Mechanic]

Wow Andy, have you ever thought about writing a book? Tons of good stuff here, I am going to print out Thanks!

 

[blake25537]

I have used both the irf520 and the 13n10. The 520 didn't produce the power the 13n10 did but it was a cleaner power. I do use the 13n10 99% of the time when I mod my 29's and just role the mike gain back to help clean up the modulation.

Do you install the 13n10 same as the 520?

 

[blake25537]

how about a update did you get what you want out of the radio

No still working the bugs out. I did do a few changes and got 30 watts out of one. That's the best so far Thanks for asking.

 

[blake25537]

Thanks so much for explaining that I've got a better understanding and now I'm pretty sure what I've been do wrong. Thank you and everyone for taking the time to help me out. Everyone are here is Great people. Thank you all once again...

To finish this up...

Some Radios' provide you a means to apply this mod in a fashion that allows you to keep it simple yet also allow for some "distance" between you and the work the mod tries to perform. It keeps it cleaner and easier to swap or change parts to finish the install and make it work for the different MOS devices you can fit in there.

Ok, See Below...

It's from a PC-68/66 note the Ferrite Bead (L19) and R40 by the Final.
View attachment 33077

Keep the above in mind, the values shown in resistor values is Arbitrary, the Diode is oriented to supply a POSITIVE voltage (note the Band) - meaning I just put them together so you can see the ways you can use the fixed resistance and diode components to accomplish the "rectified feed" and the shunt needed to turn on or off the mess so it won't blow up on you.

Now if you are wise you can double check this by looking into a RFX75 or similar and ask ok, they used these values. Do I need to use them in this?

Yes, and No.

Yes, for the circuit design - so it can provide the power by "sampling" the RF power arriving into the Final from the Driver...

No? Because, the Values you see being used by them for sampling in the amps are for EXTERNAL install amps and are using the values needed BECAUSE THE AMP RECEIVES MORE OUTPUT POWER - so it does not need to "sample as much" to obtain enough power to turn on these parts. Now, if you had an SSB radio - it would be powered by SUPPLIED power to BIAS the part as an extra stage.

In this thread,
You are installing in an AM-only radio and if using the Self-Bias design. This can take more power from the Signal you're trying to amplify hence the cautions issued above to warn you about some inherited limitations from using a self-power bias scheme - you have to take something away to arrive at what is needed to power the Gate properly. Take too much power or waste it in this circuit to obtain a voltage or power level - you wind up destroying or degrading the signal too much and render this effort useless.

So since you're using small signal power feeds, best to use the Jumper shown above. Keeps your design away and "off to the side". However, to protect your work and the GATE of the MOSFET - install a simple low-ohmic value resistor INSTEAD OF THE JUMPER. Have this resistor take it's place. Value to use? Ok, say, 100 ohms to act as a buffer while you sort out the ideal values in the Triad (Resistor-Diode to Resistor-Shunt across) - you'll see power develop using different combinations but each time remember that you can "slam" the Gate with too much power or remove too much signal and arrive to "pinched sounding" results - step back and try again...

• This Buffer Resistor can be temporary or a permanent - this simple part can provide the means to swap in various MOSFET parts. I'm referring to the 13N10FQP response curve compared to a IRF520 - the 13's turn on quicker, but IRF520 provides more linearity. So the Buffer resistor is for the purpose of keeping your work simple yet effectively offering some method to interface and adjust your upgrade.

For those so-inclined, you can remove the Driver and sub in a 2166 and use a 33pF across it's Collector/Emitter to maximize the Miller effect. This swap will idealize the output of the Driver so you don't have to "sample so much of the signal" to obtain any result. Providing a larger power signal, your percentage of sampling requirements is less, which in turn, provides you less degradation of signal going to the Gate because you can use higher - more intrinsic in appearance to the RF signal, high-impedance sampling designs that will take less power from the signal to generate the Gates Turn on voltage as needed.

Good Luck!

 

[Handy Andy]

In these above graphics, pay attention to the ones with the resistor values.

Remember they - these values, are arbitrary - meaning you can change them - as well as where you place them in the circuit.

Look at the Cobra 19 one above, note the 3.3K on the foil side, while another can use a 470 on the foil side. I've seen these done both ways and achieve results.

So this road your on is using a set of rules that are not cast in stone. The principles are there to apply but you have to find what works for you.