I've put my FET amps to the side for the moment, but yeah, the price is not bad and they are a good match for higher powered radios to get you a little more power out. They DO need a fan. Pout drops drastically as they heat up. I cracked open a ERF7530 mosfet, was not impressed, little tiny cheap die. Nothing like the mosfets we use in car stereo amps, dies where 3 times at least, bigger than the die in the 7530, and had copper tabs etc, not cheap alluminium tabs like the ERF7530 die is attached to. Stick with your pill amps if possible, and hope that ASI steps up production of their copy-cat devices to replace the discontinued 30Mhz and down devices.
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Palomar 450HD Fet
- Thread starter truckbeater
- Start date
Toll_Free
Well-Known Member
The ERF devices where NEVER designed for RF service.
They are designed for switch mode power supplies, if I remember correctly.
Mr Bulldog Wattmeters just found another way to make profit.
Not many people that KNOW how to interpret what they see on a scope... And using an exciter tuned for 100 percent modulation will EVER recommend an EFJ device to a customer. At least not one in the same town as they are in!!!!
--Toll_Free
They are designed for switch mode power supplies, if I remember correctly.
Mr Bulldog Wattmeters just found another way to make profit.
Not many people that KNOW how to interpret what they see on a scope... And using an exciter tuned for 100 percent modulation will EVER recommend an EFJ device to a customer. At least not one in the same town as they are in!!!!
--Toll_Free
Fixed. And yes, mosfets designed for switching do not work for RF amplifiers very well. Mosfet "pills" however work fine, they are designed to do the job of "gain" rather than "switching".
You get my PM TF?
Hi Toll,
I'm not so sure.
They work just fine at 1MHz
I manufacture and sell this stuff for a living although these are not from my products but from two US companies:
4-pill
8-pill (1500W)
Phil Unit 148
London, England
I'm not so sure.
They work just fine at 1MHz
I manufacture and sell this stuff for a living although these are not from my products but from two US companies:
4-pill
8-pill (1500W)
Phil Unit 148
London, England
BTW, that latter photo is from a Harris 50kw Am TX and is a photo from one of the 50 PA modules in the WABC transmitter.
Phil Unit 148
London, England
Phil Unit 148
London, England
Toll_Free
Well-Known Member
Phil,
I speak regularly with someone running the OLD WABC transmitter on 75.
Those 'switchmode' transmitters are a trip. I've worked on one before, JUST one. Not real common.
Those 600 watt modules should be run as 40+ modules, half for positive peaks, half for negative. They run a single A/D converter, then run the OUTPUT of the A/D converter into these modules....... Years ago, we did it with resistive dividers.... Nowadays, SOC (System On a Chip).
I have a Harris TX like this, although I don't think it will ever be on amateur bands... Well, I have a Harris exciter.... And the matching amplifier. It's from the 80s, currently they just use the 600 watt modules in series.
Interesting methodology.... Kind of makes tubes absolete. ALSO, if you 'blow a pill', the 'next' amplifier board just takes the place. Instead of losing 40+ kw output, you lose about 600 watts PEP.
At 1 mhz, you're running those transistors where they are SUPPOSED to be run at, Phil. There is a HUGE difference when running an IRF medium wave switchmode device at 1000 Kc vs 27,000 kc. Like, the diff between Class AB and Class H.
Kinda like running an SD1446 at 4 mhz. Yeah, they WILL work... BUT, I don't see many switchmode harris transmitters running those same IXYs devicies or IRF's at 29 mhz, 26 or even the 27 ISM band or in the plasma generator.
They make FINE transmitters where they where designed. The problem is when CBers try to do "switchmode' transmitters using devices never designed for it. The devices designed for RF LINEAR amplification ain't cheap!
--Toll_Free
I speak regularly with someone running the OLD WABC transmitter on 75.
Those 'switchmode' transmitters are a trip. I've worked on one before, JUST one. Not real common.
Those 600 watt modules should be run as 40+ modules, half for positive peaks, half for negative. They run a single A/D converter, then run the OUTPUT of the A/D converter into these modules....... Years ago, we did it with resistive dividers.... Nowadays, SOC (System On a Chip).
I have a Harris TX like this, although I don't think it will ever be on amateur bands... Well, I have a Harris exciter.... And the matching amplifier. It's from the 80s, currently they just use the 600 watt modules in series.
Interesting methodology.... Kind of makes tubes absolete. ALSO, if you 'blow a pill', the 'next' amplifier board just takes the place. Instead of losing 40+ kw output, you lose about 600 watts PEP.
At 1 mhz, you're running those transistors where they are SUPPOSED to be run at, Phil. There is a HUGE difference when running an IRF medium wave switchmode device at 1000 Kc vs 27,000 kc. Like, the diff between Class AB and Class H.
Kinda like running an SD1446 at 4 mhz. Yeah, they WILL work... BUT, I don't see many switchmode harris transmitters running those same IXYs devicies or IRF's at 29 mhz, 26 or even the 27 ISM band or in the plasma generator.
They make FINE transmitters where they where designed. The problem is when CBers try to do "switchmode' transmitters using devices never designed for it. The devices designed for RF LINEAR amplification ain't cheap!
--Toll_Free
You're right of course.
Interesting as you say on the big boxes. An alarm lights comes on and one can hot swap a 1kw+ module without the listener even noticing.
I think Nautel have done away with the modulator these days all up there in class-E or whatever and so very efficient:
Their latest 50kw: NX50
Anyways, back to plastic FET's.
When we produced PA pallet & modules we tamed several IRF510's to comfortably work fairly flat across the FM broadcast band (88-108MHz) and on the bench had 100W out of a pair in class-C.
How many cents are those rascals these days. Maybe they even give them away with KFC.
I'm waiting for one of your US amp builders to get to grips with keeping their FET's cool and to produce a clean 1kw carrier power from a 14V rail.
That would suit me just fine as I intend investing in one of the Kenwood 200w pep mobile rigs when funds allow.
Take care.
Phil Unit 148
London
England
Interesting as you say on the big boxes. An alarm lights comes on and one can hot swap a 1kw+ module without the listener even noticing.
I think Nautel have done away with the modulator these days all up there in class-E or whatever and so very efficient:
Their latest 50kw: NX50
Anyways, back to plastic FET's.
When we produced PA pallet & modules we tamed several IRF510's to comfortably work fairly flat across the FM broadcast band (88-108MHz) and on the bench had 100W out of a pair in class-C.
How many cents are those rascals these days. Maybe they even give them away with KFC.
I'm waiting for one of your US amp builders to get to grips with keeping their FET's cool and to produce a clean 1kw carrier power from a 14V rail.
That would suit me just fine as I intend investing in one of the Kenwood 200w pep mobile rigs when funds allow.
Take care.
Phil Unit 148
London
England
Toll_Free
Well-Known Member
You're right of course.
Interesting as you say on the big boxes. An alarm lights comes on and one can hot swap a 1kw+ module without the listener even noticing.
I think Nautel have done away with the modulator these days all up there in class-E or whatever and so very efficient:
Their latest 50kw: NX50
Anyways, back to plastic FET's.
When we produced PA pallet & modules we tamed several IRF510's to comfortably work fairly flat across the FM broadcast band (88-108MHz) and on the bench had 100W out of a pair in class-C.
How many cents are those rascals these days. Maybe they even give them away with KFC.
I'm waiting for one of your US amp builders to get to grips with keeping their FET's cool and to produce a clean 1kw carrier power from a 14V rail.
That would suit me just fine as I intend investing in one of the Kenwood 200w pep mobile rigs when funds allow.
Take care.
Phil Unit 148
London
England
Phil,
The issue here is, class C is not linear amplification. As soon as you start applying enough bias for linear amplification, you'd need peltier junctions to keep the individual devices cool. And at that point, you'd be right back up to the cost of 2879s, and a single 2879 does a HELL of a lot more Pout, CLEANLY (read this, biased class AB) than a single IRF5x0, at least that I've been able to extract....
When you ONLY are amplifying a carrier (or FM), it's EASY to build clean class C, harmonics are canceled if the output xformers are built correctly and completely in balance, and even order pretty much takes care of itself (I'm being VERY simplistic here for the sake of discussion) with the FM signal....
BUT, I am impressed that you guys could get them to work there, as well as the power output involved!
Another issue involved is if you DON'T use a pelteir or other VERY efficient cooler (maybe a single PC liquid cooling system with MULTIPLE pads and in/out would work, but then again, you lose the cost bennie of the FETS when you're purchasing a 300 dollar cooling system and adding on 16-32 cooling pads, the associated plumbing, etc.), then your keydown time is VERY limited.... As soon as those FETS start heating up, Pout DDDRRROOOPPPPPSSSS down. And ANY amount of bias close to bringing it to linear amplification is going to get a normal heatsink PLENTY warm... And don't get me started on the fact not a SINGLE amp builder today uses copper heat spreaders... Factor that cost in (which is WORSE here, since your gubmint owns nearly all the copper mines), and your ABOVE the cost of 2879s.
HOWEVER, I do believe that Class E-H is the way to go, if you want AMPLITUDE MODULATED signal cheaply with these kinds of devices... The issue in the mobile would be getting enough Vsource... Maybe one of the motormaul type devices? With a 28 volt charging system, class E modulator, it MIGHT be doable. Probably be EASIER and less expensive to attempt to PWM a high power inverter as the modulator, though. I have a couple 3 amp power supplies here that have line level inputs in them. Vout is the carrier control, and then it will modulate cleanly to about 22 volts. I keep the carrier about 4
That's something else you could try, is modulating a 12 volt power supply, but again, you're limited to the 14 volts at the alternator..... A 28 volt system would be IDEAL.... You could also try modulating a car stereo amp..... Some of these FET amps MIGHT have devices that could go this high... And car audio amps generally have MORE devices than necessary to get the job done, so they don't heat up. Might be the cheapest way to get there.Wheres that amp Dennis redid? Throw that in the mow-beel and be done with it.
You have any old transmitters sitting here stateside that need to be 'parted out' ???
I'd like to find somethin small to play with, maybe even somethin like designed for the tropical bands, one of the 100 watt religious station boxes would even be cool. Want to convert to 160 or 75.... Unless it's a tropical unit, then prob 40 or 20.--Toll_Free
I don't have any old broadcast transmitters lying around on your side of the pond. I do have a solid state kilowatt unit that's waiting for a new home.
I have a friend who buys up AM stations in fire sales.
If I hear of something I'll pm you.
Unit 148
I have a friend who buys up AM stations in fire sales.
If I hear of something I'll pm you.
Unit 148
They get hot but!!
They do get hot but its nothing a good 12V fan wont fix in your car or truck. I have a home built MofFet amp based off the FET 450HD that does right at 1100w and its a base plus I run a 450 FET HD in my truck. They do great for the money but need to be kept cook. I used mini fans on my FET 450 in my truck, drilled holes in the heat sink and use the fans to pull the air threw the heat sinks. I have a digital thermomitor that I can read on my dash as well. I am a Ham and CB lover plus a tech to boot but all these mods can be done by the average radio guy and a simple 12V fan will work great. The thing to remember is to not have to much key down time! 10to15 seconds is good. 20 to 30 seconds , not so good! Good part about extended key down is that the mosfets can be replace by a novice radio guy for less than $15.00!! I also run a DX94HP with my 450 FET HD!