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Using IRF530 outputs and 2N3553 drivers in ubitx

 

Well, according to the datasheet:
Input C 180 pF
Output C 81 PF
Reverse transfer C 15 pF.
So if we drive the gate, we have 180 +15(1+Av) pF
Av being the voltage gain.
If we drive the source, we have 180 + 81 pF so depending on the gain, the input capacitance is not hugely different in either configuration. However, you have the same current in the source as in the drain, so you need to supply all the current from the driver that appears in the output. Its much easier to drive the gate then the source. So Allison is correct in that the impedance would need to be very low, a step down transformer would be needed to drive the source and still a lot of current would be needed to drive the transformer. Pick your poison. I like the grounded source better.

Quoting Howard Fidel <sonic1@...>:

Yes, but there is no Miller capacitance so the total is less.
Quoting Brian <vk4bap@...>:

Is the reason for not using power MOSFET's in grounded gate the high drain-source capacitance? Looking at the IRF510 datasheet it looks like drain-source capacitance is higher than gate-source. Have I read that correctly?

Brian VK4BAP
Rahul Srivastava
 

Thanks..!!? Alison for the detailed analysis. Just to scratch the itch maybe I will hook up one in mid air with a 25:1 transformer at input and standard bifilar on drain.?

I once made 3x3 pushpull on IRF510 running at 30V for? 27.120Mhz ISM band freq got pretty decent 150W output. Input was on binocular core and output on stacked Mix 6 toroids.?

73

Rahul VU3WJM
 

After I wrote the last email, I realized the cascode configuration is much better.
It needs 2 more FETs but you drive the gate of the first one, and it provides the drive to the second one and the second one's gate is AC ground. I can't do it now, but I will see if I can find time to design one next week.
If you wanted to do this with uBitx, remove the exiting output xformer, add 2 IRF530 and a higher voltage supply, with a new output transformer. Should get up to 50W easily without changing the driver.
Howard
Quoting "Rahul Srivastava via Groups.Io" <vu3wjm@...>:

Thanks..!!? Alison for the detailed analysis. Just to scratch the itch maybe I will hook up one in mid air with a 25:1 transformer at input and standard bifilar on drain.?
I once made 3x3 pushpull on IRF510 running at 30V for? 27.120Mhz ISM band freq got pretty decent 150W output. Input was on binocular core and output on stacked Mix 6 toroids.?
73
Rahul VU3WJM
 

At the level of 100 watts, it makes immense sense to just go with MRF150 or one of the higher end mistuibishi devices. The IRF series are very prone to oscillations. They are gratifyingly well behaved on the bench with a dummy load. They go wild with the antenna.
My favourite configuration for more than 100 watts is actually a bit of steam-punk. You can pick two 6146Bs for 10 dollars off a good online supplier. I bought several from last year's Dayton schelp. A valve amplifier will be very forgiving with SWRs, it has a sparkling SWR, it uses air wound coils. Surely, the power supply is a big of a challenge, but not really. The audio aficiondos have rejuventated the supply of high voltage transformers. A great linear amplifier with two 6146Bs will serve you and your kids for a long long time. I am going to rebuild my double-807 job to these tubes soon.

- f??

On Sat, May 19, 2018 at 8:53 PM, Howard Fidel <sonic1@...> wrote:
After I wrote the last email, I realized the cascode configuration is much better.
It needs 2 more FETs but you drive the gate of the first one, and it provides the drive to the second one and the second one's gate is AC ground. I can't do it now, but I will see if I can find time to design one next week.
If you wanted to do this with uBitx, remove the exiting output xformer, add 2? IRF530 and a higher voltage supply, with a new output transformer. Should get up to 50W easily without changing the driver.
Howard
Quoting "Rahul Srivastava via Groups.Io" <vu3wjm=[email protected]>:

Thanks..!!? Alison for the detailed analysis. Just to scratch the itch maybe I will hook up one in mid air with a 25:1 transformer at input and standard bifilar on drain.?
I once made 3x3 pushpull on IRF510 running at 30V for? 27.120Mhz ISM band freq got pretty decent 150W output. Input was on binocular core and output on stacked Mix 6 toroids.?
73
Rahul VU3WJM


 

¿ªÔÆÌåÓý

I've been reading for some time about the possibility of increasing the power of uBitx transceivers. Originally, the device seemed to be intended for OM experimenters to make QRP traffic. I think that wanting to traffic with a power greater than twenty watts away a little from the spirit QRP. That's just my opinion. When I see that when some people are doing local QSOs with linear kilowatts I wonder. They may not have a well tuned antenna for the band they are trading on. It is not surprising that they have their correspondent repeat several times and that in the end they announce 59 +++.
What do you think ? I wonder because I just decided to switch to QRP traffic and I decided to stop the kilowatt hunt and the price of these amplifiers.

Gilles F1BFU the happy owner of an unmodified uBitx

Le 19 mai 2018 ¨¤ 20:42, Ashhar Farhan <farhanbox@...> a ¨¦crit :

At the level of 100 watts, it makes immense sense to just go with MRF150 or one of the higher end mistuibishi devices. The IRF series are very prone to oscillations. They are gratifyingly well behaved on the bench with a dummy load. They go wild with the antenna.
My favourite configuration for more than 100 watts is actually a bit of steam-punk. You can pick two 6146Bs for 10 dollars off a good online supplier. I bought several from last year's Dayton schelp. A valve amplifier will be very forgiving with SWRs, it has a sparkling SWR, it uses air wound coils. Surely, the power supply is a big of a challenge, but not really. The audio aficiondos have rejuventated the supply of high voltage transformers. A great linear amplifier with two 6146Bs will serve you and your kids for a long long time. I am going to rebuild my double-807 job to these tubes soon.

- f??

On Sat, May 19, 2018 at 8:53 PM, Howard Fidel?<sonic1@...>?wrote:
After I wrote the last email, I realized the cascode configuration is much better.
It needs 2 more FETs but you drive the gate of the first one, and it provides the drive to the second one and the second one's gate is AC ground. I can't do it now, but I will see if I can find time to design one next week.
If you wanted to do this with uBitx, remove the exiting output xformer, add 2? IRF530 and a higher voltage supply, with a new output transformer. Should get up to 50W easily without changing the driver.
Howard
Quoting "Rahul Srivastava via Groups.Io" <vu3wjm=[email protected]>:

Thanks..!!? Alison for the detailed analysis. Just to scratch the itch maybe I will hook up one in mid air with a 25:1 transformer at input and standard bifilar on drain.?
I once made 3x3 pushpull on IRF510 running at 30V for? 27.120Mhz ISM band freq got pretty decent 150W output. Input was on binocular core and output on stacked Mix 6 toroids.?
73
Rahul VU3WJM
 

Farhan,

A pair of 6146s at 800V will do an easy 100W out and fairly clean as well.? They
will need about .5 to 1W if grid driven.? However they cannot be wideband so you need
band switching at the output and to avoid needing neutralization both good construction
to keep the input and output well isolated plus heavy loading of the grid.? I have old iron?
like: Hallicrafters Ht37, National NCX-3, Heathkit HW101 and Tempo-One(fitted with 6146s).

Of course the 4CX250 is common and fairly cheap, tw are a full KW.? The 2000V .5A
power supply is a project.? That and a good 50 CFM at 1 inch of pressure blower.
Bet they will do 600W all day easy.? Grid driven 2-4W is enough class AB1, more like
6w for Class C CW.

If I'm using MRF150 then go for the capability by that I mean 300W for a pair P-P.
A 48-50V supply at 13-14A should do it.? ?However they also require good care in
design or you get a good power oscillator. drive them with 2-4 watts more runs
the risk of frying the Gates.? Amps like that are a lot of machine work as the heat
sink copper heat spreader to move the heat and PCB are often a unit when done.?
Done that as well.? Beware of MRF150 junk parts, known good are about $100.
WIth all the fans and power indicators and such expect another $$$ or more.

Allison

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