The AM Forum

This is a prety cool progression of transistor technology... 8)

http://www.youtube.com/watch?v=8ziYqjMQGEQ

Not that it warms the cockles of my heart, but it does have many applications today. :D

In other words, it looks like a solid state device can stand up to the rigors tubes have traditionally done easily.

The BLF578XR is apparently not marketed yet, but it prolly won't be a long wait.

73DG

Probably the one thing that does break is the wallet of the purchaser.

These look very similar to previous issues selling in the $300 range, but at four times the power output (1.2kW per transistor), they may be a bargain if pricing is not scaled by the Watt.

73DG

I've heard estimates of $500 to $700 each.   I'm sticking with 813s $15 - $20 each,  4x1 $40 each...tubes are gg to be around for a while...

Freescale has some competing parts as well:

http://www.youtube.com/watch?v=KZF-FR8b71s&feature=related

and this:
http://www.youtube.com/watch?v=02v58cnb41o&NR=1

Looks to me that SS RF power is really progressing.

Jim
JKO

Cool, thought maybe it has an internal ALC system but looking at the current that’s not apparent. High power MOS of the last ten years or so is generations ahead of the stuff produced in the eighties and nineties. I have worked with the all solid state Rhoades & Schwartz and Comark / Thales television transmitters for a while now and in almost ten years have not had one PA failure. Liquid cooling and power supplies fail, epically the big switching FET in power supplies but not the RF devices although I have never intentionally ran them into a open or shorted load. The Harris broadcast Z line of FM transmitters are designed around interchangeable universal amplifier cards and with four of those transmitters have never had one fail and we get lots of lightning strikes all the time. Same as above, stupid things like the power supplies and control systems fail but not the amplifiers. The Harris Z uses a crazy intelligent power supply that has SCR instead of rectifiers and multiple taps on a transformer with a controller located in the system control to select the correct tap and that’s how they do there regulation of the power supply. Each SCR has its own fuse at its fairly common for at least one in the hundred or so that’s in a 10k transmitter to be blown. To replace the fuses you have to remove the front panel of the transmitter, disconnect several cables including half a dozen double 0 gage cables and role the entire power deck out of the transmitter to get to it because it's always the fuse way in the back in a location that can only be reached with the most difficulty. The amplifier cards are all right under the front and back door and easy to get to, that’s why they never fail. Interesting also that the amplifier assemblies consist of two identical cards mounted on a heat sink between them and will work regardless of how you install them. Right side up or upside down. They fit and work in both directions. There, now you know way more than you ever wanted to about Z line transmitters.
Ray F

Maybe before too long a few of those transistors will start appearing in discarded modules that show up as industrial surplus, as defective PC boards are tossed out, perhaps due to the failure of a minor component like a resistor. Less and less repair work is being done at the component level these days, and some companies might scrap and replace the entire module instead of repairing it.

Don,
Modules appear all over the place. I saw a bunch at Deerfield last spring.
I've been running a modified MRI amp for a while now and have a pair of 1.2 KW amps to build into a linear.  Even the older stuff MRF150s still work great.
Voltage ratings are going up and soon QRO will be easier.

I'll stick with FQA11N90s at $4.00 each for now, although eventually there will be much better parts available at a similar price...... I could build a KW transmitter with the cost of the power I'd consume in 1 year if I ran a typical tube KW transmitter in my shack.  Yes, the power in my area is unbelievably expensive and I often have the transmitter on all day.  I got a $200 electric bill back in 1975 for *1 MONTH* (and power was much cheaper in 1975) when I was running my pair of 304TLs modulated by 833As.  This is what started me on looking for a far more efficient alternative to high power AM - and one that, when I was not transmitting, would consume virtually no power.

Good point on the op cost.  It could be a dealbreaker in the QRO choice for many less-monies of us. :(

73DG

I saw that it was liquid cooled and I wonder how this constrains (coolant temp) the application ... electromigration is still electromigration

Steve beat me to it. There is a $4 x 8 SS alternative to 813s for RF and it's 20% more efficient.

The RF efficiency when transmitting is definitely more efficient.  But, it's the OVERALL efficiency that really makes a solid state transmitter the winner.

Let's say you're on the radio for 5 hours some night.  This is not atypical - at least not around here  :D  Let's say you're running a KW output with a pair of 4-400s modulated by 833As.  The RF driver is a Valiant and the audio driver is a pair of 2A3s with tube rectifiers, etc.

The RF amplifier tubes use 5 volts @ 14.5 amps each - so that's 5 volts @ 29 A for the RF amp.  The modulators are 10V @20A (for both tubes).  Then there's the Valiant - let's say it consumes about 100 watts in standby.  That is probably being very optimistic, but what the heck!  We'll say the audio driver uses about the same.  So what's the stand by power budget? 

145 watts for the RF finals.  200 Watts for the modulators.  200 watts for the RF and audio drivers.  So we're burning up about 545 watts *IN STANDBY*. 

You've consumed about 2275 watt-hours for doing nothing.  Transmitting power input is not included at this time.

Your solid state rig might consume 20 watts in standby, so you'll consume 100 watt-hours in the 5 hours you're on the air - when in stand-by.  Based on this along, the H.B. solid-state rig is 20 times more efficient, and I didn't add in the plate losses, etc... which will push the efficiency higher.

The difference is really quite amazing.