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Author Topic: FU728F & 4CX1500B Question  (Read 115636 times)
ZENKI
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Posts: 1610




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« Reply #60 on: July 07, 2014, 04:20:21 AM »

If you can afford to build a 30kw PEP output amplifier you can afford to buy a silent 50KVA 3 phase generator. These large generators are readily available
for affordable prices because they are just too big for most domestic users.

In places like the Africa  and the Pacific islands  these private  large generators are common place. In fact since the large scale privatization of power supply assets around the world, and the associated power price market  manipulation; its cheaper to buy these generators than asking the company to connect a full 3  phase system if its not available. There are a number of contest stations in Europe on remote hilltops and farmland  that use exclusive generator power for their stations. Even Solar powered 3 phase  systems are practical and affordable these days. The days  of being held hostage because of the lack of availability  of the 3 phase is fast coming to a end. It was a much fairer  system when the governments ran the  power companies, getting 3 phase was simply making a request and it would be done. Ahhhhh the gold old days!

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K6AER
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« Reply #61 on: July 07, 2014, 01:01:15 PM »

Why would you go to a 3 phase feed unless you are driving AC motors? 30KW is only 125 amps at 240 VAC. Three phase circuits are used in industrial applications for they are more efficient in driving induction motors. Little ransformers don't care.
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W3RSW
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Posts: 602




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« Reply #62 on: July 07, 2014, 04:51:45 PM »

If your building from scratch a three phase full wave rectifier takes less filter capacitance for the same smoothing filter action.  Larger components at higher voltages are fairly expensive. The filter cap is one area to save money.  Then there is the power transformer itself. Never cheap at these demand ratings.

Of course with everything else so expensive, why would that savings interest anyone?  Grin
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Rick, W3RSW
WA7PRC
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« Reply #63 on: July 07, 2014, 09:46:14 PM »

In commercial AM broadcast transmitters your switch speeds are 10-20 MHz.
[snip]
So we are stuck with linear efficiencies or operation in the CW portion of the band.

What used to be KING AM 1090 in Seattle use(s/d) a Gates MW50 50KW transmitter. That xmtr uses switch speeds in their Class D modulator at 75 KHz (good enough for 15KHz audio). The 75 KHz (± the carrier frequency) is trapped-out in the RF output network.  Reference: Section 4 of the MW-50C3 Technical Manual [link].

I wouldn't call operating in the Morse/Digital end of the HF bands being "stuck".  In the most recent Field Day, I operated about equal parts fone and Morse, and had MUCH more fun w/ Morse.  The Morse ops were generally MUCH more efficient. I guess the fone ops were Class A while the Morse ops were Class D/E.  Wink

vy 73 es gl,
Bryan WA7PRC
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G3RZP
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Posts: 1090




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« Reply #64 on: July 08, 2014, 03:54:22 AM »

A conventional 30kW output amplifier is going to want, on SSB speech, about 45kW of AC on average. Assuming  13dB of gain (most of that sort of tx historically used a GG output stage), that's 5kW of drive, or about 7.5kW of AC on average. So we are talking of 50kW out of the mains, plus a not insignificant amount for cooling fans etc. The supply people don't like to have too big a load on one phase, which is why housing estates are arranged with a feed that  puts roughly the same number of houses on each phase.

On key down CW or FSK, there's rather more mains required.
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K8EQ
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« Reply #65 on: April 25, 2015, 07:15:39 AM »

Well considering that I run my pool and it's heater, my two central air conditioners, two refrigerators, my lawn sprinkler system, various other electrical devices and lighting, I doubt that the use of this amplifier will be noticable on my bill.  I also drive a Jaguar and don't wring my hands over the price of gasoline.   I guess that's a British concern.

K8EQ
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W1QJ
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Posts: 2893




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« Reply #66 on: April 26, 2015, 05:00:09 AM »

well this thread has stretched on for over a year now and since then I have had some experiences I can speak to.  First off I had to do several repairs on an Emtron DX4.  It was one problem after another.  No sooner it got all fixed something else came up and I had enough of it and told the owner he is on his own now.  I won't go into all the problems in detail but suffice to say there were several.  However, I will say that when for the short period of time we had it working properly it a most impressive amplifier as far as power output.  The design looks good but attention to assembly details is very poor.  Two problems were directly related to assembly issues and some e better mechanical detail is in order in some places.   The one thing is it is not a good performer on 10 meters due to the 2 large tubes and the tank circuit requirement so it is way down in performance there.  However even that power is sufficient if you except trade off in comparison to the other bands.  Personally I think this particular unit was a "lemon" to begin with.  Problems with interconnecting cables is an issue, but no more than the likes of Alpha (the light show amplifier).  So that cover that part of this discussion.  As to the original post.  I have sitting on my bench right now is what appears to be one of two known Chinese amplifiers here in the US and the only one that is in ham circulation with the other sitting for the last 2 years in limbo.  The one I speak to here is the HF-2013 manual tune version.  This amp runs the FU-728F and the amp appears to be pretty much a 99% "knock off" of the OM-2000 using the same tube.  I talked about the trials and tribulations on another thread.  The amp came to me with a vaporized band switch (the second one to burn up).  I honestly think the last person who worked on it was at fault for this so I can't blame the amp itself.  The amp had a totally different band switch rotor from the factory than the other two replacements sent from China.  I assume the first band switch was just wrong?  Once I installed the third band switch the amp has seen and wired according to the OM-2000 schematic (no doc's provided with the amp)  I assume any doc's is in Chinese.  However I could have used a schematic "as built".  I was in contact with the Chinese rep on this matter and I was told to use the schematic of the OM-2500 as it was supposed to be a "knock off"  of that amp only using a Fu-728 tube which the OM-2000 now uses.  So using those schematics I wired in the third band switch.  As wired the amp would not work on the lower bands and had some issues on the higher bands.  Just did not work right.  Spent hours trying to follow the switching of all the wafers etc.  BTW... the schematic of the OM amps are drawn backwards which complicates things when trying to sort out what gets switch in and out an when.  The schematic is drawn with as if 160 meters is to the full clockwise position and rotates counterclockwise towards 10 meters when in fact the 160 meter band is fully CCW and rotates CW toward 10 meters.  So if a simple thing like that can be overlooked, why not other mistakes?  I concluded that the schematic of those amps are wrong and had to go on my own to get this amp up and running.  I needed almost twice as much lumped C on 160m as was called for and when I added such the amp came alive beautifully.  Now unless the value of the variable capacitor in this amp is a whole lot less than the OM amps, that could be the reason.  The photos look the same however.  Now once the amp is now working I could test it and give a report on the Fu-728 tube.  Into my dummy load I can easily see 2200 watts (as far as I drove it)with 40-45 watts drive or less on some bands with IG2 quite less than the stated max of 50ma.  The worst case was about 35ma and in some instances barely 10ma.  This varied by band.  I see no problem with this amp (if it works right) as being a full 1500 watt amp with plenty of head room to spare.  Oddly the amp uses 2 separate transformers which require two AC cord to the same 240v outlet.  Don't know why they did not combine the two inside the amp?  I don't have the schematic to see if they are in parallel or series and I really don't care.  The HV regulation is fairly normal and the amp has a very impressive blower.  Quite big and should support the claim of key down at 2KW no time limit.  The biggest flaw I see in design is that most all RF connects is done with silver #14 or maybe 12 wire.  I would opt to use silver plated flat stock of 1/4" width if I were to redesign this amp.  the output switching relay seems quite small and not in the order of a Jennings type vacuum relay.  The amp is supposed to have loads of safety shut downs if faulted.  I never was able to get the amp to fault even when the amp would not load due to its inability to operate according to the schematic.  My first impression is that the FU-728 is a promising tube and at 1500w I am sure the IMD is just fine.  At that level it is nowhere near it's limits.  According to OM the plate current trip point is 1.5 amps and 50ma of IG2.  At 1500 watts these values are not even close.  This amp would be hard to compare to a Collins 30s1 as it does not use ground cathode design.  Best I can tell it is swamped grid, however requires much less than 100 watts.   Thank God I did not mistakenly hit it with a full 100 watts.  I would assume it would trip out but did not want to test that.  I found a direct source for this tube at $450.00 US.  That is a damn good price considering US made tubes at this power level.  A redesign of this amp is now available in China with a Pi-Net instead of a pi-L. I think it is just a matter of time that the Chinese get FCC cert. for their amps.  When they do and if they can clean up some of the loose ends they will be a major competitor in the US amp market.  I have already been asked if I wanted to be a distributor when the rime comes.    Be on the lookout in the future.
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N3QE
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« Reply #67 on: April 26, 2015, 05:26:36 AM »

Oddly the amp uses 2 separate transformers which require two AC cord to the same 240v outlet.  Don't know why they did not combine the two inside the amp?

There is an IEC socket and line cord rated for 20 Amps but its not the most common thing in the world. I'm guessing if they couldn't find a correctly threaded UHF jack in China, they couldn't find the 20 Amp IEC connectors either.

Quote
I think it is just a matter of time that the Chinese get FCC cert. for their amps.  When they do and if they can clean up some of the loose ends they will be a major competitor in the US amp market.  I have already been asked if I wanted to be a distributor when the rime comes.    Be on the lookout in the future.

Reminds me of a tale from my youth in a small town, with two butchers' shops. One was advertising pork chops for 29 cents a pound. My mom goes in to that one, and asks, and they're all out of pork chops. So she goes to the other shop and asks them to lower their price from 39 cents to 29 cents a pound to match the competition. The butcher tells my mom "Lady, if I didn't have any pork chops, I'd be selling them for 29 cents a pound too."

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G3RZP
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« Reply #68 on: April 26, 2015, 05:58:55 AM »

Quote
A redesign of this amp is now available in China with a Pi-Net instead of a pi-L. I think it is just a matter of time that the Chinese get FCC cert. for their amps.

I've never managed to get 43dB of harmonic suppression on a Class AB stage with just a pi network. I do not imagine that all the manufacturers using Pi-L networks would be doing so if they could get 43dB from a pi. For Europe, harmonics have to be 43+ 10 log P without needing to exceed 50dB.

 
Quote
The biggest flaw I see in design is that most all RF connects is done with silver #14 or maybe 12 wire.  I would opt to use silver plated flat stock of 1/4" width if I were to redesign this amp.


Or even maybe even a bit wider tape than 1/4 inch, but I agree, wire is not ideal.
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W1QJ
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Posts: 2893




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« Reply #69 on: April 26, 2015, 07:19:10 AM »

Quote
A redesign of this amp is now available in China with a Pi-Net instead of a pi-L. I think it is just a matter of time that the Chinese get FCC cert. for their amps.

I've never managed to get 43dB of harmonic suppression on a Class AB stage with just a pi network. I do not imagine that all the manufacturers using Pi-L networks would be doing so if they could get 43dB from a pi. For Europe, harmonics have to be 43+ 10 log P without needing to exceed 50dB.

 
Quote
The biggest flaw I see in design is that most all RF connects is done with silver #14 or maybe 12 wire.  I would opt to use silver plated flat stock of 1/4" width if I were to redesign this amp.


Or even maybe even a bit wider tape than 1/4 inch, but I agree, wire is not ideal.

Here in the USA for FCC cert all you have to do is make a play on words.  Sure you may not reach that level of harmonic attenuation at 2500 or 2000 watts output without a PI-L network but perhaps at some level lower you can.  That is all based on the fundamental power as to what the related harmonics are down to.  So all they do is to write the manual to state what the acceptable attenuation is at that power level.  The writing of the manual for FCC cert. is at least 50% of the whole thing.  SO you may have to down rate the output power but as we all know no matter what amp is for sale hams will run them balls to the wall just the same.  
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NO9E
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« Reply #70 on: April 26, 2015, 11:52:40 AM »

The purpose of lower power limits in VK and ZL could be to reduce potential of TVI/RFI as many towns/cities are quite compact. Otherwise bands are nearly empty and with simple antennas one can hear many DX with little chance of working. So amps would be useful and IMDs mostly unimportant (due to low ham density).

Lots of news about tetrodes having worse IMD than triods. But one of the cleanest amps in QST reviews was ACOM 2000 using tetrodes. I guess cathode resistors improve linearity.

Ignacy, NO9E
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KM1H
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Posts: 4722




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« Reply #71 on: April 26, 2015, 12:58:05 PM »

Negative FB with cathode resistors and sky high idling current is all it takes to make a very clean tetrode amp.

Now if the Chinese would clone the 4CX600JA/8921 and design another for 1200-1500W PD they would have a real winner. Eimac is a dead horse at that power level and are just holding on selling replacements to the broadcast, TV, and ISM industry.

Carl
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ZL1BBW
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Posts: 1349




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« Reply #72 on: April 27, 2015, 05:50:39 PM »

The purpose of lower power limits in VK and ZL could be to reduce potential of TVI/RFI as many towns/cities are quite compact. Otherwise bands are nearly empty and with simple antennas one can hear many DX with little chance of working. So amps would be useful and IMDs mostly unimportant (due to low ham density).

Lots of news about tetrodes having worse IMD than triods. But one of the cleanest amps in QST reviews was ACOM 2000 using tetrodes. I guess cathode resistors improve linearity.

Ignacy, NO9E
\

ZL now has a 1000 Watt PEP output limit, I think the guys across in VK still have 400 PEP.

All our mainstream TV is now satellite or UHF digital.
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ex MN Radio Officer, Portishead Radio GKA, BT Radio Amateur Morse Tester.  Licensed as G3YCP ZL1DAB, now taken over my father (sk) call as ZL1BBW.
W3RSW
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Posts: 602




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« Reply #73 on: April 28, 2015, 06:44:55 AM »

http://www.g8wrb.org/data/Eimac/4CX600J.pdf

Yes, the 4cx600ja is one nice tube. Note the 600JA's increased anode fin diameter.
 It's been touted on this board before (what, only a couple of weeks ago?  Grin ) so I wonder if anyone's built an RF linear amp using one or two of these ?  Keep in mind the IMD specs are rated from one tone of the two tone test level. Very nice.

Remember those older transceivers that had something like this tetrode as a final, National I think?  A single 4c600JA in the final of an otherwise all solid state xcvr would make a nice rig these days.  It would also eliminate the power wasted in swamping the final's grid from preceding separate radios.

Also Keep in mind it would have to have a 5 minute warm up for the JA's oxide cathode.  I guess a switch could be built in to use the driver immediately on Psk31 or jt65. Grin
« Last Edit: April 28, 2015, 08:30:51 AM by W3RSW » Logged

Rick, W3RSW
KM1H
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Posts: 4722




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« Reply #74 on: April 29, 2015, 06:14:22 PM »

The National NCX-1000 used a single 8122, not the most linear of tubes but adequate. I use mine for some SSB and also for a nice solid 150W carrier on AM where the less than sharp crystal filter gives the audio a nice sound.

I wouldnt mind finding a cheap NIB pair of the 4CX600J's to retrofit into my 6M NCL-2000 where I dont need the wider anode as all that amp will do is about 1300W BUT 6M is a band where a very clean signal is appreciated. The amp currently has a set of Ian, G3SEK's, Tetrode Boards which improved the 8122 IMD about 5 dB; real dB and not ARRL dB.

Carl
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