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Author Topic: Goodbye tubes.  (Read 6740 times)
K2FW
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Posts: 218




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« Reply #45 on: July 23, 2019, 12:48:35 PM »

Certainly, Bill Orr himself, “Mr. Eimac”
 Wink And the modern, well reasoned article in the reprint bears reading, starting page 24.
An excellent read.  I've had many Bill Orr books over the years.  What I really would like to know is how does the plate dissipation of the FU728F compare to the 4CX1500?  The tube is much larger in size than a 4CX1500.

Are you saying the spec sheets arent sufficient for you?


Please respond when you have something useful to contribute.  Otherwise, just shut up!
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KA4WJA
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Posts: 1098




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« Reply #46 on: July 23, 2019, 02:57:21 PM »

Steven,
Seriously?
Please respond when you have something useful to contribute.  Otherwise, just shut up!
The reason I'm confused (and asking if you're serious or just joking?), is because I was going to point you to some detailed info /discussion....but since Carl gave you the short answer, I thought the long answer might be treated with as much rudeness as Carl's succinct answer.  Sad


I mean, I thought Carl answered you directly 2 days ago...
The REAL rating is 1200W and it took about 2 seconds to find that spec sheet on Google. Since the tube is used for commercial and military amps that is a CCS rating.

You are welcome to apply any ICAS or Hammy Hambone IVAS rating you wish.

Carl


But, taking a chance here...
So, if that isn't sufficient, how about you do a quick search and find the info you desire?
However, perhaps you are unable to do so, and so I will try to be a good ham and point you in the right direction... Smiley


Have a look here for a quite detailed discussion about the FU728F:
https://www.eham.net/ehamforum/smf/index.php/topic,87663.0.html

Or maybe you just want the datasheet (which is allover the internet):
http://www.ok1rr.com/tubes/FU-728F.pdf

Or maybe you'd like some discussion from the contesting reflector:
http://lists.contesting.com/archives//html/Amps/2012-06/msg00315.html


Or maybe all of that doesn't give you what you desire?
So...

So, how about a quick half-dozen bullet-points:
 -- The FU728F has a larger base centering pin, thereby making it incompatible with the 4CX1500b's socket.  But a 4CX1500b will fit in a FU728F socket.

-- The FU728F and 4CX1500b use different filament voltages.

-- The FU728F is less linear than the 4CX1500b, which means even a little too much screen current and you're splattering up/down the band. (even if operated properly, the FU728F isn't the tube to use for clean high-power SSB service, but then again the 4CX1500b is the rare exception for a power tetrode...and depending on how dirty your exciter / transceiver is, perhaps this is a moot point?)

--  Ironically many hams either ignore, or are ignorant of, this poor linearity of the FU728F, but seem to hype this tube's higher gain compared to the 4CX1500b.

-- Remember, if wishing to ignore the poor linearity AND also pushing the tube beyond US legal limits, while it will do this, in addition to you needing to understand how to minimize your transmit IMD, you will need to understand that this is not a 2.5kw CCS tube, no matter how "big" you perceive the anode cooling fins are.

-- (according to anecdotal reports) The FU728F's higher (than the 4CX1500b's) internal capacitance reduces it's gain on the higher HF bands / makes the output tank circuit design more critical.



Now, Steven, I hope this helps....

73,  
John, KA4WJA

P.S.  I gave serious thought to just ignoring you....as I personally feel (just my opinion) that in answering your question after you've been so rude/insulting, could just encourage continued rudeness??
But, taking a chance here.... Smiley


« Last Edit: July 23, 2019, 03:09:26 PM by KA4WJA » Logged
KM1H
Member

Posts: 5253




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« Reply #47 on: July 25, 2019, 09:39:49 AM »

Quote
P.S.  I gave serious thought to just ignoring you....as I personally feel (just my opinion) that in answering your question after you've been so rude/insulting, could just encourage continued rudeness??
But, taking a chance here.... Smiley

I guess he is still on a potty break John Roll Eyes
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K6AER
Member

Posts: 5723




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« Reply #48 on: July 25, 2019, 04:40:39 PM »

Quote:
“-- The FU728F is less linear than the 4CX1500b, which means even a little too much screen current and you're splattering up/down the band. (even if operated properly, the FU728F isn't the tube to use for clean high-power SSB service, but then again the 4CX1500b is the rare exception for a power tetrode...and depending on how dirty your exciter / transceiver is, perhaps this is a moot point?)

--  Ironically many hams either ignore, or are ignorant of, this poor linearity of the FU728F, but seem to hype this tube's higher gain compared to the 4CX1500b.

-- Remember, if wishing to ignore the poor linearity AND also pushing the tube beyond US legal limits, while it will do this, in addition to you needing to understand how to minimize your transmit IMD, you will need to understand that this is not a 2.5kw CCS tube, no matter how "big" you perceive the anode cooling fins are.

-- (according to anecdotal reports) The FU728F's higher (than the 4CX1500b's) internal capacitance reduces it's gain on the higher HF bands / makes the output tank circuit design more critical.”

The FU728F linearity is fine and equal or better than the coveted 4CX1500B.

On my amplifier the IMD from the 2 carrier mix (on 20 and 40 meters)  to the third IMD mix is down 35dB peak to peak. 5th and 7th were down an additional 10-15 dB. These reading were taken at 1700 watts out. Gain on ten meters is about the same as eighty meters at about 14-15 dB. Even in the same amplifier that provides 2.3 Kw on 160-10 meters, the 6 meter output is over 1700 watts. High frequency gain loss is not a function of the tube but of the stray inductance and capacitance in the dual Pi networks. OM Power has developed a better matching network in their amplifier and offer a single tube amplifier for 160-6 meters.

This tube has been in manufacturing for over 25 years. Emtron and OM Power have built many fine amplifiers using this product and the tube holds up fine in high-power contesting. Hams worldwide have been using this tube for many years. I have been using this tube every day for the last three years with no problems.
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NN2X
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Posts: 338




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« Reply #49 on: July 28, 2019, 05:46:20 PM »

The Chinese FU728F Tetrode is rated for 1800 watts continuously and only cost about $400. Gain is about 15-16 dB depending on screen current. I have seen these tubes put out easily 2.3 KW in SSB mode with 60 watts drive. This tube was modeled after the 4CX1500B.
[/quote]

Yep, I had a Emtron DX 3SP, with a pair of those Tubes, and the output on 20 meters, 5KW...PEP..

The price used is about 4,000 (USD)..

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K6AER
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Posts: 5723




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« Reply #50 on: July 31, 2019, 06:40:17 PM »

The Chinese FU728F Tetrode is rated for 1800 watts continuously and only cost about $400. Gain is about 15-16 dB depending on screen current. I have seen these tubes put out easily 2.3 KW in SSB mode with 60 watts drive. This tube was modeled after the 4CX1500B.

Yep, I had a Emtron DX 3SP, with a pair of those Tubes, and the output on 20 meters, 5KW...PEP..

The price used is about 4,000 (USD)..


[/quote]

Is Rudy running still Emtron?
« Last Edit: July 31, 2019, 06:52:09 PM by K6AER » Logged
ZL4IV
Member

Posts: 66




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« Reply #51 on: August 09, 2019, 11:28:28 PM »

Still good support from Rudy and Dan. He made a run of amps last year but haven't looked into what they are up to now. I still service these amps in NZ. In fact these amps are so closely related through the series I was able to point to a fault via email from NA in a DX3-sp, internal connector, the guy just pushed it all the way in, fixed. The FU728F are great tubes and they are clean, as with most issues it's the nut behind the wheel that's loose.

Do you remember the days of AM when there was no 'your off frequency' channelized rubbish, almost no hams had spectrum analyzers. How did we come to this nonsensical debating about perfection. Look for a fault in another and you will find it.
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ZL4IV
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Posts: 66




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« Reply #52 on: August 09, 2019, 11:32:52 PM »

Oh, I forgot to mention the SS Finals do wear out. Something called junction barrier migration. They will eventually go POP!
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W1QJ
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Posts: 2966




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« Reply #53 on: August 10, 2019, 05:38:52 AM »

These tubes sell for even less than $400 if you can buy them direct from China or have some picked up in China.  They seem to have a better record of NOT being problematic like Chinese glass tubes.  At 1500 watts they are actually quite clean and run cool as they do have a large cooling anode structure.  They are tetdrodes and therefore require the screen and bias supplies and associated circuitry to build around them and due to the attract pricing several amplifier companies offer them in their amps.  If a similar tube in a triode was avaialabe at an equal price it would be even better!
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KM1H
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Posts: 5253




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« Reply #54 on: August 10, 2019, 06:14:18 AM »

If only Eimac had released their instant on 3CX1000A7 (actually 1500W PD in normal AB2 Linear use and NOT ICAS) in a version with a 8877 base! What a great tube and bullet proof unlike the 3CX1200 crap variations they sold for decades.

https://frank.pocnet.net/sheets/140/8/8283.pdf

I bought mine as a CH 13 TV translator pull over 30 years ago for the HB 1500W 2M amp. It still will run 1800W key down at the same 100W drive.


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K6BRN
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Posts: 1293




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« Reply #55 on: August 10, 2019, 06:16:16 PM »

Rex (ZL4IV):

Quote
Oh, I forgot to mention the SS Finals do wear out. Something called junction barrier migration. They will eventually go POP!

Transistor wearout curves are time/temperature/voltage dependent.  The exact mechanism varies a bit with transistor type and geometry.  But if properly designed and not (terribly) abused, SSPAs will last decades in continuous use.  Commercial SSPAs routinely last 15+ years at 100% duty cycle with >90% probability of success.

Just one reason why transistors are not plug-in consumable devices in HF amplifiers.

Brian - K6BRN
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ZL4IV
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Posts: 66




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« Reply #56 on: August 10, 2019, 11:18:47 PM »

Exactly, both systems last for decades is used properly. Instant on seems to be an advantage over some non instant on tube types.
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AC2RY
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Posts: 740




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« Reply #57 on: August 11, 2019, 09:49:50 AM »

Exactly, both systems last for decades is used properly. Instant on seems to be an advantage over some non instant on tube types.


Solid state amplifiers are NOT really "instant on". It takes 10-20 seconds to start up control processor and do initial self-check before amplifier is ready to transmit. Though unlike tube amplifiers they have a negligent "stand by" power consumption and thus can be left in that state indefinitely long.
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G3RZP
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Posts: 1271




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« Reply #58 on: August 11, 2019, 01:03:41 PM »

Solid state life is very temperature dependent. Tunnel diodes, for example, being very highly doped, fail generally in ten to thirty years at room temperature, although there are exceptions - that is because of diffusion at room temperature. At Plessey Semiconductors, at the other extreme, we made transistor arrays guaranteed to operate for 30 minutes - at 260C - and medical implant devices intended for over a 20 year life at body temperature.

NASA demanded that test data on space qualified parts be kept for 25 years after delivery. That data was on 15 inch discs....25 years later, I believe that there was one specialist firm in the US who could read such discs and charged accordingly! But data book from those days are still available....
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W1VT
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Posts: 3352




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« Reply #59 on: August 11, 2019, 03:32:45 PM »

I recall that the owners of the old Ten Tec Argonaut QRP rigss loved using the radios so much that they would wear out the finals!  But I don't think anyone really complained considering how much fun they had.  And replacing them wasn't that hard.
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