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Author Topic: 3CPX1500A7 Eimac ProTek MKS  (Read 13250 times)
K6CKD
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Posts: 170




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« on: December 22, 2014, 10:47:25 AM »

We know that hams seem to favor Eimac.  We also have Pro Tek and MKS out there. They are being used in the MRIs. (magnetic resonance)
Three different brands for the CPX. Is there a difference in reliability?  Is there an insider here on Eham that actually knows about the reliability and longevity of these two other brands as compared to expensive Eimac? Undecided
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W3RSW
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Posts: 606




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« Reply #1 on: December 22, 2014, 11:57:06 AM »

May not matter since purchasing agents and bean counters make the purchasing decisions. Engineers and managers used to, but those days have disappeared into the "budgeting" and quarterly report maw.

I personally buy Eimac since I'm an independent amateur and have very few equipment with which to experiment.  It appears to be a lifetime investment for me and what few I have are very reliable.

So far the pair of 8875's I bought in the 80's are still yielding full output in my homebrew amp., - Updated with GM3sek's triode control board. I expect the pair of 3cx800a7's acquired not to long ago to last the same in rotation with an older, slightly degraded pair that came with a used commercial amp.

Time will tell for the newer and now supposedly better Chinese tubes. Except for gross defects covered under warranty, the ones that last don't really have enough time  yet for long term comparisons. I understand that emissions of some of the later built of these actually exceed som Eimac originals.

Perhaps I got Eimac's simply because they're American made... Whole host of reasons to feel better just having them, but if I were a commercial buyer I'd almost have to try some Chinese from RF Comcepts, etc. to see if recent batches are more reliable.  Since medical people may change them out on a time rather than degradation basis, it may be cost effective for a tube's first service lifetime, but would I'd be in line to pick up the used ones?  ..um, not sure.
Your probably not going to get dead nuts certain answers but you already knew that.  Grin
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Rick, W3RSW
W1QJ
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Posts: 2984




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« Reply #2 on: December 22, 2014, 05:48:54 PM »

I have a new MKS tube 3CPX1500a7 I just put in my AL-1500. It works fine, no problem.  How long it will last I don't know, but it works just fine
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KM4AH
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Posts: 963




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« Reply #3 on: December 22, 2014, 06:58:18 PM »

I bought a couple of Eimac  8877's back in the early nineties. They were from a batch that Surplus Sales had for $975 per matched pair. One of those shorted in about six months. They had some bad runs and I don't know that I have all that warm and fuzzy a feeling about Eimac.
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ZENKI
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Posts: 1648




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« Reply #4 on: December 23, 2014, 08:47:13 PM »

Has anyone measured the IMD performance of any of the Chinese 8877 tubes and compared the figures to a Genuine Eimac 8877?

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KG9SF
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Posts: 282




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« Reply #5 on: December 29, 2014, 04:58:32 PM »

Yes.  After the 27th harmonic they exceed the gen-yew-wine eimacs.
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KD0REQ
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« Reply #6 on: December 29, 2014, 06:16:14 PM »

I want one of those magnifying glasses, I keep losing stray positrons in the rug...
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KK5DR
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« Reply #7 on: January 19, 2015, 06:05:20 PM »

I can't speak of the "CPX" tubes, however I have tested the ProTek 8877 and a genuine EIMAC 8877 in the same amp, and found them to be virtually identical. All performance parameters were identical.
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W1QJ
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« Reply #8 on: January 20, 2015, 03:58:59 AM »

Has anyone measured the IMD performance of any of the Chinese 8877 tubes and compared the figures to a Genuine Eimac 8877?



On Zenki's headstone.....HERE LIES "ZENKI" KING OF THE IMD FRONTIER
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NO9E
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Posts: 888




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« Reply #9 on: January 20, 2015, 08:49:01 AM »

Quote
Has anyone measured the IMD performance of any of the Chinese 8877 tubes and compared the figures to a Genuine Eimac 8877?

IMD of a triode amplifier in GG design depends largely on gain of the tube + stability of PS. This is because GG provides a linearizing feedback that is stronger with higher gain. If gain of any 8877 version is high and PS is stable, IMD when not overdriving will be low.   

Ignacy, NO9E
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N3QE
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Posts: 5595




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« Reply #10 on: January 20, 2015, 09:26:15 AM »

Quote
Has anyone measured the IMD performance of any of the Chinese 8877 tubes and compared the figures to a Genuine Eimac 8877?

IMD of a triode amplifier in GG design depends largely on gain of the tube + stability of PS. This is because GG provides a linearizing feedback that is stronger with higher gain. If gain of any 8877 version is high and PS is stable, IMD when not overdriving will be low.   

Bias must be important too :-). IMD of an amp biased heavy into class C for cw usage would be very ugly.

Large zero-signal idle current (as recommended by tube manufacturer) doesn't hurt either! Ameritron has the tube dissipating circa 800 watts with no signal, when their AL-1500 is biased for SSB mode!
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ZENKI
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Posts: 1648




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« Reply #11 on: January 22, 2015, 12:23:45 AM »

Thats true but what I am specifically asking is that in the same amp and under the same drive conditions is  IMD the same as a Eimac 8877. Has anyone measured a genuine 8877 and compared it to a  Chinese 8877 and compared the results. I am curious.


Quote
Has anyone measured the IMD performance of any of the Chinese 8877 tubes and compared the figures to a Genuine Eimac 8877?

IMD of a triode amplifier in GG design depends largely on gain of the tube + stability of PS. This is because GG provides a linearizing feedback that is stronger with higher gain. If gain of any 8877 version is high and PS is stable, IMD when not overdriving will be low.   

Ignacy, NO9E
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ZENKI
Member

Posts: 1648




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« Reply #12 on: January 22, 2015, 12:27:29 AM »

Thats all fine however has anyone compared a genuine Eimac 8877 and Chinese 8877 under the same  bias conditions?

The story I have been told is that the Chinese Manufacturer of 8877's was originally a manufacturing contractor who  went solo after the contract run or when Eimac ceased producing in china. If that is the case then then Chinese 8877's might be identical to the Eimac tubes in terms of performance. Alpha Amplifiers offers you the opportunity to buy either brand of tube, besides the price it would be nice to see some IMD data.

Quote
Has anyone measured the IMD performance of any of the Chinese 8877 tubes and compared the figures to a Genuine Eimac 8877?

IMD of a triode amplifier in GG design depends largely on gain of the tube + stability of PS. This is because GG provides a linearizing feedback that is stronger with higher gain. If gain of any 8877 version is high and PS is stable, IMD when not overdriving will be low.   

Bias must be important too :-). IMD of an amp biased heavy into class C for cw usage would be very ugly.

Large zero-signal idle current (as recommended by tube manufacturer) doesn't hurt either! Ameritron has the tube dissipating circa 800 watts with no signal, when their AL-1500 is biased for SSB mode!
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ZENKI
Member

Posts: 1648




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« Reply #13 on: January 22, 2015, 12:30:51 AM »

Well do you want your epitaph to read "here lies the splattering lid who did not give a damn and was too technically  ignorant to give a damn, may he splatter in peace"Huh??

Has anyone measured the IMD performance of any of the Chinese 8877 tubes and compared the figures to a Genuine Eimac 8877?



On Zenki's headstone.....HERE LIES "ZENKI" KING OF THE IMD FRONTIER
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DL8OV
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Posts: 1059




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« Reply #14 on: January 22, 2015, 02:00:37 AM »

I agree with Zenki regarding the issue of transmit IMD

My own particular interest is receiver front ends. Manufactured rigs routinely have an MDS of -73 dBm and I have a design on my bench right now that goes down to -78dBm MDS. All of these efforts however go to waste if I am trying to copy a signal down in the noise and somebody with -26 dBm 3rd order IMD parks their transmitter 4 KHz away.

WE need to clean up our bands, what are YOU willing to do to help?

Peter DL8OV
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