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Author Topic: Tube vs. SS / Amplifier IMD Tests / Tirode vs. Tetrode vs. Solid-State  (Read 48530 times)
KA4WJA
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« on: December 25, 2014, 11:20:58 AM »

With all the recent discussion of "tube amps vs. solid-state amps", "linearity", and "IMD / spectral purity", etc., I set-out to get some hard numbers (from the tube manufactures and ARRL product test reviews), and thought some here might find them useful / educational, as well as insightful!!!

As we already covered the discussion of the mediocre-at-best transmit IMD and transmit spectral purity of our recent/modern ham transceivers here...
http://www.eham.net/ehamforum/smf/index.php?topic=97093.0
 I thought some might also like to look at some facts about the IMD specs of our amplifiers... 



1)  First off, some clarifications....
--- I may have missed some modern amps, and those "classic" ones that are still running strong 40 - 50 years on (L4B, Henry's, Collins, Swan, old Heaths, etc.), but I've included only the ones that I have ARRL product reviews of (giving all of us some independent and verifiable facts to compare)...

--- I also included the exact tube specs (from manufacture data sheets) for some of the popular tubes, so you can see what might be produced by various tubes in various amps that are not listed here...

--- Since the ARRL does all their IMD reporting in "db below PEP" / db (PEP), and not dbc, all numbers here listed as "db" are "-db (PEP)"....and any "dbc" figures are notated as such....

--- All IMD specs are 3rd / 5th / 7th / 9th order products, in that order....
(tube data sheet specs only show 3rd / 5th...)



2)  Here are some tube data sheet specs...
8877/3cx1500a7  =  -46 / -47  (-40dbc/-41dbc) at 2700vdc anode
8877/3cx1500a7  =  -44 / -47  (-38dbc/-41dbc) at 3500vdc anode
        3-500z        =  -46 / -52  (-40dbc/-46dbc)
        3cx800       =  -42 / -38  (-36dbc/-32dbc)
4cx1500b           =  -49 / -53  (-43dbc/-47dbc)
GU74b/4cx800    =  -34 / -34  (-28dbc/-28dbc)

And, here are links to the data sheets these specs were taken from...

http://ekladata.com/0JUqgv3JKRG1MKOflCO23q54M5Q/3CX1500A7.pdf

http://www.tubecollectors.org/eimac/archives/3500z(73).pdf

http://www.g8wrb.org/data/Eimac/3CX800A7.pdf

http://www.tubecollectors.org/eimac/archives/4cx1500b(66).pdf
http://www.g8wrb.org/data/Eimac/4CX1500B.pdf

http://www.qro-parts.com/images/pdf_files/GU74B.pdf
http://frank.pocnet.net/sheets/018/g/GU74B.pdf




3)  Now, onto the nitty-gritty....what IMD products do our amps produce...
At their rated maximum output, or at 1500 watts out, WITHOUT being OVERDRIVING....(and overdriving is unfortunately done a lot, especially with amps not designed for "full-legal-limit"...)

Also I've added some detail about tube compliment....and if available in the product review, what SWR the amp is spec'd to operate into at max ratings...


Alpha 9500 (1x 8877/3cx1500a7) =  45/49/56/57  (at up to 3:1 SWR)
Alpha 8410 (2x 4cx1500b's)         =  ... no ARRL test yet...
Alpha 8100 (2x Gu74b/4cx800's)  =  52/48/53/61  (at up to 3:1 SWR)
Alpha 87a (2x 3cx800's)               =  50/46/65/62   "            "
Alpha 89  (2x 3cx800's)                =  42/45/61/59   "            "
Alpha 91  (2x Gu74b/4cx800's)     =  45/49/57/64   "            "

Acom 1000 (Gu74b/4cx800)         =  44/55/55/60   "            "
Acom 1010 (Gu74b/4cx800)         =  37/53/56/62   "            "
Acom 1500 (4cx1000a)                =  33/39/50/55   "            "
Acom 2000A (2x Gu74b/4cx800's)=  37/60/61/60   "            "

Ameritron AL-82 (2x 3-500z's)      =  38/54/53/53  (typ up to 3:1 SWR)
Ameritron AL-811 (3x 811a's)       =  40/46/56/58
Ameritron AL-800H (2x 3cx800's)  =  49/55/63/63
Ameritron ALS-600 (50v FET's)      =  30/40/42/48  (up to 2:1 SWR)
Ameritron ALS-1300 (50v FET's)    =  38/43/54/49  (up to 2:1 SWR)

Commander HF-1250 (3cx800)      =  46/44/52/57
Commander HF-2500 (2x 3cx800's)=  53/56/58/60

Emtron DX-1d (Gu74b/4cx800)      =  37/46/56/60   (up to 2.5:1 SWR)

Heathkit SB-221 (2x 3-500z's)       =  35/48/61/63

Kenwood TL-922a (2x 3-500z's)     =  38/54/48/50

OM2500A (Gu84b/4cx2500a)         =  43/44/60/56  (up to 2:1 SWR)

QRO HF2500dx (2x Gu74b/4cx800's)=  43/40/57/60

SPE Expert 1K-FA (50v FET's ?)     =  42/43/49/56  (built-in autotuners, handle
SPE Expert 1.3K-FA  (Huh)             =  no ARRL test yet    up to 3:1 SWR)
SPE Expert 2K-FA (50v FET's ?)     =  32/39/49/60

TenTec Centurion (2x 3-500z's)     =  38/50/58/58
TenTec Titan II (4cx1600b)           =  29/31/35/50

THL 1.2kFX (50v FET's ?)              =  36/39/50/65  (up to 2:1 SWR)
THL 1.5kFX (50v FET's ?)              =  36/39/50/57   "        "

Hardrock-50 (50-watt QRP amp)   =  38/39/38/46




4)  General Notes (that are "generally" true) Smiley :
---- Typically most tube amps will load fine into SWR's of up to 2:1, and many will load fine into SWR's of up to 3:1 even at max power....but you will need to make sure you are actually "tuned" correctly....
Solid-state amps are much "touchier", and most that do not have tuners built-in,  will require external tuners to be used throughout the bands....(especially on 40m and 80m, and even on 20m and 15m for many antennas)

---- Another observation is that the amps that are driven hard to make their rated (or typical) outputs, suffer with poorer IMD results...


---- And, three notes that are connected....
- As can be seen, most of the triode amps, certainly all the legal limit triode amps, are very clean and unless overdriven or badly mis-tuned would never cause splatter themselves....

- Also, the tetrode amps (which are generally worse than the triodes) are not too bad compared to the solid-state amps...(but many have mentioned that they can be touchy-tuning and/or unless CPU-protected may be more prone to overdriving...Huh

- Amp design (both the RF tank circuit and power supply) DO have a good deal of influence on its IMD products....as can be easily seen, amps with better design / more critical design, generally produce lower IMD products than other amps using the same tubes/devices....
So, you DO (mostly) get what you pay for!!!




I suppose there is more, but I've gotta' go to Christmas dinner....so that's all for now!


Merry Christmas and Happy Holidays to all!!!!

73, 
John,  KA4WJA


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KH6AQ
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« Reply #1 on: December 25, 2014, 12:19:44 PM »

Listed are the ARRL IMD test results for several currently manufactured amplifiers. Included are the Acom 1500 tube amp, the Ameritron ALS-1300 SS amp, the Icom IC-PW1 SS amp, the Yaesu VL-1000 SS amp, the Ten Tec Centurion tube amp, the Elecraft KPA500 SS amp.

Listed by 3rd order from worst to best: Yaesu, Acom, Elecraft, Icom, Ten Tec, Ameritron. Best is ss and tube, worst is solid state.
Listed by 5th order from worst to best: Acom, Icom, Yaesu, Ameritron, Ten Tec, Elecraft. Best is solid state, worst is tube.
Listed by 7th order from worst to best: Elecraft, Yaesu, Acom, Ameritron, Ten Tec, Icom. Best is solid state, worst is solid state.
Listed by 9th order from worst to best: Ameritron, Elecraft, Acom, Ten Tec, Yaesu, Icom. Best is solid state, worst is solid state.

The best for 7th and 9th order is the Icom solid state amp. The best for 3rd and 5th order is the Ten Tec tube amp.

       tube           ss            ss          ss           tube          ss                              
      Acom      Ameritron     Icom       Yaesu      Ten Tec    Elecraft     spread        best                    worst
       best    worst
3rd, -33 dBc    -38 dBc    -36 dBc    -30 dBc    -38 dBc     -34 dBc       8 dB     Ameritron/Ten Tec      Acom             ss/tube   tube
5th, -39 dBc    -43 dBc    -41 dBc    -41 dBc    -50 dBc     -53 dBc     12 dB     Ten Tec                     Icom/Yaesu     tube       ss
7th, -50 dBc    -54 dBc    -61 dBc    -46 dBc    -58 dBc     -46 dBc     15 dB     Icom                         Elecraft           ss          ss
9th, -55 dBc    -49 dBc    -74 dBc    -60 dBc    -58 dBc     -54 dBc     25 dB     Icom                         Ameritron        ss          ss

From this list if one wants the best higher order IMD performance solid state is the answer.
« Last Edit: December 25, 2014, 12:31:09 PM by WX7G » Logged
KA4WJA
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« Reply #2 on: December 25, 2014, 01:02:27 PM »

I did list the Acom 1500, the Ameritron ALS-1300, and the Tentec Centurion....and please understand that it was not my intention to draw conclusions, especially "knee-jerk conclusions", and I specifically did NOT break the list up as "tube" vs. "solid-state", as the other variables that effect things (such as tank circuit design and construction, power supply, etc.) are beyond the capabilities of an on-line discussion board ...please read the above posting again...


But yes in my haste to eat dinner, I forgot to report the Icom, Yaesu, and Elecraft 500-watt amp....(sorry about that!)

But, Dave, as in the other thread you are misrepresenting this, as you are using db (PEP) numbers, but listing then as "dbc"...thereby giving those numbers a 6db advantage...


Icom PW-1 (50v FET's)                    =  36/41/60/60 db(PEP) not dbc

Yaesu VL-1000 Quadra (50v FET's)   =  32/44/49/59 db(PEP) not dbc


Elecraft KPA-500 (500-watt amp)     =  34/53/46/54 db (PEP) not dbc

            
Listed are the ARRL IMD test results for several currently manufactured amplifiers. Included are the Acom 1500 tube amp, the Ameritron ALS-1300 SS amp, the Icom IC-PW1 SS amp, the Yaesu VL-1000 SS amp, the Ten Tec Centurion tube amp, the Elecraft KPA500 SS amp.


From this list if one wants the best higher order IMD performance solid state is the answer.
And, please forgive me, but...
But, I think you need to look closer at the numbers...


Again, forgive me for being blunt....but I think you are misunderstanding things here...
It was NOT my intention to draw conclusions, especially since there ARE variables (such as amp RF Tank design, power supply, etc.) which effct things greatly....but since you are drawing some erroneous ones, perhaps you could use just a short list, broken-down, to compare??

Please compare the amps again...just picking a dozen from the list at random...

Tube:
Alpha 9500 (1x 8877/3cx1500a7) =  45/49/56/57  (at up to 3:1 SWR)
Alpha 87a (2x 3cx800's)               =  50/46/65/62   "            "
Acom 1000 (Gu74b/4cx800)         =  44/55/55/60   "            "
Ameritron AL-82 (2x 3-500z's)      =  38/54/53/53  (typ up to 3:1 SWR)
Ameritron AL-811 (3x 811a's)       =  40/46/56/58
Commander HF-2500 (2x 3cx800's)=  53/56/58/60


Solid-State:
Ameritron ALS-600 (50v FET's)      =  30/40/42/48  (up to 2:1 SWR)
Ameritron ALS-1300 (50v FET's)    =  38/43/54/49  (up to 2:1 SWR)
SPE Expert 1K-FA (50v FET's ?)     =  42/43/49/56  (built-in autotuners, handle
SPE Expert 2K-FA (50v FET's ?)     =  32/39/49/60
THL 1.2kFX (50v FET's ?)              =  36/39/50/65  (up to 2:1 SWR)
THL 1.5kFX (50v FET's ?)              =  36/39/50/57   "        "


That's a full dozen amps, 6 tube and 6 SS, from 6 different manufacturers....all either current production, or currently popular on-the-air and easily available used....
IF...
If, you feel it necessary to use a small sample, please use these and compare...
(I think your conclusions will change...Smiley )




Merry Christmas and Happy Holidays!

73,
John,  KA4WJA
« Last Edit: December 25, 2014, 01:08:55 PM by KA4WJA » Logged
DL8OV
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« Reply #3 on: December 25, 2014, 01:26:20 PM »

Alpha 87a (2x 3cx800's)               =    50/46/65/62
Commander HF-2500 (2x 3cx800's)=  53/56/58/60

I knew that tube power amplifiers were good but I didn't realize how good, those figures are amazing.

Peter DL8OV
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W1BR
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« Reply #4 on: December 25, 2014, 02:59:42 PM »

These results are odd, can anyone explain why?

Solid-State:
Ameritron ALS-600 (50v FET's)      =  30/40/42/48  (up to 2:1 SWR)
Ameritron ALS-1300 (50v FET's)    =  38/43/54/49  (up to 2:1 SWR)
 

Isn't the 1300 two ALS-600 in the same box with a combiner?

Pete
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KA4WJA
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« Reply #5 on: December 25, 2014, 03:31:46 PM »

Pete,
If it were just that the 1300 was only two 600's combined, yes logic says that there shouldn't be this much difference....but, I suspect that there is more to the 1300 than "just two 600's"....and of course, it's likely that the amp modules and combiners are designed/constructed differently as well as the power supplies...and that, in the real-world, the 1300 is not "just two 600's, in one box"??
These results are odd, can anyone explain why?

Solid-State:
Ameritron ALS-600 (50v FET's)      =  30/40/42/48  (up to 2:1 SWR)
Ameritron ALS-1300 (50v FET's)    =  38/43/54/49  (up to 2:1 SWR)
 

Isn't the 1300 two ALS-600 in the same box with a combiner?

BTW, just fyi....these figures are directly from the ARRL Product reviews...
Ameritron ALS-600s,  from March 2005 QST...
Ameritron ALS-1300,  from September 2011 QST...

{and the original ALS-600 w/liner supply, from August 2001 QST....shows even different numbers.... 37/40/57/58....}


Again, this and all the above data, DOES show variables in RF output circuitry and power supply design AND construction, that eliminates easy/knee-jerk conclusions....
Which is why I posted all this, AND cautioned drawing quick conclusions....




Merry Christmas and Happy Holidays!!!


73,
John,  KA4WJA
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KA4WJA
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« Reply #6 on: December 25, 2014, 04:30:53 PM »

Just a couple minor comments, some "expanded test results", and ARRL tests results on "other" amps...

1)  Looking at the ARRL "expanded test results", which were only done for the Alpha 91,  Ameritron AL-800H,  and the QRO HF-2500dx.....shows how using lower drive power / lower output power, can effect the amp's IMD products....

I wish I could get the images from all of these tests to post....but at least the numbers are here!!!

Alpha 91  (2x Gu74b/4cx800's)     =  45/49/57/64   (basic report)
Alpha 91  (2x Gu74b/4cx800's)     =  47/50/56/63 (at 1500 watts, on 20m)  
Alpha 91  (2x Gu74b/4cx800's)     =  42/65/65/60 (at 1000 watts, on 20m)
Alpha 91  (2x Gu74b/4cx800's)     =  42/57/64/63 (at 750 watts, on 20m)


Ameritron AL-800H (2x 3cx800's)  =  49/55/63/63   (basic report)
Ameritron AL-800H (2x 3cx800's)  =  47/55/58/63 (at 1500 watts, on 20m)
Ameritron AL-800H (2x 3cx800's)  =  47/60/60/63 (at 1000 watts, on 20m)
Ameritron AL-800H (2x 3cx800's)  =  49/59/57/62 (at 750 watts, on 20m)  


QRO HF2500dx (2x Gu74b/4cx800's)=  43/40/57/60  (basic report)
QRO HF2500dx (2x Gu74b/4cx800's)=  43/40/58/60  (at 1500 watts, on 20m)
QRO HF2500dx (2x Gu74b/4cx800's)=  43/40/60/60  (at 1000 watts, on 20m)
QRO HF2500dx (2x Gu74b/4cx800's)=  40/48/63/62  (at 750 watts, on 20m)




2)  It was just HF amps that I was looking at (and/or those also covering 6m), but there aren't any ARRL test results available for the newer single (or dual) LDMOS device amps on HF....but there ARE results for the 2m/144mhz M-square LDMOS amp, and it ain't too pretty....and according to some inside sources (the RF/EMC lab testing the amps for FCC certification), they had trouble getting the amps FCC certified...

M-squared M2-1k2 (single LDMOSFET) at 144mhz =  26/43/43/52




3)  There are also a few other amps that the ARRL has reviewed, but NOT published IMD data for...such as the Yaesu FL-7000 (which just has the statement that they was below 25db below PEP....no kidding, the ARRL thinks that's acceptable??)

And, others which are not really "hi-power" amps, such as the SGC-500, 500-watt mobile amp....the Elecraft KPA-100, 100-watt amp for QRP radios....

SGC-500 (8x 12volt bipolar, mobile amp)  =  28/48/49/53

Elecraft KPA-100 (2x 12volt bipolar)          =  26/40/41/51

Elecraft KPXA-100 (12vdc)                        =  32/34/42/52



4)  And, even though I'm usually a fan of triodes, the 4cx1500b is an exception (and one great tube!)....
So, when the ARRL gets around to testing the Alpha 8410 (with its pair of 4cx1500b's), I suspect that they will find one of cleanest amps sold today!!

{And, with the incredibly low drive necessary for the 4cx1500b, I suspect that some will do a little "mod", and get close to 1500 watts out, with just QRP drive power....}




Merry Christmas and Happy Holidays!!!


73,
John,  KA4WJA

« Last Edit: December 25, 2014, 04:56:11 PM by KA4WJA » Logged
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« Reply #7 on: December 25, 2014, 07:03:58 PM »

Just a couple minor comments, some "expanded test results", and ARRL tests results on "other" amps...

1)  Looking at the ARRL "expanded test results", which were only done for the Alpha 91,  Ameritron AL-800H,  and the QRO HF-2500dx.....shows how using lower drive power / lower output power, can effect the amp's IMD products....

I wish I could get the images from all of these tests to post....but at least the numbers are here!!!

Alpha 91  (2x Gu74b/4cx800's)     =  45/49/57/64   (basic report)
Alpha 91  (2x Gu74b/4cx800's)     =  47/50/56/63 (at 1500 watts, on 20m)  
Alpha 91  (2x Gu74b/4cx800's)     =  42/65/65/60 (at 1000 watts, on 20m)
Alpha 91  (2x Gu74b/4cx800's)     =  42/57/64/63 (at 750 watts, on 20m)


Ameritron AL-800H (2x 3cx800's)  =  49/55/63/63   (basic report)
Ameritron AL-800H (2x 3cx800's)  =  47/55/58/63 (at 1500 watts, on 20m)
Ameritron AL-800H (2x 3cx800's)  =  47/60/60/63 (at 1000 watts, on 20m)
Ameritron AL-800H (2x 3cx800's)  =  49/59/57/62 (at 750 watts, on 20m)  


QRO HF2500dx (2x Gu74b/4cx800's)=  43/40/57/60  (basic report)
QRO HF2500dx (2x Gu74b/4cx800's)=  43/40/58/60  (at 1500 watts, on 20m)
QRO HF2500dx (2x Gu74b/4cx800's)=  43/40/60/60  (at 1000 watts, on 20m)
QRO HF2500dx (2x Gu74b/4cx800's)=  40/48/63/62  (at 750 watts, on 20m)




2)  It was just HF amps that I was looking at (and/or those also covering 6m), but there aren't any ARRL test results available for the newer single (or dual) LDMOS device amps on HF....but there ARE results for the 2m/144mhz M-square LDMOS amp, and it ain't too pretty....and according to some inside sources (the RF/EMC lab testing the amps for FCC certification), they had trouble getting the amps FCC certified...

M-squared M2-1k2 (single LDMOSFET) at 144mhz =  26/43/43/52




3)  There are also a few other amps that the ARRL has reviewed, but NOT published IMD data for...such as the Yaesu FL-7000 (which just has the statement that they was below 25db below PEP....no kidding, the ARRL thinks that's acceptable??)

And, others which are not really "hi-power" amps, such as the SGC-500, 500-watt mobile amp....the Elecraft KPA-100, 100-watt amp for QRP radios....

SGC-500 (8x 12volt bipolar, mobile amp)  =  28/48/49/53

Elecraft KPA-100 (2x 12volt bipolar)          =  26/40/41/51

Elecraft KPXA-100 (12vdc)                        =  32/34/42/52



4)  And, even though I'm usually a fan of triodes, the 4cx1500b is an exception (and one great tube!)....
So, when the ARRL gets around to testing the Alpha 8410 (with its pair of 4cx1500b's), I suspect that they will find one of cleanest amps sold today!!

{And, with the incredibly low drive necessary for the 4cx1500b, I suspect that some will do a little "mod", and get close to 1500 watts out, with just QRP drive power....}




Merry Christmas and Happy Holidays!!!


73,
John,  KA4WJA



It may also illustrate variables between the various test sessions as well. I would not make a decision based on singular data points for each model. 

Pete
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« Reply #8 on: December 26, 2014, 12:14:22 AM »

My amp is better than your amp
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« Reply #9 on: December 26, 2014, 03:02:54 AM »

And in the case of Tetrodes the final IMD figure is several orders of magnitude worst because Tetrodes are inherently the worst splattering tubes  because tetrodes dont
tolerate grid current  very well.  When we throw into the mix the typical transceiver power spikes, ALC overshoot, other crud from the transceivers, and the poorly designed EBS systems on all commercial ham tetrode amplifiers, the final  IMD picture is far from healthy.

Another question is why stop reporting IMD figures at the 9th order? While it might be convenient for the ARRL's test reports,  a more complete picture of any amplifiers performance is how quickly the IMD products from the 11th order and greater drop. Many well designed tubes amplifiers the IMD can fast disappear above the 9th order especially when the tube is a linear SSB tube. This is not  the case for solid state amps, and all IMD products should be  reported. Many solid state amps the  actual IMD above the 9th order actually get worst and this can be the source of annoying buckshots or spits and spats that we hear on the band.

Any station wanting to  do an IMD evaluation of their station  the best test procedure is to use a dynamic  test into a dummy load while using a SDR receiver as a spectrum analyzer.
The  poor design flaws of radios and amplifiers are always revealed, and the reality is never what your ham buddies say it is.

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« Reply #10 on: December 26, 2014, 05:34:02 PM »

One of my concerns with using ARRL data and most other sources is that these tests are done over such vast periods of time that it begs the question how reliable are the numbers, given in some cases the small differences.  Some of these Amps where tested over 20 years ago and other just a year ago and the sample size in all cases is just one unit.  I am pretty sure the test equipment changed during that period and It would also be nice if more than one unit had been tested.

73s
Rob

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KA4WJA
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« Reply #11 on: December 26, 2014, 06:48:37 PM »

Rob,
I agree with your concerns here...especially being "a sample of only one" is tested!!

But, unfortunately the ARRL Product Test Reports are the only real numbers we have to work with, where we have actual "tested" numbers, from many different products...
One of my concerns with using ARRL data and most other sources is that these tests are done over such vast periods of time that it begs the question how reliable are the numbers, given in some cases the small differences.  Some of these Amps where tested over 20 years ago and other just a year ago and the sample size in all cases is just one unit.  I am pretty sure the test equipment changed during that period and It would also be nice if more than one unit had been tested.
I've seen an occasional test report or scans from some hams.....such as the transceiver scans that Rob Sherwood, NC0B, uses in his presentations...

Here is a 2-tone IMD test, of a Alpha 77 at about 2000+ watts PEP, driven by an FT-1000 (in Class A)...(courtesy of Rob, NC0B)


And, for comparison, here is the FT-1000 alone, at 75 watts, in Class A...(courtesy of Rob, NC0B)




And, I've seen FCC test reports from type certified gear (maritime/commercial, non-ham gear), but nowhere have I seen the breadth of gear tested than from the ARRL...


So, while I think the "editorial" policies and rather lax comments by even the technical writers, of the ARRL to be rather lacking.....I do have faith that these 2-tone IMD tests were preformed the same over the years, and that their equipment was well cal'ed, etc....
(and I especially like that they usually publish the spectral scans in their pdf files)




73,

John, KA4WJA
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KA4WJA
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« Reply #12 on: December 26, 2014, 07:29:29 PM »

Zenki,
I'm usually on your side...and I'm also not usually a big fan of tetrode amps....
And, YES....I also wish to see scans for ALL IMD products, out past 11th and 13th orders....(but, we have what we have, and we can only compare what we have!!)

But...

But, would please show some numbers here...
I mean if we wish to educate folks, opinions don't work....we need some facts....and most will need to see the actual numbers from actual amps...


Yes, the data sheet from the Gu74b/4cx800 shows rather disappointing 3rd and 5th order specs....
GU74b/4cx800    =  -34 / -34  (-28dbc/-28dbc)

http://www.qro-parts.com/images/pdf_files/GU74B.pdf
http://frank.pocnet.net/sheets/018/g/GU74B.pdf


But, the 4cx1500b is a rather fine tube!!!  (and is specifically designed for low distortion products...)
4cx1500b           =  -49 / -53  (-43dbc/-47dbc)

http://www.tubecollectors.org/eimac/archives/4cx1500b(66).pdf
http://www.g8wrb.org/data/Eimac/4CX1500B.pdf


And, while the ARRL Test reports do show the triode amps to be cleaner, the results from some tetrode amps aren't too bad, and certainly MUCH better than the SS amps...

Here are a half-dozen legal-limit amps (3 triode and 3 tetrode), and one each mid-power amps...

Triode amps:
Legal limit:
Alpha 9500 (1x 8877/3cx1500a7) =  45/49/56/57  
Alpha 87a (2x 3cx800's)               =  50/46/65/62  
Ameritron AL-800H (2x 3cx800's)  =  49/55/63/63

1000watt:
Commander HF-1250 (3cx800)      =  46/44/52/57


Tetrode amps:
Legal limit:
Alpha 91  (2x Gu74b/4cx800's)     =  45/49/57/64
Alpha 8100 (2x Gu74b/4cx800's)  =  52/48/53/61
OM2500A (Gu84b/4cx2500a)         =  43/44/60/56

1000watt:
Acom 1000 (Gu74b/4cx800)         =  44/55/55/60


Yes, I'd take a pair of 3-500z's or an 8877, any day over a pair of Gu74b's....or even better a pair of 8877's, for lots of reasons!!! (Good IMD performance being just one of them)....driven with a commercial exciter or Class A exciter...

But, can you show me the "orders of magnitude" difference?


When you rail about the horror of using tetrodes, many here want to see the numbers....would you please post some test results from tetrode amps that support your comments here...
And, please let's not get into a "horrible transceiver" discussion (power spikes, ALC-overshoot, and all the exciter's horrible IMD products), as we've discussed this in great detail before (and we are in agreement on all of that)....
http://www.eham.net/ehamforum/smf/index.php/topic,97093.0.html

So, dealing with the topic at hand...HF amps....please provide some specific test result numbers...perhaps you have some dynamic IMD test results???  
Or maybe you've got test results using "white noise"Huh  Or, are there other tetrode amps that are being sold these days, that I have not posted the ARRL test results of???

And in the case of Tetrodes the final IMD figure is several orders of magnitude worst because Tetrodes are inherently the worst splattering tubes  because tetrodes don't tolerate grid current  very well.




And, while I do agree with you here..
 Many well designed tubes amplifiers the IMD can fast disappear above the 9th order especially when the tube is a linear SSB tube. This is not  the case for solid state amps, and all IMD products should be  reported.
I was attempting to post actual test results and not state absolute conclusions....at least not without supporting data....




 
Zenki, would you do us the favor of posting your test results....'cause I don't have an SDR, nor lost of amps on the shelf to test...
Any station wanting to  do an IMD evaluation of their station  the best test procedure is to use a dynamic  test into a dummy load while using a SDR receiver as a spectrum analyzer.
The  poor design flaws of radios and amplifiers are always revealed, and the reality is never what your ham buddies say it is.
Please show us...



Happy New Year to all!!

73,

John,  KA4WJA
« Last Edit: December 26, 2014, 07:33:15 PM by KA4WJA » Logged
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« Reply #13 on: December 26, 2014, 08:14:40 PM »

Alpha 8100 (2x Gu74b/4cx800's)  =  52/48/53/61  (at up to 3:1 SWR)

Looks pretty damn good for a pair of tetrodes!!! 
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K6AER
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« Reply #14 on: December 26, 2014, 09:50:23 PM »

Before you get to far down the list there are some corrections to the RF Concepts list.

The early 8410 uses a pair of 4CX1000A's now they use a pair of 4CX1500B's.

The 8100 amplifier was very limited production. Few were built.

They make a 8406 6 meter amplifier that uses a 4CX1500B but I did not see that listed.

Here is the most important specification not listed...what was the power out when the tests were made?
« Last Edit: October 19, 2016, 08:19:47 PM by K6AER » Logged
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