Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: Prev 1 [2] 3 4 5 6 7 ... 9 Next   Go Down
  Print  
Author Topic: Hallicrafters SX-115 selectivity design eror  (Read 44193 times)
K9AXN
Member

Posts: 442


WWW

Ignore
« Reply #15 on: March 20, 2015, 08:53:19 AM »

Good morning Tom,

You don't know anything about me.  Take a moment and look at www.k9axn.com then you can decide what my affiliation is with Hallicfrafters engineers.  I was one of the people they worked with to test some of the SR-400, SR-400A, and SR-2000 engineering changes etc.  My opinion regarding the Hallicrafters designers is top of the line and the most creative of the times.  There were non better and that includes Collins.  I make mistakes and so to do other people in the design field.

There is not one statement that I made that is not 100% accurate.

First I will point you to the selectivity charts.  How do you suppose the center of the bandpasses moved away from the carrier and what do you suppose caused the move??  If you insert a capacitor in series with another, will the capacity increase or decrease?  Now get your calculator out and redo the math.  First I will ask you the combined capacity for each selectivity setting.  OK what is it?  Now calculate the resonant point.  Voila, the resonant point has moved the band center away from the carrier to accommodate the widened pass band created by coupling and the added resistors will reduce the Q to reduce the over coupling to critical.  The distance the center moved is as I stated.  Please reread the numbers.

Have you aligned an SX-115 or SX101?  Having an SX-101  --- yes you have.  First thing done on the 50.75 I.F. is to align the system at 50.75 using the .5Kc position.  That uses none of the caps or resistors on the selectivity switch.  However, if you reexamine the schematic there is a .02uf Z5U -20+80 capacitor in series with the 390's when in the .5Kc position.  Do you understand the -20+80 meaning?  That circuit is never shorted together in the second 50Kc tuned circuit.

Revisit the circuit design.  The two 390uf caps share the capacity in the selectivity circuit.  They're essentially in parallel but series with the selectivity caps and the resistors in series with the secondary winding.  I would encourage you to recalculate your supposition.  I to make frequent miscalculations.  
  
The capacitors that were used in those circuits are virtually condemned in every engineering research paper ever written.  If you should find one that contradicts anything that I have stated please bring it to my attention.  What I stated was correct!!!  The Hallicrafters engineers were cognizant of the frailties of the Ceramic Z5U capacitor and I believe one of the most careful design groups selecting components.  If you read the statement, I said the SX-115 is the ONLY radio using the 50Kc I.F. made by Hallicrafters to use the Z5U in the Selectivity circuits.  I never said it was negligence, more likely an oversight.

Judging from your tone, I wonder if you responded to this as a proxy for the belligerent one?  I sincerely hope not.

If not my apologies.

Have a super day and yes I consider you a friend in that you feel strongly about the great mark that the Hallicrafters people made on the era of radio.

Kindest regards Jim K9AXN  
 
« Last Edit: May 11, 2015, 08:03:07 AM by K9AXN » Logged
W8JI
Member

Posts: 9748


WWW

Ignore
« Reply #16 on: March 20, 2015, 09:04:36 AM »

But, the bumble caps used in the earlier SX-101 series was a magnitude better than Z5U dielectric caps.  They had better choices available.  Z5U is fine for bypassing, but I won't want to see it used in a critical coupling application.

Sometimes manufacturers cut a few corners to save a few pennies. It isn't always about using the best available parts for an application.

Pete

It isn't critical, and more important it doesn't even work the way the outline at the start of this thread describes.

The particular capacitors do not have to be exceptionally temperature stable.

My description was just a really rough overview, but if we are going to get a "feeling" for how the system works we have to understand the basic function of the components.

The capacitors determine mutual coupling. They are switched so they are open (maximum k and maximum bandwidth), or progressively decrease in shunt reactance until finally a "short" appears. At the point where it is a short, the 2.2 pF sets the tuned circuit coupling.

The actually system is much more complex than this, but this is the simplest operational description that explains the system.

If a capacitor drifts what we might assume is significant in value, the effect on the system is in fact relatively small. They are not tuning capacitors, they do not "shift the frequency" except as a small unintended effect. That shift is primarily in the upper passband frequency limit. There are three that are connected in various combinations. The 5,3,2,1, and .5 kHz sequence is:

5kHz  = 4700 pF
3 kHz  = 10,000 pF
2kHz = 14,700 pF
1 kHz = 24,700 pF
.5 kHz = short  

A normal drift from using non-special parts obviously had minimal effect. The frequency is primarily determined by the 390 pF caps. As a matter of fact, if we went from 10,000 pF to 24,700 pF for the bandwidth determining capacitor the center frequency of a 500 Hz wide 50.849 kHz IF would move from 51.229 to 51.756 kHz.  It moves ~500 Hz center for a change from 1kHz to 3 kHz bandwidth and the passband still overlaps other stages.

There is no amount of drift in the bandwidth capacitor that pulls the IF out of passband.

The bandwidth determining capacitor is not critical for normal drift of a standard capacitor, and that is why they used what they used. If the capacitor goes bad and goes severely off, like leaky or shorted, that is another issue.

73 Tom



Logged
W8JI
Member

Posts: 9748


WWW

Ignore
« Reply #17 on: March 20, 2015, 09:29:15 AM »

Good morning Tom,

<snip>

Kindest regards Jim K9AXN  
 

Jim,

This is nothing personal. The components Hallicrafters picked were 100% suitable for the application. It was not an "engineering mistake". I have no problem improving old radios, but we have to be reasonably accurate in understanding how the circuit works, or we can't accurately decide why the parts they used were used.

In this case, the numbers I gave were correct. I gave an example of a single stage assuming 100k ohms source and load impedance and the approximate values of the Hallicrafters parts:

Quote
5kHz  = 4700 pF
3 kHz  = 10,000 pF
2kHz = 14,700 pF
1 kHz = 24,700 pF
.5 kHz = short  

A normal drift from using non-special parts obviously has minimal effect. The frequency is primarily determined by the 390 pF caps. As a matter of fact, if we went from 10,000 pF to 24,700 pF for the bandwidth determining capacitor the center frequency of a 500 Hz wide 50.849 kHz IF would move from 51.229 to 51.756 kHz.  It moves ~500 Hz center for a change from 1kHz to 3 kHz bandwidth and the passband still overlaps other stages.

This is the reason they used the type of components they used. I'm certain we would all like the 50-100 year old radios we have to use parts from the last 20 years, but they were built in the 1950's and earlier. There is no reason to use a precision capacitor or a temperature stable capacitor for the bandwidth capacitors, because the primary frequency determination is in the stability of the 390 pF caps and the inductors.  

The circuity has a 390 pF "resonating" capacitor from each inductor in series with a selectable .0047,   0.01,  .0147, and .0247 capacitance. The dominant reactance at 50 kHz is in the inductor and the 390 pF (plus circuit strays). The large capacitors, which have relatively low reactance compared to the 390 pF capacitors, primarily set bandwidth by changing coupling.

If that circuit were designed today, there would be little reason to use an NP0 TC capacitor. Why then are we calling it a mistake when temperature stable caps in the 10,000 pF range were terribly expensive in 1950? What I see is a 2015 analysis mistake, not a 1950 mistake.  Smiley

They are 50 year old parts. If they have gone bad, change them. If you want to be overly picky, use C0G's or something. It won't work significantly different than a standard Z5U, however it might make us feel.  The change from 2kHz bandwidth to 1kHz BW is 10,000 pF. I doubt a .01uF capacitor is going to drift anything remotely close to .005 uF.

73 Tom
« Last Edit: March 20, 2015, 09:32:32 AM by W8JI » Logged
G3RZP
Member

Posts: 1284




Ignore
« Reply #18 on: March 20, 2015, 10:03:12 AM »

But what about the change in k with tolerance, temperature and age?? Of course, the other 'slight' complication is that one has to assume that the coil Q is the same as 50 odd years ago for many calculations to make sense. For bottom capacity coupling - where one uses large value capacitors - then

k =  (C1C2)0.5/Cc

where C1, C2 are the tuning capacitors and Cc is the coupling capacitor.

So a 20% variation in coupling capacitance means a 20% variation in k, and if one wanted critical coupling where kQ = 1, you could be kQ = 1.2 with the -3dB point on one coupled pair at where the -6dB point should be, or you could have kQ = 0.8 where the -6dB point would be about -8dB.

So from a tolerance viewpoint, stable close tolerance capacitors would be a best bet, and even in the late 1950s, high Q and reasonably stable, close tolerance polystyrene film caps were available. In the sorts of values that would be wanted, they were made with multiple wires to the foils to keep Q up, and the temperature stability and repeatability was enough for stable filters in FDMA telephone systems when used with suitable ferrites - which is where the fallacy has come from in some circles that polystyrene capacitors and ferrite cored coils always compensate each other.

There are a lot of designs out there where coupling is by means of top capacity coupling: that, unless Q is very low, ends up with small capacitors with a necessarily high tolerance and thus an ill defined value of k. But that is very popular coupling method amongst amateurs.....

Of course, where inductors are variable, then using capacitive coupling helps keep kQ constant over the tuning range, and vice versa when the tuning is by variable capacity.
Logged
K9AXN
Member

Posts: 442


WWW

Ignore
« Reply #19 on: March 20, 2015, 10:11:18 AM »

Good morning again Tom,

I didn't take it personal and am happy to engage in technical discussion; and respect you for responding.  

The facts and numbers are not negotiable.  Your calculations are simply incorrect.  What I stated about the function of those capacitors and resistors is absolutely correct.  The band centers are also correct.  Please review the Hallicrafters published band pass locations.  Those charts are correct and the measurements that I made match the charts.  If you should have sweep capabilities just sweep it and it will be obvious.  Please take a moment and rethink your supposition.  

I will ask two questions:

The parts that they picked were an absurd choice for that application.  What research paper did you find that suggests the use of Class 3 ceramic capacitors in any tuned circuit --- ever, even 50 years ago?

Why did the Hallicrafters folks use paper then film caps in every other 50Kc system?  Even paper is legions better that Class 3 ceramic, that is if they didn't become dangerous with age.  The SX-117 used Film caps. It was built during the same period for those who could not afford the flagship SX-115.  I can unequivocally state that the SX-115 in every other respect is a superb radio.

Case closed for me.  If you want your selectivity circuits to work properly, replace those caps with Polypropylene.  This is not a negotiable notion; simply good design practice and yes the difference is distinguishable.

Have a super day --- Kindest regards Jim

  
Logged
W8JI
Member

Posts: 9748


WWW

Ignore
« Reply #20 on: March 20, 2015, 11:46:13 AM »

But what about the change in k with tolerance, temperature and age?? Of course, the other 'slight' complication is that one has to assume that the coil Q is the same as 50 odd years ago for many calculations to make sense. For bottom capacity coupling - where one uses large value capacitors - then

k =  (C1C2)0.5/Cc

where C1, C2 are the tuning capacitors and Cc is the coupling capacitor.

So a 20% variation in coupling capacitance means a 20% variation in k, and if one wanted critical coupling where kQ = 1, you could be kQ = 1.2 with the -3dB point on one coupled pair at where the -6dB point should be, or you could have kQ = 0.8 where the -6dB point would be about -8dB.


Peter,

Certainly a better capacitor would be more stable for stability of coupling and selectivity, but these receivers have a relatively poor shape factor anyway. I didn't get into a problem with coupling capacitor stability even with ~100 Hz bandwidths and shape factors of 3 or 4, which was about the limit of what I could do with 15 or 20 inductors.

The actual filter I used was a current carrier filter from a utility company. I moved it to the IF frequency by changing capacitors across the inductors, and increased the bandwidth by increasing coupling. The tuning capacitors, of course, had to be stable silver micas. The coupling capacitors were perfectly fine using standard disc capacitors at temperatures encountered in the box.

The important points here are:

1.) the large value capacitors do not move the IF frequency significantly in comparison to IF bandwidth

2.) the 390 pF capacitors, along with the inductors, are the primary frequency determining parts and are critical for stability 

3.) the 2.2 pF and the quality of the "short" at the switch set the 500Hz bandwidth. All the capacitors do is increases the coupling factor from that minimum point

4.) the effect of decreasing Cbw is to narrow bandwidth. The lower frequency -6dB point of each stage stays almost constant, while the center frequency shifts upward. The upper frequency -6dB shifts upwards the most. 

5.) because of circuit loading and limited inductor Q, none of which is known, we can be sure the shift is less than a perfect circuit. A perfect circuit doesn't appear to be a problem with good normal non-special capacitors.

It doesn't seem like Hallicrafters made any engineering mistake. They used the parts they had available 50-60 years ago.

It's unfortunate a few 50 year old parts are frequently bad today, but that doesn't mean someone made a mistake. It also doesn't mean we have to overkill the circuit. I'd probably use an X7R or something tighter than a Z5U, but most Z5U's are far better than spec and would likely not be noticeable. A C0G or NP0 would be not be any improvement.

These things have pretty wide skirts, even when perfect. 

We should not confuse 50 year old bad parts with bad engineering.

73 Tom
Logged
G3RZP
Member

Posts: 1284




Ignore
« Reply #21 on: March 20, 2015, 12:18:36 PM »

Tom,

I can't agree. To use capacitors which give a wide tolerance on kQ when that defines selectivity is not good practice, although I suppose for an amateur receiver, it's not so important. For marine receivers subject to Type Approval and definite requirements on selectivity (back in the days when ships had radio officers and used Morse!), it would not have done at all, and it was usual to use silver mica for coupling and tuning capacitors, as well checking every IF coil for inductance, tuning range and Q.  Similarly, professional receivers for non-maritime applications used close tolerance capacitors in switched selectivity IF stages.

My father's HQ170 had ceramic coupling caps, and the IF responses never quite matched up with their curves! Eddystone in the UK did a number of receivers where the coupling was changed by moving the relative position of the IF coils, similar to the method used in the BC453. That at least has the advantage that the coupled circuit far off resonance still has a monotonic response, while other coupling methods degenerate into either a low pass or a high pass response, albeit with high attenuation.
Logged
W8JI
Member

Posts: 9748


WWW

Ignore
« Reply #22 on: March 20, 2015, 12:59:06 PM »

The selectivity at best is already so wide, the caps matter very little.
Logged
K9AXN
Member

Posts: 442


WWW

Ignore
« Reply #23 on: March 20, 2015, 05:27:56 PM »

Hi Tom,

You say the selectivity is lousy.  What kind of capacitors did you use in your radio?

You also say those large capacitors have nothing to do with the resonant point.

Please get your calculator out and do a simple set of calculations that should help to understand the issue.

On the SX-115 the second 50Kc tuned circuit you will find C90, C91, and C92.  You must look at C86 also.  You say why because it's only a bypass capacitor.  It is a direct part of that resonant circuit.  Careful, there are many many (Bypass capacitors that participate in resonant circuits and also bypass RF to ground).

Calculate the resonant frequency of the switch in the .5Kc position.  and remember to use C86 the .02uf bypass/coupling capacitor.  The coil will be 25.7Mh.

Next calculate the resonant frequency when in the 1Kc position.  And remember the .02uf capacitor.

Next the 5Kc position.

You say those capacitors don't shift the resonant position?  Please just do the math, there is no argument here, let it speak for itself.

Now on to the Z5U class 3 capacitors behavior.

First look at the following snippet.   http://www.k9axn.com/SX-115/SX-115%20ceramic%20temperature.avi

It represents one of those Z5U's in the SX-115.  Note the starting capacity at room temperature 22 degrees C and the capacity as we heat it to 42 degrees C.  There is a pause when we reach 42 degrees.  That's the temperature behavior of the Z5U.  Think I'm doing magic and mirrors, do it yourself and note at room temperature it's at .0083 not .010 from aging.  compound that with temp shift and now we're at .0073.  Lets frost the cake and add 215 volts to the .02.  It will loose even more capacity.  the ,02 is .0165uf.  subtract at least 10% now the .02 is .015uf.

The Q at 100Kc for the Z5U is 254.  The Polypropylene Q 2900 at 100Kc and the DF for the Polypropylene 1/10 of the ceramic. 

If it makes sense to you to use ceramic Z5U caps in that circuit, don't lament the selectivity is deficient.

Do the math Tom and lets see if we can come to some conclusion.

Kindest regards Jim K9AXN
 
Logged
JS6TMW
Member

Posts: 1255




Ignore
« Reply #24 on: March 21, 2015, 06:47:52 AM »

"I'm surprised they did that--as you noted they (Z5U dilectric)  are terrible caps for temperature stability.  They make good thermistors! Even body heat shifts the value. Most of my Hallicrafters are SX-101 or earlier."

Correct - I used the effect in a miniature telemetry transmitter for ultracentrifuge rotor temperature measurement, back in 1965. Worked like a charm.
Logged
K9AXN
Member

Posts: 442


WWW

Ignore
« Reply #25 on: March 21, 2015, 02:34:59 PM »

Good afternoon Tom,

This is a truly a friendly question.  I'm and old timer that has probably forgotten more than I ever knew but you said something that bounced all around my grey matter looking for a rational solution.

You mentioned that the filter design used in the 50Kc I.F. systems, the nearest skirt is anchored 500 cycles from the carrier and the outside skirt is moved out to accommodate the wider pass band.  Would that not drag the center of the pass band along with it?  Or is it that the center is moved and the skirts are expanded?  Or are they both the same?  I got the feeling that you felt that there was some distinction between both.

Have a super evening Tom

Kindest regards Jim K9AXN

  
« Last Edit: March 21, 2015, 02:43:46 PM by K9AXN » Logged
KM1H
Member

Posts: 5289




Ignore
« Reply #26 on: March 21, 2015, 07:57:00 PM »

Tom is doing such a good job I wouldnt even have responded but Jim cant seem to help himself by taking cheap shots with no provocation, a trait Ive followed of his for many years. And yes Ive called him out several times elsewhere on various subjects so to him Im belligerent since he cant tolerate being questioned and will never back down or admit an error. Mr Smiley Perfect.

I doubt if Jim ever had a "friendly question" when in a discussion that he is losing; more like a guy with a preachers smile and a knife ready for your back. He has been trying to sell this idea for awhile and has been shopping it around. This time it hit the ground....hard.

As far as the SX-115; the claim the filter caps are Z5U's is completely bogus, at least in mine, as they are 10% "close tolerance" as called out in the manufacturers catalogs of the time. Z5U wasnt even a common term then since the EIA standards hadnt been set yet and they were simply called Hi-K by most and undefined in many cases.

My SX-115 selectivity curves are very close to the manual and the receiver is used often with a HT-32B and NCL-2000 for vintage CW, SSB and some AM and is a pleasure to use and absolutely not selectivity hampered. Halli seemed to come out with a real good radio every 10 years or so starting with the SX-28. 

The SX-117 came out a year after the SX-115, which was a very hard sell, and the claim they used film caps is more pure BS if the parts list is to be believed as they call out paper tubular and that is certainly what they looked like and leak tested in mine as I replaced with generic yellow film caps I matched to within 1% of each other. Oh and yes, surprise surprise I have both models and can easily refute a lot of nonsense here. The SX-117 is quite a bit inferior in many areas, especially selectivity, but certainly far better overall performance than most of the bottom dwelling stuff Hallicrafters were turning out in the 60's and on the way to oblivion with most of the other leaders of the past.

Both manuals even state that the selectivity steps are a matter of Q, coupling and resistance and it is obvious by examining the circuit that resonance is NOT a factor since it is an RC circuit and not LC. Halli used the same method as far back as the SX-96 and National in the NC-300, both around 1955 introductions. Halli simply copied a good idea or maybe there was some cross breeding going on(-;

Another thing Jim doesnt understand is the voltage used to determine capacitance in manufacturing is very low and likely at no more than 100 Hz at those capacitance values. Of course there will be some shift with real vacuum tube voltages which is why the Z5U +80 % variable is quoted and much higher than needed cap voltages were available to mitigate the shift if needed. The Z5U is also stated that it is not to be used in frequency determining circuits or where high tolerance is required. But that is all moot since a Hi-K cap was not used in the filter.
In addition, if you read his various pronouncements as if they were actually factual you would find that the voltage/capacitance shift charts used as examples are for 16V SMT devices, not 500-1000V disc ceramics.

I completely agree that the REAL Halli engineers knew what they were doing with the SX-115 and did it reasonably well but I still prefer my NC-300 on AM after a few mods.

Have at it Tom, Im sure most on here will enjoy it. Jim is seething with anger since he didnt expect a high level challenge to his competence...the more platitudes and sweet words he uses the more dangerous he becomes; watch your back.

I consider this whole exercise over...

Carl
Logged
K9AXN
Member

Posts: 442


WWW

Ignore
« Reply #27 on: March 22, 2015, 11:25:02 AM »

Tom, I genuinely was trying to break the ice and apologize if it sounded off tone.

Carl, I respectfully disagree with your findings.  I won't reply to every issue today but will answer every issue individually; have several grandchildren to entertain.   

First:

The SX-115 build did in fact use Ceramic Z5U 10% capacitors for the selectivity switch.

Note the photo's in the following url of the parts list and capacitors removed from an unmolested SX-115.  They unambiguously define exactly what kind of capacitors they are as well as what was defined in the build list.

http://k9axn.com/_mgxroot/page_10879.html

Carl, if the caps in your radio are not as shown in the photo, they may have been replaced already.

For all other SX-115 owners, I would suggest you check your radios for the Ceramic caps and replace them.

Note, I described the use of the capacitors as a design error because they were used in all SX-115's as defined in the parts list.  I Probably should have defined the use of those caps as a manufacturing selection error even though they were listed in the parts list.  Anyone that knows me also knows that I consider the Hallicrafters design team the premier group of the era.

Carl, the next issue is the capacitors used in the SX-117.  I believe there are a few after the SX-117 issue and will finish with the calculations to support the statements that I wrote concerning how those caps were used.

Thanks for the reply Carl and have a great day.  I genuinely wish we could have a more friendly relationship.  I guess that's one of lifes lessons.   

Kindest regards Jim K9AXN
Logged
W1BR
Member

Posts: 4189




Ignore
« Reply #28 on: March 22, 2015, 12:38:19 PM »

In the SX-101A, as far as I remember, the selectivity curve shifted center frequency as BW was changed. That assymetrical response was used too advantage for the sideband reversal system, and for CW.   I can't see where using anything other than stable capacitors would improve the situation, or yield satisfactory results.

Pete
Logged
K9AXN
Member

Posts: 442


WWW

Ignore
« Reply #29 on: March 22, 2015, 01:46:25 PM »


The SX-117 came out a year after the SX-115, which was a very hard sell, and the claim they used film caps is more pure BS if the parts list is to be believed as they call out paper tubular and that is certainly what they looked like and leak tested in mine as I replaced with generic yellow film caps I matched to within 1% of each other. Oh and yes, surprise surprise I have both models and can easily refute a lot of nonsense here. The SX-117 is quite a bit inferior in many areas, especially selectivity, but certainly far better overall performance than most of the bottom dwelling stuff Hallicrafters were turning out in the 60's and on the way to oblivion with most of the other leaders of the past.

Carl, I again respectfully disagree with your above assertion.

The capacitors used in the SX-117 and even late SX-100's were called paper but were actually high quality General Instruments film capacitors that are as perfect today as when they were installed. 

All of the Hal radios including the SR-150, SR-400, SR-400A, SR-2000 and others called capacitors PAPER to qualify them as components that participate in circuits that require stable, predictable, and linear components.  Both the paper and film caps fit that description.  The ceramic Z5u does not --- as published in any research paper or formal design document.

Please observe the url    http://k9axn.com/_mgxroot/page_10880.html

You will find the unmolested SX-117 photos of the selectivity switch and parts list revealing.

Those capacitors that you described as leaky paper were probably as good as new when you replaced them.

They are precisely as I described; High quality General Instruments FILM capacitors.  Dissect one for yourself.  Test them for Q, DF, leakage, aging, hysteresis, change with applied voltage, inductance, self resonance, whatever you have instruments to test for.  They are 100% qualified to participate in that resonant filter circuit; THE Z5U are absolutely not.  Every vendors engineering team was informed of the limitations of the Class 3 ceramics when they were first marketed over 50 years ago. 

Have a great day!

Kindest regards Jim K9AXN
 


 
Logged
Pages: Prev 1 [2] 3 4 5 6 7 ... 9 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!