[Amps] QEX Innovative Tube Linear?

[Will Matney]

See below;

*********** REPLY SEPARATOR  ***********

On 7/8/06 at 12:31 AM Tom W8JI wrote:

>Hi Will,
>
>I'm still not sure I understand fully. I'll try one last 
>time.
>
>Will replied:
>>>> Again, no tube manufacturer ever gave warranties for 
>>>> sweep tubes in amplifiers (except GE). Every OEM bought 
>>>> from CECO or Richardson at one time, and the only 
>>>> warranties were given by the amplifier manufacturers 
>>>> themselves. At that, most amp manufacturers gave no 
>>>> warranties on sweep tubes. The M-2057, and 8950 are an 
>>>> exception as long as they were ran under the maximum 
>>>> design limits (design-maximum values). Those limits are 
>>>> what I posted earlier. These two sweep type tubes were 
>>>> the only two that GE specified as RF amplifier output 
>>>> tubes. Those are the only two I used besides 
>>>> experimenting with the Svetlana EL509.
>> Watch what is quoted as some here have saved the posts. I 
>> said "I would have been fired" for designing something 
>> outside the limits of a specification, not anyone else. I 
>> can tell you also that an inside engineer can tell you 
>> anything, and if you don't have it in writing, the 
>> manufacturer can surely back out on a warranty if they 
>> want to. The comparisons about someone losing a license 
>> concerned only myself (being fired) or an example about an 
>> engineer causing bodily harm or death of an end user 
>> because of faulty equipment. If a law suit begins, and 
>> something is designed past its stated maximums, the 
>> engineer can be held liable for it. Any engineer can tell 
>> you this. If they are the engineer in charge, they are 
>> responsible liability wise. The only out is to have a 
>> letter from the parts manufacturer giving a go-ahead for 
>> one particular use.
>> 900 Vdc is the design-maximum by GE, I'm not quoting RCA. 
>> Read the GE sheets and you'll see the difference. Most 
>> sweep tube curves don't show the design-maximum anode 
>> voltage. They stop about 1/2 way or a little below.>>>
>
>As I understand your answer, because the sweep tubes have no 
>warranty it doesn't really matter how you run them even for 
>long periods of time. If a tube has a warranty, momentarily 
>operating outside data sheet maximum CCS  operating specs 
>during tuning and adjustments is very bad engineering. On 
>the other hand, if the tube has no warranty it is acceptable 
>engineering to operate outside specs.


NO, sweep tubes had a warranty for TV service, not for RF amplifier service. The only two sweep type tubes that were warrantied for RF amplifiers by GE were the 8950, and the M-2057. Then the warranty was only good if you kept their operating conditions under the design-maximum value. No where did I say you can run any GE sweep tube above this value. Other manufacturers may be different like RCA, etc.. If your buying from them, then don't exceed their design-maximum value, or what service they are put into unless you plan on warranting them yourself. It doesn't matter how you run them, just don't expect to have a warranty from the tube manufacturer if you go over their maximum ratings.

>
>This is despite the fact that thoriated tungsten directly 
>heated tubes like 3-500Z's are not life-sensitive to 
>excessive anode voltage or emission current.
>As I also understand, in the case of sweep tubes, which have 
>metal oxide cathodes, there is no splatter or short term 
>problems when you operate outside published curves. 

Who said this? They splatter just like any other tube if not operated correctly. Plus in a sweep tube, it is much easier to destroy its life by operating them outside the published specs (higher than recommended anode voltage and cathode currents). Any indirectly heated cathode can be killed this way, sweep tubes being the easiest.

With a 
>3-500Z, it just won't work to do the very same thing.
>
>This is despite the fact metal oxide indirectly heated 
>cathode tubes are damaged by excessive anode voltage and 
>excessive emission even for short periods of time.

Correct, so why are you saying above it's ok to run them outside the specs or published curves? What I posted was the design-maximums for GE, not another brand except one Amperex, and one Phillips. At one time, when GE was in production on sweep tubes, you could get the curves up to the design maximums. They took up a whole 8-1/2 x 11 sheet. They used to send out a stack of info to the OEM who was using the tube. If buying large quantities, you could get inspection test results on every 250 tubes as they came off the line. Whats shown in most small tube books is only the tip of the iceberg on what's available engineering wise from GE. The GE application sheets had more info than the small handbooks by RCA, etc on receiving type tubes. If you can find them, GE published all these application sheets in several large 3 ring binders similar to the way Eimac did. There was typically 5 to 7 pages per tube.


>
>Is my understanding correct?

Nope.

One can run any tube anyway one wants, just don't expect to get a free replacement from the tube manufacturer when it goes poof if it's ran outside the specs....

>
>By the way, you might want to think about this. As Rich 
>says, for a given output power reducing HV generally does 
>not make an amplifier cleaner. The exception to this is when 
>reducing HV increases negative feedback. Since the output of 
>a GG amp is in series with the input, negative feedback (and 
>gain) is an almost direct function of anode load impedance. 
>There are two ways to increase negative feedback. One is to 
>reduce anode voltage, and optimize energy transfer to the 
>load at reduced voltage. The second way is to overtune the 
>amplifier and then reduce drive.
>
>If we don't reduce HV and overload to the same load 
>impedance, the amplifier is generally cleaner.
>
>This is important to know if we want to tune amplifiers for 
>the cleanest signal.
>
>1.) Reducing anode impedance increases negative feedback in 
>a GG amplifier
>2.) Running the highest possible voltage for a given output 
>generally increases both efficiency and IM performance, all 
>other things equal.
>
>It isn't correct to assume less HV results in improved IM 
>performance.
>
>73 Tom 
>
>
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73,

Will