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How to power up again a stored SSPA?

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Feb 3rd, 2011 at 4:41am  
Sir we have our spare AWMT SSPA C100-CSE and stored it for atleast 3 months without any power applied. Somebody told us that it is better to apply power on the unit even we are not using it. Is there a proper way on how to power it up again like we have to apply input signal and try transmitting it or we can just power it up then keep it on standby?

Thanks.
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Reply #1 - Feb 3rd, 2011 at 7:07am  
Hello,

I'm not sure why is it recommended to apply power on the unit if it is not used. I never heard such a recomendation and I can not understand the logic behind it. Did you provided with an explanation as well?

Anyway, if you do power the SSPA, make sure you terminate it in a safe manner, meaning connecting it to a dummy load. The transmission, especially at high-power SSPA and BUC could be harmful and even cause blindness!
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« Last Edit: Feb 3rd, 2011 at 11:50am by Admin1 »  
 
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Reply #2 - Feb 4th, 2011 at 1:22am  
My friend told me that they store their SSPA for a long time and when they use it again its not working anymore, considering that they store it on a proper way. (cleaning it, disconnecting cables, storing on a cool dry place etc.).

Another thing sir, the unit has a power consumption of 2000 W, do this mean when I power this thing up it will consume 2000 W on our UPS even it was just on standby?
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Reply #3 - Apr 26th, 2011 at 1:34am  
If its what I think you and your friend are talking about, its called degassing.  Basically when you store an HPA or SSPA for a long period of time you have to degas it to burn all the unwanted stray air that may have built up in the tube during storage to prevent damage to the tube upon putting it into operation.  we usually do this by putting the hpa on a dummy load, turning on rf, and setting the u/c power to -30dbm for an hour and then increase it by 3dbm every 30 minutes after.


And be sure to check this site out. 

http://photos.imageevent.com/qdf_files/technicalgoodies/training/DeGassing%20of%...

"Avoiding Gassy Tubes : This is the easy part. All a customer has to do to avoid a gassy TWT tube is to
operate the amplifier, in High Voltage On, for a period of 24 hours every three months. At the end of this
operational cycle, verify that the quiescent Helix Current has returned to a very low value (typically
13mA)
and deactivate the amplifier. If this is done at a minimum of every three months, the customer
should not have any problems with Gassy TWT tubes."
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Reply #4 - Apr 26th, 2011 at 7:20am  
Thank you for the useful information Smiley

But I believe degassing is required for TWTA only and not for SSPA, as SSPA amplifies in a different manner, without a tube, isnt it?

Regards,
Nimrod
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Reply #5 - Apr 26th, 2011 at 8:04am  
Thank you sir for the information, it still useful for me since we are also maintaining TWT HPA.

thanks..
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Reply #6 - Apr 26th, 2011 at 11:23am  
Now that you mention it oasis, after posting this last night I started thinking about the sspa haha, and that is my question now, in what manner does it amplify? 

After looking through my manuals for the twt system and the sspa system, I realized that its the twt system that has the tube, i work with both systems so i had a brain fart.

And for the degassing procedure its actually starting at -30dbm with the upconverter muted and only high power switched on for an hour, then making tx power +30dbm for an hour and go down in increments of 3dbm every 30 minutes after that until around 15dbm, you should be good then. 

Sorry for the confusion!Wink
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Eric Johnston
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Reply #7 - Apr 26th, 2011 at 2:29pm  
Keep a record of the helix current in a log book.  The pdf document above actually says 1-3 mA, not 13 mA.

Some TWTA have typical helix current of 0.5mA and helix current trip alarm at 4 mA.

Some very high power TWTA have maximum helix current of 15 mA.

Regarding cathode current, this is normally maintained at a steady value over tube lifetime by gradually altering the first anode voltage as the cathode gradually degrades.  Once the cathode gets really bad the cathode current starts to drop. Worth recording these values also in a log book.

I note the procedure described for de-gassing using short (1 day) ON periods every few months.

My opinion is that it is not a good idea to turn off tubes that have been on for a long time, 6 months or more. The surface of the cathode becomes ultra clean and dirt is concentrated down the collector end of the tube.  When switched off the dirt comes back up the tube and poisons the cathode.

Regarding SSPAs, the secret to long life is keeping them cool and not overdriving them. High temperatures and slight over-voltage spikes cause gradual deterioration of semi-conductors.

Best regards, Eric.
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Reply #8 - Apr 27th, 2011 at 1:35am  
Thank you for the info sir, but sir eric what do you suggest on our spare sspa is it much better to store it without power or we store it on standby and properly terminated?
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Eric Johnston
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Reply #9 - Apr 27th, 2011 at 9:58am  
The advice in the pdf document is based on the theory that the tube is gradually leaking and, when left switched off,  needs de-gassing for 1 day every few months. Ask the manufactuer of your tube if they agree.

Powering on and off causes thermal cycling and this action in itself will stress joints etc.

According to my idea, if a tube has been on for six months, then it is best left on all the time.

Best regards, Eric.
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« Last Edit: Apr 27th, 2011 at 2:12pm by Admin1 »  
 
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Reply #10 - Apr 28th, 2011 at 2:36am  
Yes what would the proper procedure for powering up an SSPA after a long duration of storage be Eric?

I have never heard of any type of procedure ken, our sspa has been very reliable and during our formal training on the system the subject never did arise on a procedure for replacing the sspa with the spare sspa.  I guess it may depend on which system you have, this one seems to be just a plug and play. 

Eric can you clerify?
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Reply #11 - Apr 28th, 2011 at 10:29am  
Yes sir jets our SSPA is working without any problem including a mirror back-up, the one that I want to know on how to store is our spare SSPA which we are not using for more than a year. I just want to prevent a scenario where we needed it and we can't use it because we improperly stored it.

thanks,

ken
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Eric Johnston
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Reply #12 - Apr 28th, 2011 at 11:23am  
If I power up any piece of electronic equipment that has been off for a very long time my main concern is the large value electolytic power supply capacitors in the power supply.  I've certainly had numerous returned-from-the-field 'boxes' go bang when first switched on with burned out parts in the power supply area.  Many power supplies have inrush current limitors and spike supressors but these components do fail or explode at times.

For old electronic equipment pwered up afer a long time some people suggest you should try to limit the inrush current by using a Variac transformer and reform the electrolytic capacitors slowly.  I suggest you ask your SSPA manafacturer.  The sequencing of the bias and power voltage supplies to high power microwave transistors is critical, so follow the manufacturers recommendations. It is very easy to destroy the power amplifier transistors by applying the wrong voltages or in wrong sequence.

Best regards, Eric.
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