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Author Topic: 3CPX800A  (Read 8111 times)
WG2Y
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Posts: 28




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« on: January 04, 2012, 01:23:39 PM »

I have an Ameritron AL800h that has a tube with intermittent flash over. I verified this with a hi pot tester. It was suggested to me to put a glitch resistor in series on the HV line to absorb the current spikes. I am not confident that this will be a long term solution. A new tube will be pricey. I have been told about medical pulls. Does anyone know where I could get one(none on Ebay).
Also is there any pro/con info on the Pro Tek brand as they are cheaper than Eimacs
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K4RVN
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Posts: 261




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« Reply #1 on: January 04, 2012, 02:11:13 PM »

From time to time Max Gain systems has some pulls from equipment. You might inquire with them on the chance they may have one.

http://www.mgs4u.com/RF-Microwave/transmittingtubes.htm

Frank
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K6AER
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Posts: 5745




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« Reply #2 on: January 04, 2012, 07:11:05 PM »

Medical pulls disappeared about 7-9 years ago with the medical equipment going solid state. If the tube flashes over it is due to oxygen or some metal spikes might be on the inside.

Either the tube will flash less with each discharge or it will get worse very quickly. Depends what is going on inside.

3CX800's are getting very rare if you want one cheap. New tubes are going for about $800-900.

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K2DC
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« Reply #3 on: January 05, 2012, 12:35:38 AM »

D & C Electronics also takes in good used tubes from time to time, but they are typically listed on eBay.  I got my latest spare 3CPX800 from them on eBay.  You might email them and asked to be notified if any come in.  A also bought a pair of spares once from K9AU, who has tubes listed on QTH.com occcasionally.

73,

Don, K2DC
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VK4TUX
Member

Posts: 37




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« Reply #4 on: January 05, 2012, 05:02:16 AM »

I have an Ameritron AL800h that has a tube with intermittent flash over. I verified this with a hi pot tester. It was suggested to me to put a glitch resistor in series on the HV line to absorb the current spikes. I am not confident that this will be a long term solution. A new tube will be pricey. I have been told about medical pulls. Does anyone know where I could get one(none on Ebay).
Also is there any pro/con info on the Pro Tek brand as they are cheaper than Eimacs

try;
http://www.wa8wzg.net/forsale.htm

http://www.ebay.com/itm/Eimac-3CX800A7-Vacuum-Tube-Ham-Radio-High-Power-Triode-RF-Power-Amplifier-/260928554305?pt=Vintage_Electronics_R2&hash=item3cc08dc541

http://www.ebay.com/itm/Pair-Eimac-3CX800A7-Ham-Radio-Tube-Badger-Estate-/290654077788?pt=LH_DefaultDomain_0&hash=item43ac55435c

Adrian ... vk4tux

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VK4DD
Member

Posts: 79




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« Reply #5 on: January 05, 2012, 10:27:24 PM »

I have an Ameritron AL800h that has a tube with intermittent flash over. I verified this with a hi pot tester. It was suggested to me to put a glitch resistor in series on the HV line to absorb the current spikes. I am not confident that this will be a long term solution. A new tube will be pricey. I have been told about medical pulls. Does anyone know where I could get one(none on Ebay).
Also is there any pro/con info on the Pro Tek brand as they are cheaper than Eimacs

try;
http://www.wa8wzg.net/forsale.htm

http://www.ebay.com/itm/Eimac-3CX800A7-Vacuum-Tube-Ham-Radio-High-Power-Triode-RF-Power-Amplifier-/260928554305?pt=Vintage_Electronics_R2&hash=item3cc08dc541

http://www.ebay.com/itm/Pair-Eimac-3CX800A7-Ham-Radio-Tube-Badger-Estate-/290654077788?pt=LH_DefaultDomain_0&hash=item43ac55435c

Adrian ... vk4tux



Its quite a common mistake to put normal 3cx800 in an amplifier which needs 3cpx800. The result is a big bang an blown up grid/ short to gnd. Cry

The 3cpx800 is the pulse version and can run on higher voltage. The normal version might be more linear?? Any way so don't buy these and look further for your 3CPX800. There used to be an EME guy which used these 3cpx800 also in 2m and 70cm amplifier. Lunar amplifiers yes thats him. He usally has original Eimac 3cpx800 but they won't come cheap.

73 Ron
VK4DD
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K2DC
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« Reply #6 on: January 05, 2012, 11:07:34 PM »

Don't worry at all about replacing the 3CPX800's with a pair of 3CX800's in an AL-800H.  Whil it is true that the 3CPX800 is pulse rated and designed to withstand higher plate voltages, your amp does not use those higher plate voltages and was not designed to require 3CPX800's exclusively.  Either will work just fine in pairs, although I don't know if it's wise to mix them.

BTW the second eBay listing in a previous post for a pair of 3CX800's from the Badger Estate is from D & C Electronics, and those tubes will be fully tested when they ship.

73,

Don, K2DC
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VK4TUX
Member

Posts: 37




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« Reply #7 on: January 05, 2012, 11:29:05 PM »

Don't worry at all about replacing the 3CPX800's with a pair of 3CX800's in an AL-800H.  Whil it is true that the 3CPX800 is pulse rated and designed to withstand higher plate voltages, your amp does not use those higher plate voltages and was not designed to require 3CPX800's exclusively.  Either will work just fine in pairs, although I don't know if it's wise to mix them.

BTW the second eBay listing in a previous post for a pair of 3CX800's from the Badger Estate is from D & C Electronics, and those tubes will be fully tested when they ship.

73,

Don, K2DC


Thankyou Don, Ron have a look here;

http://www.ameritron.com/Product.php?productid=AL-800H


"Output Power: 1500+ Watts PEP, dual 3CX800A7

All band operation: 160-15 meters including WARC bands. User modifiable for 12 and 10 meters.

Genuine Eimac tubes: Contains two Eimac 3CX800A7s
Tuned input circuit: Adjustable slug tuned input circuit."
 
Pays to do your homework sometimes, recommended are more correct than existing.

Adrian ... vk4tux
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VK4DD
Member

Posts: 79




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« Reply #8 on: January 06, 2012, 04:19:07 AM »

Yes that is correct Adrian. The CPX comment should be seen in general.
I posted this because the title said 3CPX800A.

TNX for the clarification.

Ron.
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QRPNEW
Member

Posts: 52




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« Reply #9 on: January 06, 2012, 04:50:35 AM »

I converted my Ten Tec Titan 425 to a pair of 3CPX800s. I changed the plate transformer. Its a real flame thrower, it puts out 3000 watts pep now and does not even break a sweat. It probably could go higher however I ran out of drive   and it popped the circuit breakers at 100 watts of drive.

 I got the  tubes at a hamfest for 100 dollars a pair as MRI pulls. They were dented for that price. I bought two pairs and they are both good. One 3cx800 had gone soft and I did not want to buy a new pair, I could have bought a new AMP!  I think this amp will last me into the grave now when run at 1kw.

I can highly recommend anyone  who is considering this conversion to do it. Eimac no longer recommends the stock 3cx800 for news designs. Soon these tubes will be the price of 8875's and impossible to find. I am even considering rebuilding a old Dentron MLA2500 to accommodate these 3cpx tubes when I am bored.

The 3CPX tubes are very  linear. I took it over to a friend who had a Yaesu MK5  and a Tek spectrum analyzer. We  think the tubes were even cleaner than the MK5 in A class. When you listen to the signal on a receiver it sounds like the radio has a brick wall filter the signal is so clean. All you hear is the phase noise from Yaesu, no splatter. Its incredible how clean these Eimac tubes are. My friends GS35 homebrew HF amp box sounds like a crud generator with the same test. Chalk and Cheese, you pay for what you gets.

Don't worry at all about replacing the 3CPX800's with a pair of 3CX800's in an AL-800H.  Whil it is true that the 3CPX800 is pulse rated and designed to withstand higher plate voltages, your amp does not use those higher plate voltages and was not designed to require 3CPX800's exclusively.  Either will work just fine in pairs, although I don't know if it's wise to mix them.

BTW the second eBay listing in a previous post for a pair of 3CX800's from the Badger Estate is from D & C Electronics, and those tubes will be fully tested when they ship.

73,

Don, K2DC


Thankyou Don, Ron have a look here;

http://www.ameritron.com/Product.php?productid=AL-800H


"Output Power: 1500+ Watts PEP, dual 3CX800A7

All band operation: 160-15 meters including WARC bands. User modifiable for 12 and 10 meters.

Genuine Eimac tubes: Contains two Eimac 3CX800A7s
Tuned input circuit: Adjustable slug tuned input circuit."
 
Pays to do your homework sometimes, recommended are more correct than existing.

Adrian ... vk4tux
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