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3CPX800A7 testing questions
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05/03/2019 20:55
I have acquired an NMR linear amp made by AMP UK using two 3CPX800A7 tubes. It's bought "as seen and untested" Apart from the RF power meter smashed and a coupling centre insulator missing on one of the two 1000pF vac variables all LOOKS well. These tubes are hard to find and expensive so I want to test them first, as best I can. I have the usual meters and a decent Hi-Pot tester, what's the safest way to ensure their functionality before powering it up? I don't have the pin configuration for them, so if anyone has them, or a link to them I need that info first :) The amp is designed for 400kHz to 1MHz, so I am toying with using it on MF at some stage. My Eimac Power Grid Tubes book doesn't give the pin configuration and surprisingly Googling hasn't found them either. Thanks. If the tubes are good I have a bargain, if not I have a good source of some nice bits. -- Best Regards, Chris Wilson. mailto: chris@... |
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The bible for tubes is here.
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3CX800A7 is listed. 73, Alek. VK6APK On 6/03/2019 5:02 AM, Chris Wilson chris@... [ham_amplifiers] wrote:
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From sunny Binningup Family Businesses: SP Electrical. www.spelectrical.net.au The Velvet Fox. Smart Design Electrical. Perth Interiors. |
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Bob Naylor
Will wanna keep in contact with you for sure. I know all about finally meeting the love of my life, like you did. Too bad for all of us it took so long. That means we all have to make the most of the years we all have left. Take care and say hi to Deena, Bob From: "Chris Wilson chris@... [ham_amplifiers]" To: ham_amplifiers@... Sent: Tuesday, March 5, 2019 1:31 PM Subject: [ham_amplifiers] 3CPX800A7 testing questions
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05/03/2019 20:55 I have acquired an NMR linear amp made by AMP UK using two 3CPX800A7 tubes. It's bought "as seen and untested" Apart from the RF power meter smashed and a coupling centre insulator missing on one of the two 1000pF vac variables all LOOKS well. These tubes are hard to find and expensive so I want to test them first, as best I can. I have the usual meters and a decent Hi-Pot tester, what's the safest way to ensure their functionality before powering it up? I don't have the pin configuration for them, so if anyone has them, or a link to them I need that info first :) The amp is designed for 400kHz to 1MHz, so I am toying with using it on MF at some stage. My Eimac Power Grid Tubes book doesn't give the pin configuration and surprisingly Googling hasn't found them either. Thanks. If the tubes are good I have a bargain, if not I have a good source of some nice bits. -- Best Regards, Chris Wilson. mailto: chris@... |
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Bob Naylor
I don't know how that went here. Sorry guys. Bob ?WE6C From: "Bob Naylor wotbob01@... [ham_amplifiers]" To: "ham_amplifiers@..." Sent: Tuesday, March 5, 2019 3:01 PM Subject: Re: [ham_amplifiers] 3CPX800A7 testing questions
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Will wanna keep in contact with you for sure. I know all about finally meeting the love of my life, like you did. Too bad for all of us it took so long. That means we all have to make the most of the years we all have left. Take care and say hi to Deena, Bob From: "Chris Wilson chris@... [ham_amplifiers]" To: ham_amplifiers@... Sent: Tuesday, March 5, 2019 1:31 PM Subject: [ham_amplifiers] 3CPX800A7 testing questions
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05/03/2019 20:55 I have acquired an NMR linear amp made by AMP UK using two 3CPX800A7 tubes. It's bought "as seen and untested" Apart from the RF power meter smashed and a coupling centre insulator missing on one of the two 1000pF vac variables all LOOKS well. These tubes are hard to find and expensive so I want to test them first, as best I can. I have the usual meters and a decent Hi-Pot tester, what's the safest way to ensure their functionality before powering it up? I don't have the pin configuration for them, so if anyone has them, or a link to them I need that info first :) The amp is designed for 400kHz to 1MHz, so I am toying with using it on MF at some stage. My Eimac Power Grid Tubes book doesn't give the pin configuration and surprisingly Googling hasn't found them either. Thanks. If the tubes are good I have a bargain, if not I have a good source of some nice bits. -- Best Regards, Chris Wilson. mailto: chris@...
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¿ªÔÆÌåÓýThe 3CPX800A7 is essentially the same as the 3CX800A7.? The main difference is that the 3CPX800A7 is pulse rated and has a higher arc-over rating.? Consequently, it can handle higher plate voltage.? The pulse rated tube has an arc over rating of 7,000 volts so it can handle 3,500 volts on the plate whereas the standard tube has an arc-over rating of 5,000 volts and is limited to 2,500 Volts on the plate. ? Unless the tubes have a direct short cold static testing is not going to do you too much good.? The only surefire way to test a tube is in the circuit it is designed for or in a test fixture that is designed to supply the proper operating? voltages etc.? Quite often a tube that tests good for shorts and other defects while cold will fail under test when it has reached the normal operating temperature. ? Unfortunately, if the tubes have any serious defects you might run the risk of ¡°blowing¡± the amp up.? Also, if it has been sitting for an extended period of time it would be a good idea to bring the amp up very slowly on a Variac. ?The electrolytic caps used in many amps do not do well if they are not ¡°reformed¡± on a regular basis.? There is no guarantee that the caps will do well even if brought up slowly, but you have a much better chance of things not going up in smoke.? The Variac I use has voltage and current meters so that I can monitor what is going on.? If I see an unexpected sharp rise in current I can stop before something goes boom. ? 73, ? Steve ? From: ham_amplifiers@... [mailto:ham_amplifiers@...]
Sent: Tuesday, March 05, 2019 4:02 PM To: ham_amplifiers@... Subject: [ham_amplifiers] 3CPX800A7 testing questions ? ?
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Hello Alek,
Wow, that's a comprehensive list, thanks Alek, appreciated :) Best regards, Chris 2E0ILY mailto:chris@... APvbch> APvbch> APvbch> APvbch> APvbch> APvbch> The bible for tubes is here. APvbch> APvbch> APvbch> APvbch> 3CX800A7 is listed. APvbch> APvbch> 73, Alek. VK6APK APvbch> APvbch> On 6/03/2019 5:02 AM, Chris Wilson chris@... [ham_amplifiers] APvbch> wrote: >> >> 05/03/2019 20:55 >> >> I have acquired an NMR linear amp made by AMP UK using two 3CPX800A7 >> tubes. It's bought "as seen and untested" Apart from the RF power >> meter smashed and a coupling centre insulator missing on one of the >> two 1000pF vac variables all LOOKS well. These tubes are hard to find >> and expensive so I want to test them first, as best I can. I have the >> usual meters and a decent Hi-Pot tester, what's the safest way to >> ensure their functionality before powering it up? I don't have the pin >> configuration for them, so if anyone has them, or a link to them I >> need that info first :) The amp is designed for 400kHz to 1MHz, so I >> am toying with using it on MF at some stage. My Eimac Power Grid Tubes >> book doesn't give the pin configuration and surprisingly Googling >> hasn't found them either. Thanks. >> >> If the tubes are good I have a bargain, if not I have a good source of >> some nice bits. >> >> APvbch> APvbch> -- APvbch> From sunny Binningup APvbch> APvbch> Family Businesses: APvbch> SP Electrical. www.spelectrical.net.au APvbch> The Velvet Fox. APvbch> Smart Design Electrical. APvbch> APvbch> Perth Interiors. APvbch> APvbch> APvbch> APvbch> |
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Hello 'Selcor',
Wednesday, March 6, 2019 Thanks a lot for the comprehensive reply. The amp uses this transformer, maybe with a doubler or tripler, it's hard to see without some dismantling. What HT should I test with from the Hi-Pot? Best regards, Chris 2E0ILY mailto:chris@... Ssvnh> Ssvnh> Ssvnh> Ssvnh> Ssvnh> Ssvnh> The 3CPX800A7 is essentially the same as the 3CX800A7. The Ssvnh> main difference is that the 3CPX800A7 is pulse rated and has a Ssvnh> higher arc-over rating. Consequently, it can handle higher Ssvnh> plate voltage. The pulse rated tube has an arc over rating of Ssvnh> 7,000 volts so it can handle 3,500 volts on the plate whereas Ssvnh> the standard tube has an arc-over rating of 5,000 volts and is Ssvnh> limited to 2,500 Volts on the plate. Ssvnh> Ssvnh> Unless the tubes have a direct short cold static testing is Ssvnh> not going to do you too much good. The only surefire way to Ssvnh> test a tube is in the circuit it is designed for or in a test Ssvnh> fixture that is designed to supply the proper operating Ssvnh> voltages etc. Quite often a tube that tests good for shorts Ssvnh> and other defects while cold will fail under test when it has Ssvnh> reached the normal operating temperature. Ssvnh> Ssvnh> Unfortunately, if the tubes have any serious defects you might Ssvnh> run the risk of blowing the amp up. Also, if it has been Ssvnh> sitting for an extended period of time it would be a good idea Ssvnh> to bring the amp up very slowly on a Variac. The electrolytic Ssvnh> caps used in many amps do not do well if they are not Ssvnh> reformed on a regular basis. There is no guarantee that the Ssvnh> caps will do well even if brought up slowly, but you have a Ssvnh> much better chance of things not going up in smoke. The Variac Ssvnh> I use has voltage and current meters so that I can monitor what Ssvnh> is going on. If I see an unexpected sharp rise in current I Ssvnh> can stop before something goes boom. Ssvnh> Ssvnh> 73, Ssvnh> Ssvnh> Steve Ssvnh> Ssvnh> From: ham_amplifiers@... Ssvnh> [mailto:ham_amplifiers@...] Ssvnh> Sent: Tuesday, March 05, 2019 4:02 PM Ssvnh> To: ham_amplifiers@... Ssvnh> Subject: [ham_amplifiers] 3CPX800A7 testing questions Ssvnh> Ssvnh> Ssvnh> 05/03/2019 20:55 Ssvnh> I have acquired an NMR linear amp made by AMP UK using two 3CPX800A7 Ssvnh> tubes. It's bought "as seen and untested" Apart from the RF power Ssvnh> meter smashed and a coupling centre insulator missing on one of the Ssvnh> two 1000pF vac variables all LOOKS well. These tubes are hard to find Ssvnh> and expensive so I want to test them first, as best I can. I have the Ssvnh> usual meters and a decent Hi-Pot tester, what's the safest way to Ssvnh> ensure their functionality before powering it up? I don't have the pin Ssvnh> configuration for them, so if anyone has them, or a link to them I Ssvnh> need that info first :) The amp is designed for 400kHz to 1MHz, so I Ssvnh> am toying with using it on MF at some stage. My Eimac Power Grid Tubes Ssvnh> book doesn't give the pin configuration and surprisingly Googling Ssvnh> hasn't found them either. Thanks. Ssvnh> If the tubes are good I have a bargain, if not I have a good source of Ssvnh> some nice bits. |
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If the? tube is rated fo? 3.5 kv, it should hipot? ? a lot more than? ?double that.? ?When driven? ?to max out, the RF? voltage in the? PI? / PI-L? will back feed via the plate block cap...and superimpose itself onto the? tube's? B+? ? DC? voltage.? ?Typ the? total? voltage will be a? little bit less than? double the? key down? loaded? B+? value.?
Any good? 3-500Z? will hi pot test to? 12-16 kv.? ?A? 3CX-3000A7? will? easily? hi pot test to? 20 kv.? ? The? 3x10/15/20? all hi pot test easily to 30 kv.?? Once tube is warmed up? for? 20 mins......with NO B+ applied, then check for shorts? etc.? ?That's when u can get cathode to heater shorts or cathode to grid? shorts.? ?Buddy with the? YC-156? amp went through 12 tubes....? just to get 3? good ones.? ?The 9 bad ones all developed? ?shorts..... but only? after the? heater was on for? 5-10 mins.? If u dont? see any shorts? after? 20 mins... ( test one tube at a time).... then do the hi pot test on each individual tube... removed from? socket, on the bench.? ? Let us know what they hi pot to.? ?Typ hi pot test is run up to aprx 5-10 microamps. Jim? ?VE7RF |
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Hello jim.thom@...,
Thanks Jim, very helpful, work has sidetracked me for a while but I will post back as to what i find but I don't think my Hi-Pot tester goes over 8kV Best regards, Chris 2E0ILY mailto:chris@... jttnh> jttnh> jttnh> jttnh> jttnh> jttnh> If the tube is rated fo 3.5 kv, it should hipot a lot jttnh> more than double that. When driven to max out, the RF jttnh> voltage in the PI / PI-L will back feed via the plate block jttnh> cap...and superimpose itself onto the tube's B+ DC jttnh> voltage. Typ the total voltage will be a little bit less jttnh> than double the key down loaded B+ value. jttnh> Any good 3-500Z will hi pot test to 12-16 kv. A jttnh> 3CX-3000A7 will easily hi pot test to 20 kv. The jttnh> 3x10/15/20 all hi pot test easily to 30 kv. jttnh> Once tube is warmed up for 20 mins......with NO B+ applied, jttnh> then check for shorts etc. That's when u can get cathode to jttnh> heater shorts or cathode to grid shorts. Buddy with the jttnh> YC-156 amp went through 12 tubes.... just to get 3 good jttnh> ones. The 9 bad ones all developed shorts..... but only jttnh> after the heater was on for 5-10 mins. jttnh> If u dont see any shorts after 20 mins... ( test one tube jttnh> at a time).... then do the hi pot test on each individual jttnh> tube... removed from socket, on the bench. jttnh> Let us know what they hi pot to. Typ hi pot test is run up to aprx 5-10 microamps. jttnh> Jim VE7RF jttnh> |
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