Re: Topband: 8877 Tube
The Alpha 77-SX is a great amplifier with plenty of reserve. The plate voltage runs just under 4KV on the Hi-Power position. If you go to the larger transformers you are asking for trouble. The filter capacitor has to be changed to one with a 5 KV rating. When you do this you will push circuit components to their HV limit. There have been too many problems out there with those who have done this... 73, John, W4NU On 11/14/2012 9:56 PM, ZR wrote: The only problem with pushing an 8877 or the 3CPX to or over the 4KV limit is that it enhances the chance of instability. Carl KM1H - Original Message - From: "Paul Christensen" To: Sent: Wednesday, November 14, 2012 7:23 PM Subject: Re: Topband: 8877 Tube Bob, A non-issue. Many of us have been running 8877s with Ep of 4KV. For example, the typical no-load Ep of an Alpha 77Dx/Sx amp is right at the specified limit of 4KV. Some owners have been converting their 8877 amps over to the 3CPX1500A7 which has a much higher rated Ep since it was designed for pulsed service. Unless someone has access to a supply of pulse-rated tubes, I think it's waste of time unless the plate supply voltage is also increased. Paul, W9AC - Original Message - From: "Chortek, Robert L" To: Sent: Wednesday, November 14, 2012 6:56 PM Subject: Topband: 8877 Tube Wonder if someone can help with a technical question with the amp I use on 160 meters. The Spec Sheet for the 8877 tube lists the "Absolute Maximum Plate Voltage of 4000 Volts" for the tube, and also says in "typical operation" the plate voltage is between 2700 and 3500 volts. In my amp (Ameritron AL-1500), the plate voltage is 3750. My question is - should I be concerned (it's clearly below the maximum" but above the range that is considered "typical"? I just want to be sure I'm not adversely affecting the useful life of the tube. Any help would be appreciated. 73, Bob/AA6VB ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1427 / Virus Database: 2441/5395 - Release Date: 11/14/12 ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: 8877 Tube
The 5.5V is a ploy to get higher emission at the expense of operational life. It still has an 8877 filament. Eimac has been doing similar since WW2 with pulse versions of various tubes. Carl KM1H - Original Message - From: "HAROLD SMITH JR" To: "Paul Christensen" ; Sent: Wednesday, November 14, 2012 8:10 PM Subject: Re: Topband: 8877 Tube Bob and Paul, The 8877 has a 5 volt filament. The 3CPX1500A7 has a 5.5 volt filament. Many have been running the 8877 and 3CPX1500A7 with a Peter Dahl transformer at over 4kV and they work fine. Eimac says that the filament should be 5.0 volts +- 5% or 4.75 to 5.25 volts. This should be measured with a True RMS voltmeter. A friend had high line voltage and his actual filament voltage was 5.5 volts. He had lost several tubes with an open filament. After he lowered the voltage to 5.0 volts he has not lost a tube. He used a Varistor in the secondary to each tube. The 77SX has 2 filament windings. Price W0RI Bob, A non-issue. Many of us have been running 8877s with Ep of 4KV. For example, the typical no-load Ep of an Alpha 77Dx/Sx amp is right at the specified limit of 4KV. Some owners have been converting their 8877 amps over to the 3CPX1500A7 which has a much higher rated Ep since it was designed for pulsed service. Unless someone has access to a supply of pulse-rated tubes, I think it's waste of time unless the plate supply voltage is also increased. Paul, W9AC - Original Message - From: "Chortek, Robert L" To: Sent: Wednesday, November 14, 2012 6:56 PM Subject: Topband: 8877 Tube Wonder if someone can help with a technical question with the amp I use on 160 meters. The Spec Sheet for the 8877 tube lists the "Absolute Maximum Plate Voltage of 4000 Volts" for the tube, and also says in "typical operation" the plate voltage is between 2700 and 3500 volts. In my amp (Ameritron AL-1500), the plate voltage is 3750. My question is - should I be concerned (it's clearly below the maximum" but above the range that is considered "typical"? I just want to be sure I'm not adversely affecting the useful life of the tube. Any help would be appreciated. 73, Bob/AA6VB ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1427 / Virus Database: 2441/5395 - Release Date: 11/14/12 ___ Topband reflector - topband@contesting.com
Re: Topband: 8877 Tube
The only problem with pushing an 8877 or the 3CPX to or over the 4KV limit is that it enhances the chance of instability. Carl KM1H - Original Message - From: "Paul Christensen" To: Sent: Wednesday, November 14, 2012 7:23 PM Subject: Re: Topband: 8877 Tube Bob, A non-issue. Many of us have been running 8877s with Ep of 4KV. For example, the typical no-load Ep of an Alpha 77Dx/Sx amp is right at the specified limit of 4KV. Some owners have been converting their 8877 amps over to the 3CPX1500A7 which has a much higher rated Ep since it was designed for pulsed service. Unless someone has access to a supply of pulse-rated tubes, I think it's waste of time unless the plate supply voltage is also increased. Paul, W9AC - Original Message - From: "Chortek, Robert L" To: Sent: Wednesday, November 14, 2012 6:56 PM Subject: Topband: 8877 Tube Wonder if someone can help with a technical question with the amp I use on 160 meters. The Spec Sheet for the 8877 tube lists the "Absolute Maximum Plate Voltage of 4000 Volts" for the tube, and also says in "typical operation" the plate voltage is between 2700 and 3500 volts. In my amp (Ameritron AL-1500), the plate voltage is 3750. My question is - should I be concerned (it's clearly below the maximum" but above the range that is considered "typical"? I just want to be sure I'm not adversely affecting the useful life of the tube. Any help would be appreciated. 73, Bob/AA6VB ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1427 / Virus Database: 2441/5395 - Release Date: 11/14/12 ___ Topband reflector - topband@contesting.com
Re: Topband: 8877 Tube
Is that at full power out or in standby? Carl KM1H - Original Message - From: "Chortek, Robert L" To: Sent: Wednesday, November 14, 2012 6:56 PM Subject: Topband: 8877 Tube Wonder if someone can help with a technical question with the amp I use on 160 meters. The Spec Sheet for the 8877 tube lists the "Absolute Maximum Plate Voltage of 4000 Volts" for the tube, and also says in "typical operation" the plate voltage is between 2700 and 3500 volts. In my amp (Ameritron AL-1500), the plate voltage is 3750. My question is - should I be concerned (it's clearly below the maximum" but above the range that is considered "typical"? I just want to be sure I'm not adversely affecting the useful life of the tube. Any help would be appreciated. 73, Bob/AA6VB ___ Topband reflector - topband@contesting.com - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1427 / Virus Database: 2441/5395 - Release Date: 11/14/12 ___ Topband reflector - topband@contesting.com
Re: Topband: 8877 Tube
The Spec Sheet for the 8877 tube lists the "Absolute Maximum Plate Voltage of 4000 Volts" for the tube, and also says in "typical operation" the plate voltage is between 2700 and 3500 volts. In my amp (Ameritron AL-1500), the plate voltage is 3750. My question is - should I be concerned (it's clearly below the maximum" but above the range that is considered "typical"? I just want to be sure I'm not adversely affecting the useful life of the tube. If you are talking about Eimac, they generally obtained "typical operation" from a single test system under a variety of conditions. Typical operation is what Eimac found in a few test cases, and is not a limit or rigid specification. It might not even repeat out in the field. High voltage does not affect life at all in thoriated tungsten tubes (it cannot strip the cathode), and in oxide cathodes (like the 3CX1500A7) HV only affects tube life when HV gets so high it strips the protective electron cloud away from cathode. This causes cathode poisoning. (This of course assumes the tube does not arc, and a typical good 8877/3CX1500A7 will hold off 15 kV or more peak voltage so arcing is unlikely in a good tube. ) http://www.w8ji.com/vacuum_tubes_and_vaccum_tube_failures.htm 73 Tom ___ Topband reflector - topband@contesting.com
Re: Topband: 8877 Tube
Bob and Paul, The 8877 has a 5 volt filament. The 3CPX1500A7 has a 5.5 volt filament. Many have been running the 8877 and 3CPX1500A7 with a Peter Dahl transformer at over 4kV and they work fine. Eimac says that the filament should be 5.0 volts +- 5% or 4.75 to 5.25 volts. This should be measured with a True RMS voltmeter. A friend had high line voltage and his actual filament voltage was 5.5 volts. He had lost several tubes with an open filament. After he lowered the voltage to 5.0 volts he has not lost a tube. He used a Varistor in the secondary to each tube. The 77SX has 2 filament windings. Price W0RI Bob, A non-issue. Many of us have been running 8877s with Ep of 4KV. For example, the typical no-load Ep of an Alpha 77Dx/Sx amp is right at the specified limit of 4KV. Some owners have been converting their 8877 amps over to the 3CPX1500A7 which has a much higher rated Ep since it was designed for pulsed service. Unless someone has access to a supply of pulse-rated tubes, I think it's waste of time unless the plate supply voltage is also increased. Paul, W9AC - Original Message - From: "Chortek, Robert L" To: Sent: Wednesday, November 14, 2012 6:56 PM Subject: Topband: 8877 Tube > Wonder if someone can help with a technical question with the amp I use on > 160 >meters. > > The Spec Sheet for the 8877 tube lists the "Absolute Maximum Plate Voltage of >4000 Volts" for the tube, and also says in "typical operation" the plate >voltage >is between 2700 and 3500 volts. In my amp (Ameritron AL-1500), the plate >voltage >is 3750. My question is - should I be concerned (it's clearly below the >maximum" but above the range that is considered "typical"? I just want to be >sure I'm not adversely affecting the useful life of the tube. > > Any help would be appreciated. > > 73, > > Bob/AA6VB > > ___ > Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: 8877 Tube
Bob, A non-issue. Many of us have been running 8877s with Ep of 4KV. For example, the typical no-load Ep of an Alpha 77Dx/Sx amp is right at the specified limit of 4KV. Some owners have been converting their 8877 amps over to the 3CPX1500A7 which has a much higher rated Ep since it was designed for pulsed service. Unless someone has access to a supply of pulse-rated tubes, I think it's waste of time unless the plate supply voltage is also increased. Paul, W9AC - Original Message - From: "Chortek, Robert L" To: Sent: Wednesday, November 14, 2012 6:56 PM Subject: Topband: 8877 Tube Wonder if someone can help with a technical question with the amp I use on 160 meters. The Spec Sheet for the 8877 tube lists the "Absolute Maximum Plate Voltage of 4000 Volts" for the tube, and also says in "typical operation" the plate voltage is between 2700 and 3500 volts. In my amp (Ameritron AL-1500), the plate voltage is 3750. My question is - should I be concerned (it's clearly below the maximum" but above the range that is considered "typical"? I just want to be sure I'm not adversely affecting the useful life of the tube. Any help would be appreciated. 73, Bob/AA6VB ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Topband: 8877 Tube
Wonder if someone can help with a technical question with the amp I use on 160 meters. The Spec Sheet for the 8877 tube lists the "Absolute Maximum Plate Voltage of 4000 Volts" for the tube, and also says in "typical operation" the plate voltage is between 2700 and 3500 volts. In my amp (Ameritron AL-1500), the plate voltage is 3750. My question is - should I be concerned (it's clearly below the maximum" but above the range that is considered "typical"? I just want to be sure I'm not adversely affecting the useful life of the tube. Any help would be appreciated. 73, Bob/AA6VB ___ Topband reflector - topband@contesting.com
