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" <robert.chor...@berliner.com> To: <topband@contesting.com> 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
