Topband: 8877 Tube

[HAROLD SMITH JR]

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.Chortek at berliner.com>
To: <topband at 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 at contesting.com 

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