Topband: 8877 Tube

[ZR]

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" <w0rihps at sbcglobal.net>
To: "Paul Christensen" <w9ac at arrl.net>; <topband at contesting.com>
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"
<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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