Topband: 8877 Tube

Discussion:

Topband: 8877 Tube

Chortek, Robert L

2012-11-14 23:56:42 UTC

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

Paul Christensen

2012-11-15 00:23:04 UTC

Permalink

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

Post by Chortek, Robert L
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

HAROLD SMITH JR

2012-11-15 01:10:52 UTC

Permalink

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

Post by Chortek, Robert L
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

_______________________________________________
Topband reflector - topband at contesting.com

2012-11-15 02:59:29 UTC

Permalink

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

Post by Chortek, Robert L
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

_______________________________________________
Topband reflector - topband at contesting.com
_______________________________________________
Topband reflector - topband at contesting.com

-----
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2012-11-15 02:56:11 UTC

Permalink

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" <w9ac at arrl.net>
To: <topband at contesting.com>
Sent: Wednesday, November 14, 2012 7:23 PM
Subject: Re: Topband: 8877 Tube

Post by Paul Christensen
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

Post by Chortek, Robert L
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

_______________________________________________
Topband reflector - topband at 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

John Harden

2012-11-15 11:17:35 UTC

Permalink

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

Post by ZR
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" <w9ac at arrl.net>
To: <topband at contesting.com>
Sent: Wednesday, November 14, 2012 7:23 PM
Subject: Re: Topband: 8877 Tube

Post by Paul Christensen
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

Post by Chortek, Robert L
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

_______________________________________________
Topband reflector - topband at contesting.com

Tom W8JI

2012-11-15 01:15:36 UTC

Permalink

Post by Chortek, Robert L
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

2012-11-15 02:49:32 UTC

Permalink

Is that at full power out or in standby?

Carl
KM1H

----- 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