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" <w9ac@arrl.net>
To: <topband@contesting.com>
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"
<Robert.Chortek@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
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