Topband
[Top] [All Lists]

Re: Topband: 8877 Tube

To: topband@contesting.com
Subject: Re: Topband: 8877 Tube
From: John Harden <jhdmd@bellsouth.net>
Date: Thu, 15 Nov 2012 06:17:35 -0500
List-post: <topband@contesting.com">mailto:topband@contesting.com>
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

_______________________________________________
Topband reflector - topband@contesting.com

_______________________________________________
Topband reflector - topband@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


_______________________________________________
Topband reflector - topband@contesting.com


_______________________________________________
Topband reflector - topband@contesting.com

<Prev in Thread] Current Thread [Next in Thread>