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Re: [Amps] Dual 8877 HF amplifier RF design

To: <>, <>
Subject: Re: [Amps] Dual 8877 HF amplifier RF design
From: "Carl" <>
Date: Tue, 17 Dec 2013 18:14:21 -0500
List-post: <">>
I wouldnt say the 3CPX1500A7 is any tougher than the 8877 as it still has to run within its dissipation parameters. In true pulse service it can do that even with the higher B+

As far as a pair the Alpha 77SX did it as well as the many 2 hole AL-1500's that are out there; just remove the block off plate on the tube deck and do the work. If the homebrew layout is sloppy then tap the 10M coil with the Tune cap to step up the C requirement to resonate.

The output C isnt much higher than a grid driven 4-1000A and Ive put a pair of those on 160-10 several times during my building days.


----- Original Message ----- From: "Jim W7RY" <>
To: <>
Sent: Sunday, December 15, 2013 5:11 PM
Subject: Re: [Amps] Dual 8877 HF amplifier RF design


I've used both the WD7S triode board (in my current 8877 amplifier) and the G3SEK board in my 3CX800 amplifier. I would use the G3SEK board over the WD7S board but Ian's board doesn't have a filament timer or built or power transformer which I like on the WD7S board. This said, Ian's board is a bit smaller than the WD7S board. Both boards work very well and are both well designed. I don't use the hot switching detection on the WD7S board but I may add it in the future. In a mulit contesting station, RF can feed from one station to the other and prevent the amplifier from transmitting. (The Ten-Tec Titan was famous for this problem).

I also used the WD7S tuned input board on both of my amplifiers with some changes. Please see all of my pictures here for some ideas:

Getting 10 meters to work with 2 tubes is going to be tricky. You will probably have to use a L-C-L-C arrangement to be able to get the minimum plate tune C down to an achievable level.

Not sure why you need 2ea 8877 tubes but to each their own. In my opinion, the 8877/3CX1500 or its tougher brother, the 3CPX1500 is probably the BEST tube for an amateur linear amplifier.

Input and output antenna relay switching is also important. I have a writeup in the 2014 Radio Amateurs Handbook (chapter 24) about antenna relay sequencing thoughts.

Sounds like a great project! Keep us in the loop on your progress.
Jim W7RY

On 12/15/2013 4:19 AM, wrote:

I've been looking for designs, and examples for implementing, dual 2 x
8877s on HF.  I'm looking to build something that will cover 160m - 10m.

WD7S kindly sent through details of his auto-tune amplifier, and I'm
planning to use one of his tuner boards for the input of my amplifier.  I
don't want (or need) auto-tuning for the output though.  I'm going to use
a G3SEK board for control and metering.

If anyone has anything they could pass on, it would be very much
appreciated.  I've some experience of building valve amps, but only on
VHF, and only published designs. I'm not confident as a designer.



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