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Re: [Amps] Why 2 3CX800s instead of one 8877?

To: "Colin Lamb" <>, "Mike McCarthy,W1NR" <>, "Roger \(K8RI\)" <>, <>
Subject: Re: [Amps] Why 2 3CX800s instead of one 8877?
From: "Carl" <>
Date: Thu, 25 Apr 2019 17:40:50 -0400
List-post: <>
Since a pair of 3CX800's wont even come close to running hard in a 2 or 3 hole 76A series amp then a little careful surgery will do the trick. Remove enough of the anode cooler from both tubes so that they will fit with about 1/4" spacing.

Dont laugh, it is just a part of hams doing what works when needed.
I modified several 8874's decades ago to replace the 8873 in Heath SB-230 amps. At that time they were cheap as full power medical and other pulls. My own SB-230 modified for 6M and used for portable and roving has been fine since 1985.


----- Original Message ----- From: "Colin Lamb" <> To: "Mike McCarthy,W1NR" <>; "Roger (K8RI)" <>; <>
Sent: Tuesday, April 23, 2019 8:19 PM
Subject: Re: [Amps] Why 2 3CX800s instead of one 8877?

I am somewhat mystified by the messages. The Alpha 76A has 2 or 3 tubes 3CX400. But there is a difference. The 3 tube version you can plug one socket and then use 2 3CX800A7 tubes. They fit fine. I changed one and mounted the transformer inside the unit. It works fine.

There is a problem with the two tube version. If you change to tubes to 2 3CX800 tubes - the sockets are too close together so they do not fit. That would require more work because the holes and all the chimenys are too close together. I have a 2 hole amp and used the 3CX400 tubes. I run that amp at 1200 watts and it has run flawlessly for years.

I did a couple of other things to my amp. I installed a vertical array inside between two meters for grid response. Because these LEDs are much quicker that the meter it is much faster and that lets me monitor forward output with the meter. Then, I converted the output meter to read peak reading with a meter used for the Bird Wattmeter. I have about 6 amplifiers and with those two changes this amp is the one I use day after day.

73,  Colin  K7FM
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