MLA 2500 conversions

From NG9R

7/5/2007 9:12:54 AM (0 comments) Add Comment

I have seen several conversions using the Dentron MLA 2500 on the internet, but none are a simple as one I currently have on my desk.

The MLA 2500 originally used Eimac 8875 tubes that have become worth their weight in gold, if you can find them. I have seen many conversions to use other tubes, most requiring gutting the entire chassis and building a remote power supply, eliminating the usefulness of a compact desktop amp.

The one I currently have was done by another ham, W6TR, and is as simple as can be. The 8875 tubes were replaced with Eimac 8874's and a plenum was made from .010 fiberglass board epoxied together. The 8874 is a drop in replacement electrically and actually a bit smaller in diameter than the 8875. The plenum is simply a box that sits around both tubes with holes for the air to exhaust out the top and a hole in the back for a small blower to force air into the box. No power supply parts need be changed, the same sockets are used, the bias is the same and it runs as much if not more power than the original amp. The 8875 anode was rated for 350 watts and the 8874 is rated for 400 watts dissapation. The only real change is the blower added to the back of the chassis. I easily see 1000 watts out with 50 watts of drive and can run over 1200 watts out if I drive it harder. Check out my pictures for a couple of detail shots.

Has anyone else got a 2500 that they have converted to use different tubes?



NG9R