Newmember here! Has anyone have knowledge / experience relating to a Maco / Brute Seventy-Five linear Amplifier? Note: Estimated manufacturing date: 1977.
Thank you for the information. Being a nostalgic type of guy, I recently acquired an original Brute Seventy-Five. As per the factory tag, the unit is set-up for 21 MHz. The M2057 tube has not been installed and it is wrapped / enclosed in a protective box. It appears that this unit was never used because the plastic protective wrap is still attached on the front panel. The plan is to convert the unit from 21 MHz to 27 MGz and see what happens.It was made in several different versions.
Most of them had a bad habit of breaking into oscillation, holding itself keyed up after you unkey the radio. Tends to burn up the tube.
It originally used a large tube called the "M2057". It was a custom version of the 8950 tube, wider with a higher heat rating. Both of these are now rare and expensive, 30-plus years after they quit making them.
It was built both as a grounded grid (cathode driven) amplifier, and also as a grounded-cathode grid-driven "modulator" design.
So yeah, it's not just one amplifier. It's a whole family of them.
The one single, simplest thing that settles this model down has to do with the coax that carries the tube's output power from the Load control on the front panel to the relay alongside the rear panel.
The factory did not connect the shield of the coax that makes this connection. Causes feedback issues. Simply grounding the shield braid of that coax at each end will stop a lot of bad behavior.
73
It only does it on one socket, either tube you plug in that socket starts to turn red.
The factory did not connect the shield of the coax that makes this connection. Causes feedback issues. Simply grounding the shield braid of that coax at each end will stop a lot of bad behavior.
If the .005 caps, that go to ground on the tube, are bad will that cause the tube to turn red?