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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Well, that's the nice thing about tubes, they give you advance warning of the magic smoke getting loose.
From earlier posts I got the idea that the operating point was 80ma and 5000v, a plate dissipation of 400w. But a real good design wouldn't be complete until you had proved that the 500w limit wouldn't be exceeded for any current setting, tube drop and line voltage. Well, not exceeded by too much for too long, at least.
X-ray, how did that work out? I've got a 4-400 here and would like to build an amp with it some day. Did you just connect both grids to ground?
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
Steve McConner wrote ...
X-ray, how did that work out? I've got a 4-400 here and would like to build an amp with it some day. Did you just connect both grids to ground?
No, you can't tie both grids together. The suppressor grid needs to be tied to B+ or to the plate. The control grid is grounded, and the input power from the exciter transmitter drives the cathode. In grounded-grid configuration, the input power adds to the output power, so it's not wasted energy. It's been many years (mid-1970's) since I built that 4-400 linear amp, so I don't recall many details, but you can find many examples in ham radio websites and forums.
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
Xray wrote ...
Steve McConner wrote ...
X-ray, how did that work out? I've got a 4-400 here and would like to build an amp with it some day. Did you just connect both grids to ground?
No, you can't tie both grids together. The suppressor grid needs to be tied to B+ or to the plate. The control grid is grounded, and the input power from the exciter transmitter drives the cathode. In grounded-grid configuration, the input power adds to the output power, so it's not wasted energy. It's been many years (mid-1970's) since I built that 4-400 linear amp, so I don't recall many details, but you can find many examples in ham radio websites and forums.
EDIT: Change "suppressor grid" to "screen grid". Sorry!
Registered Member #3447
Joined: Fri Nov 26 2010, 11:10PM
Location: North Jersey
Posts: 97
If you check under Current Regulator, you will notice that the current regulation control and instrumentation is limited to 80mA. Expected operating points are between 2-40mA. You will also notice in the current control circuitry that when the plate dissipation is above 500W, a warning LED lights on the instrumentation panel.
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Zero Bias Mode Triode Gain Equation
