>According to a friend who had one, the early
>CENTURIANS kept full idle current,
>even in the stand-by mode!
>
The only way this could happen is if the bias potential during receive is
not what it is supposed to be.
>Apparently, they also had problems with the
>BIAS transistor which could explain excessive
>current conditions. Check the bias voltages
>and components.
>
Agreed, Tom. There must have been a large current surge through the
3-500Zs for the 15A-rated bias transistor to short. If the measured
potential between the filament CT and the chassis is zero V, I'm guessing
C-E shorted transistor.
- Possible Causes -
1. Anode to grid short caused by defective anode-cooler spotwelds (Eimac
only). -/- Visually inspect anode cooler alignment.
2. Air in envelope due to leaking glass/metal seal. -/- Test vacuum at
8kV on a high pot.
3. Intermittent VHF oscillation. -/- Measure the ohms of the VHF
suppressor resistor. Measure grid-filament breakdown potential. If the
breakdown V is less than 5 or 6 kV, a bent filament helix is indicated.
IMO, such oscillations can bend the filament helix. [See "Parasitics
Revisited" in the 9/94 *QST*]. Also inspect 10m contacts on bandswitch.
Damaged contacts indicate that such an oscillation may have occurred.
R. L. Measures, 805-386-3734, AG6K
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