06-10-2005, 07:38 PM
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Join Date: Apr 2005
| | Ameritron 811A
The bias is established by the diodes D19 thru D24 in the B-minus lead (center-tap of the filament transformer). Check the diodes; they should all be the same.
Looking at the schematic, point W6 (B-minus) is connected to W5 when the relay RLY-1B closes. B-minus continues up thru S-4 (this switch could be flakey), thru the current meter, M1. R-10 is a 330 ohm resistor in series with the negative side of the meter (make sure itís good) and, finally you have a 0.6 ohm resistor R-9 between B-minus and chassis ground.
not sure how the conversion to 572Bís were done; are there any resistors on the tube sockets themselves (maybe 47 ohms at 2 watts?), if so check value of all and make sure that they all are connected.
I cannot believe that the amplifier is eating tube with 1800 volts and no color showing; something is stopping you from drawing current. Replace the DC Blocking capacitor, C-13.