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Bernie Schroder has found that the HV transformer degeneration can be slowed considerably by keeping the HV module cool and dry. | Bernie Schroder has found that the HV transformer degeneration can be slowed considerably by keeping the HV module cool and dry. | ||
The mod he was taught by Jim Willams involves replacing the tube rectifiers with NTE517 diodes. | The mod he was taught by [[Jim Willams]] involves replacing the tube rectifiers with NTE517 diodes. | ||
However, | However, this this reduces the load on the regulator circuit by about 1 Watt due to the lack of tube heater filaments. | ||
This forces the regulator past its design limit and can result in lack of regulation until the transformer heats up and more power is required due to losses. | This forces the regulator past its design limit and can result in lack of regulation, until the transformer heats up and more power is required due to losses. | ||
After changing to semiconductor diodes, it will be seen that grid pin 7 of V814 will be about 0 volts (fully on, with no swing to regulate) | After changing to semiconductor diodes, it will be seen that grid pin 7 of V814 will be about 0 volts (fully on, with no swing to regulate) | ||
in an attempt to force its anode (pin 6) to about +55 V, which is the screen input of the 6AU5 (pin 8). | in an attempt to force its anode (pin 6) to about +55 V, which is the screen input of the 6AU5 (pin 8). | ||
One way to remedy this is to replace the anode resistor coming off pin 6 of V814 (R803) from 56 kΩ to 82 kΩ. | One way to remedy this is to replace the anode resistor coming off pin 6 of V814 (R803) from 56 kΩ to 82 kΩ. | ||
Doing so changes the grid voltage on pin 7 of V814 to a comfortable | Doing so changes the grid voltage on pin 7 of V814 to a comfortable −0.8 V at switch-on. | ||
Again, this becomes more negative as the losses inside the transformer increase, but not by much if the transformer is healthy. | Again, this becomes more negative as the losses inside the transformer increase, but not by much if the transformer is healthy. | ||