Dumble ODS 3rd gen build, PT/HT query
Hi all,
Hope everyone is well.
I am currently building the ODS 3rd gen. I the bom it specifies a fender twin PT (022756) Hammond make an exact replacement model no 290fex. My issue is the schematic and the layout call for a 3.15v tap from the transformer but, the required PT doesn't have it. Am I missing something here? Is there supposed to be a way to connect the heater wires even without the 3.15v tap?
Any help would be greatly appreciated.
Thanks
45 Views
The 3.15 volts is for each side of the tube heaters. The Hammond 290FEX doesn't have a center tap (the center tap would connect to ground, splitting your 6.5 volt heater supply into two 3.25 volt legs.) You can easily make what is called an artificial center tap. You would use two 1/2 watt, 100 ohm resistors to connect each heater tap to ground. Most commonly done where the heater wires connect to the pilot light, but since the Dumble schematic is using an LED, you would need to ensure that it was connected before (on the transformer side) the 2 watt, 330 ohm resistors that is dropping the voltage to the LED. There are a ton of different examples online. Just search for "tube amp artificial heater center tap".