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Hi,I owned a Loftin White 2a3 SE DC amp for quiet some time. I wanted to mod it so it can accept both 2a3 and 45 tubes because I have a pair of 45.
Can anyone tell me if I can plug in the 45 without any mod? Or if mod is necessary, what do I need to do?
Many thanks
Follow Ups:
You will need to switch in more resistance in the cathode of the output tube. The 45 operates with less current (35mA vs 50 to 60mA for the 2A3), so you will need to increase the resistance to get the necessary voltage differential (bias voltage) between the driver output and the cathode of the 45 as well as voltage offset for the driver. It is not easy for a beginner to balance (but also not too hard to figure out if you know Ohms law and tube characteristic curve). If you need specific help, you will need to post more information about your circuit.
Thanks. I will try to find a circuit diagram of loftin white and post the link. The thing aboout my amp is that it had been modified by previous owner to direct couple. I was told that other than that, everything else was the same as the original loftin white.
The term "Loftin White" actually describes a broad class of amp designs, whose only common feature is that they are direct coupled. That's why nobody can say how to make the conversion without seeing the particular circuit first. The real original design is actually a fairly bad (noisy) amplifier, mostly because it dates from a time when capacitors larger than 4uF were nearly impossible to find. It seems to have used a type 24 tetrode and a type 50 power tube.
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