[Techman]

So is the valve with the dimmer heater the same valve that is passing the lower current?

I think we’re getting to the bottom of this. It’s sounding like a corrode/oxidised connection issue. Measuring the heater current for each valve would be a good idea, but cutting into the circuitry around those old valve bases needs to be avoided. Measuring the current with extended crock clip leads with the valves removed would be the way to go, but I don’t think we’ll worry about that just yet. What you should do is remove the valves, noting which is which and with your meter set on the lowest ohms range (200 ohms?) carefully and accurately measure the resistance of the heaters of each valve at the valve pins. Note and report these readings, also note the reading on your meter with the test leads shorted together and report this reading, as we’ll need to subtract this reading from the two readings of the heaters. At this sort of low resistance, the resistance of the meter and its leads etc. are important and depending on the meter could be around 0.3 to 0.4 ohms. I’m suspecting that the ‘dimmer’ valve will show a higher resistance. If it does, then we’ll go from there. If it doesn’t, then we need to look at the valve bases, as it was a little bit inconclusive as to whether the fault was properly following the valves when they were swapped over.

Anyway, there’s no need to worry too much just yet as I personally have been here before with these valve types and this sort of problem.