Because there is more than one circuit it is easy for mistakes to be made. The number of times that I have seen stuffups with 6AQ5 & the common pins 1&7 ......... people will insist on using valve pins as tags of convenience, often rushing, without fully understanding the pin outs

The easiest way to measure "B" current in a back biased set is to measure the voltage across the back bias resistor. Then "Ohms law" applies.

Normal variance in voltage is +/- 20%. A 6AQ5 with no signal & 250VDC will draw (quoted) 49.5mA. The voltage across a cathode resistor (when fitted) will tell you what current that valve is drawing.

E.g. To get -12.5V (for a 250V "B") for the 6AQ5 the 175 Ohm Back bias resistor would pass around 71mA (0.9 watt). I normally measure the current primary side with a clamp meter, or AVO 7X, if I have to.

I have a special cable made up to do that without risking getting zapped. The workshop RCD does work, as a cow decided that a cable was tasty as soon as I turned my back. They just love chewing plastic? There is nothing land based here, that is more destructive than a bored inquisitive cow.

I'll get back to the chassis soon. Decided to get the cord sorted and create a temporary paper dial add-on with frequency gradations marked to make alignment easier. Leaving the chassis alone for a while should make it less familiar and make it more likely to pick up any wiring mistakes.

Tags of convenience have been used on the signal transformers and rectifier - will keep an eye out for others.

"Avoiding getting zapped". Will have to do something similar to making up a special cord. On this occasion set up the meter with alligator clip leads, and then plugged in to the 240v- no hands anywhere near the leads. When I do things like this any exposed 240v stuff in a plastic box on the floor.
Have reformed caps using HT from a radio chassis through a current limiting resistor- all in a plastic box, this time with the lid on in case of bangs. Can't be left unattended and need to keep an eye on temperatures.

I see no practical reasons for measuring current mains side. We are interested in the B current. It is much safer on the secondary side anyway.

If you can, add up all of the plate & screen currents. you may need to get that from the valve data sheets. That will give you an idea of what it should draw.

The back bias resistor will give you the current draw.

"I see no practical reasons for measuring current mains side."

Not a lot of use I agree, but it is specified and can be measured easily.

Now checking all of the wiring, connection by connection startting with 6AQ5.

The voltage across the back bias is of considerable use, and a damn side safer. Because all of the cathode current is going through it, the only time it can be right is when everything is right, & drawing its correct current.