Maker Pro
Maker Pro

Mixed voltage sources



Jan 1, 1970
I am trying to understand the voltage sources on the schematic below.
It is a combination of voltage from Mains and the transformer secondaries.
I want to test the circuit in LTspice and pro to-board it.

I'm working on remaking a tube tester, but only for one tube
type. I tore apart a Working BK model 606 and matched the components to
the schematic.

I simulated and proto-boarded the tube heater circuit. (pins 4 & 5) I hooked a tube up to a 6.3 V transformer secondary lead.
I also tried a full wave bridge rectifier. It all worked, but that was veryelementary. I had planned on replacing the trans with two or three dedicated ones with single primaries and single secondaries. One for the heatersof the tube under test, one for the heaters of the 6BN8 in the test circuit, and one for plate/grid power.

Now I'm headed to the grid, cathode, and plate. I looked at the schematic more closely, and was completely mystified.
One secondary trans leads (6V) is paired with a primary lead for the heatercircuit (pins 4&5). This is for a 6BN8 tube that is part
of the testing circuit. Not the tube under test. The complimentary secondary lead is labeled 30V and goes to the grid test circuit. That's OK. The primary
half ends up at the 6BN8 plate. That's OK because the typical operating voltage for the Plate is 100V Max listed as 300V

My questions.
The schematic shows this mismatch coming from the transformer coils. Is this an autotransformer?
How do I set up an LTspice sim with the mismatched / multiple voltage sources for a circuit without a ground?
I'm also a bit nervous about pro to-boarding this circuit.