Calculator
Example Data Table
| Setup | B+ V | Plate mA | Screen V | Screen mA | Rk Ω | Plate V | Plate W |
|---|---|---|---|---|---|---|---|
| Conservative build | 420 | 55 | 275 | 5 | 300 | 396.77 | 21.82 |
| Nominal build | 450 | 65 | 300 | 6 | 270 | 424.66 | 27.60 |
| High current check | 475 | 72 | 315 | 8 | 250 | 448.16 | 32.27 |
Formula Used
Cathode current: Ik = Ia + Ig2
Cathode voltage: Vk = Ik × Rk
Plate path drop: Vdrop plate = Ia × Rdc
Screen drop: Vdrop screen = Ig2 × Rg2
Plate-to-cathode voltage: Vak = B+ − Vdrop plate − Vk
Screen-to-cathode voltage: Vg2k = Vscreen − Vdrop screen − Vk
Grid-to-cathode voltage: Vg1k = Vgrid − Vk
Plate dissipation: Pplate = Vak × Ia
Screen dissipation: Pscreen = Vg2k × Ig2
Estimated output power: Pout = Vswing² ÷ (2 × Load) × Efficiency
How To Use This Calculator
Enter the supply voltage that feeds the plate circuit.
Add the expected plate current from the tube data sheet.
Enter the screen supply and screen current values.
Add the cathode resistor value for cathode biased stages.
Use zero grid voltage for grounded grid return designs.
Use a negative value for fixed bias designs.
Add output transformer primary impedance as the load.
Press Calculate and review voltage, power, and safety status.
Use CSV or PDF export for design notes.
Beam Tetrode Voltage Calculation Guide
Purpose Of The Calculator
A beam tetrode stage needs careful voltage planning. The plate, screen, grid, and cathode all interact. A change in one value can shift the whole operating point. This calculator helps you test those relationships before assembly. It supports cathode bias and fixed bias layouts. It also checks dissipation against chosen limits.
Why Voltage Checks Matter
Plate voltage is not always equal to supply voltage. Wiring resistance and transformer resistance create a small drop. Cathode bias also raises the cathode above ground. The actual tube voltage is measured from plate to cathode. Screen voltage must be checked the same way. A screen can overheat before the plate looks unsafe.
Bias And Current Planning
Bias sets the idle condition of the tube. With cathode bias, the cathode resistor creates bias voltage. With fixed bias, the grid is driven negative. The calculator combines both ideas in one result. Grid-to-cathode voltage shows the real bias value. This helps compare your design with tube curves.
Dissipation And Safety
Dissipation is voltage multiplied by current. It becomes heat inside the tube. A safe design leaves margin below the published rating. The safety margin field lets you choose that limit. For example, ninety percent keeps some room for variation. Tube age, wall voltage, and load changes can raise stress.
Load And Power Estimate
The reflected output load affects voltage swing. A larger load can increase voltage demand. A smaller load can increase current demand. This tool estimates output power from swing and efficiency. It is a planning estimate, not a full tube curve model. Final designs still need measurement under real conditions.
Construction Notes
Use these results while planning chassis layout and wiring. Keep high voltage nodes spaced safely. Rate resistors above their calculated wattage. Allow ventilation around power tubes and hot parts. Confirm transformer ratings before final construction. Record every result for later service work.
FAQs
What is plate-to-cathode voltage?
It is the effective plate voltage across the tube. It equals supply voltage minus plate path drop and cathode voltage.
Why is screen voltage calculated separately?
The screen grid uses its own supply path. Its dropping resistor and current can lower the real screen-to-cathode voltage.
Can I use this for cathode bias?
Yes. Enter the cathode resistor value. The calculator estimates cathode voltage from plate current plus screen current.
Can I use this for fixed bias?
Yes. Enter the fixed grid voltage as a negative value. Keep cathode resistance at zero if the cathode is grounded.
What does plate dissipation mean?
Plate dissipation is heat produced at idle. It equals plate-to-cathode voltage multiplied by plate current.
Why add a safety margin?
A margin helps cover tube variation, high wall voltage, measurement error, and heat buildup during long operation.
Is the output power exact?
No. It is an estimate based on load, voltage swing, and efficiency. Real output depends on curves, transformer loss, and distortion limits.
Should I verify with real measurements?
Yes. High voltage circuits need careful testing. Use proper instruments, safe procedures, and rated parts before final construction.