> Tom, what does this paint can dummy load do In ham radio?

The dummy load presents a resisive load to the transmitter output.  The mineral oil for the can acts as a radiator to dissipate heat.
Back when dinosaurs roamed the earth, this was a perfectly useful dummy load.

Tom couldn’t change a battery in a $5 transistor radio.

wrote:

Can you cook with it?

You can with a long stick, a hot dog and an AM broadcast transmitter antenna.   A dry stick.

SamplesBoi wrote:

Alphas have one of these.

https://www.bkprecision.com/products/dc … /HVL600300

gemini for the win
An RF dummy load is designed for flat resistive impedance across megahertz frequencies to protect transmitters. While it presents a safe electrical load to a tube amp (preventing output transformer failure), driving a pure resistive load strips away the dynamic response of a real speaker cab, resulting in a flat, dark, compressed tone.

unless I want a flatt compressed tone

Then there's this:
Building a DIY reactive load box requires creating an $LCR$ (Inductance-Capacitance-Resistance) filter network that safely dissipates your tube amplifier's output wattage while emulating a real guitar speaker driver's frequency-dependent impedance curve ($Z$).

A standard 8Ω guitar cabinet exhibits two primary impedance spikes: a low-end mechanical resonance near 80 Hz–100 Hz (where impedance spikes to 30Ω–50Ω) and a high-end inductive rise starting around 1 kHz–2 kHz (where voice coil inductance $L$ causes impedance to climb toward 20Ω–30Ω at 10 kHz).

                      +---[ L1: High-Freq Inductor (~1.0 mH - 1.5 mH) ]---+
                      |                                                    |
[Amp Output Hot] ----+---[ R1: Primary Load Resistor (8 Ohm / 100W+) ]---+---- [Ground]
                      |                                                    |
                      +---[ L2: Low-Freq Inductor (~10 mH - 15 mH) ]-------+
                      |                                                    |
                      +---[ C1: Low-Freq Capacitor (~220 uF - 330 uF) ]----+
                      |                                                    |
                      +---[ R2: Damping Resistor (~22 Ohm - 47 Ohm) ]------+
Step-by-Step Circuit Design (8Ω / 100W Rating)
1. Primary Load Resistor ($R_1$)
* Spec: 8Ω total resistance, rated for at least 100W–150W (preferably non-inductive aluminum-housed power resistors mounted to a large heatsink).

* Function: Handles ~80–90% of the raw dissipated thermal energy.

2. High-Frequency Inductive Rise Network ($L_1$)
* Spec: 1.0 mH to 1.5 mH air-core inductor (14 AWG or 16 AWG speaker crossover inductor to handle high current without magnetic core saturation).

* Function: At low frequencies, the inductor presents minimal resistance. As frequency rises above 1 kHz, its inductive reactance ($X_L = 2\pi f L$) increases, adding impedance across the load and restoring top-end chime and pick attack clarity to the tube power section.

3. Low-Frequency Resonant Peak Network ($L_2 + C_1 + R_2$)
* Spec:

    * $L_2$: 10 mH to 15 mH inductor (Iron-core or air-core crossover inductor rated for high current).

    * $C_1$: 220 µF to 330 µF non-polar (bipolar) electrolytic capacitor (rated for at least 100V AC / 250V DC).

    * $R_2$: 22Ω to 47Ω / 25W power resistor.

* Function: Arranged as a series $LCR$ resonant tank tuned to $f_0 = \frac{1}{2\pi\sqrt{LC}} \approx 80\text{ Hz - 90\text{ Hz}}$. At resonance, the circuit branch presents an impedance spike that mirrors the physical cone resonance of a $12"$ speaker cabinet. $R_2$ damps the peak so the impedance spike remains within a safe 30Ω–40Ω range.

Adding a Safe, Variable Line-Out Tap
To capture a line-level signal for a recording interface or IR loader, place a high-impedance voltage divider in parallel with the main load:

[Main Load Hot] ---[ 10k Ohm / 1W Resistor ]---+--- [ Line Out Center Pin ]
                                               |
                                     [ 1k Ohm Potentiometer ] (Level Control)
                                               |
[Main Load GND] -------------------------------+--- [ Line Out Sleeve / GND ]
Critical Component & Safety Specifications
* Thermal Management: Mount all aluminum-housed power resistors to an extruded aluminum enclosure using thermal grease. Forced-air cooling (a 12V DC fan powered by a wall adapter or auxiliary circuit) is highly recommended for amps above 30W.

* Component Voltage Ratings: Use high-current audio speaker crossover inductors and non-polar capacitors rated for at least 100V to prevent dielectric breakdown under full power-tube overdrive.

* Continuous Wattage Headroom: Always double your amp's nominal output rating when selecting resistor power dissipation capacity (e.g., a cranked 50W EL34 head in heavy power-stage clipping can output peak bursts of 80W–90W).