Dummy load headphone plug for the Crack

[Welderboy]

I'd like to make a dummy load headphone plug for my crack so I can burn in tubes without having the headphones plugged in.

Just wanted to confirm I have this right. Since the impedance on the HD650s is 300Ω and the crack Crack output 0.3W, all I need to do I solder 2x 150Ω 0.5W resistors as show below correct?

 

[Paul Birkeland]

You can run the Crack with no headphones plugged in and it will be loaded (heavily).

 

[Welderboy]

You can run the Crack with no headphones plugged in and it will be loaded (heavily).

Good to know! I have two new tubes coming in and they HD650s are loud enough that it's a bit of a bother.

Curious, do you know if the above approach would have work correctly? I already bought the plug so I might still make it to remind myself the amp is on and burning in.

 

[Paul Joppa]

The phones are 300 ohm per side, so 150 ohm resistors would match. Not that there's any problem with 150 ohms for a break-in load.

If you are breaking in an output capacitor, I think you would want a load so the cap carries some current. I have no evidence one way or the other that current through the cap is important for break-in load, but it is often claimed to be important.

 

[Paul Birkeland]

Curious, do you know if the above approach would have work correctly?

With no headphones plugged in, the output is shorted, which is a 0 ohm load (plus the ESR of the coupling cap plus its reactance at whatever frequencies might be playing through the amp).