Use 300b speaker amp as headphone amp?

[Dogen]

I have an old Assemblage 300B single-ended speaker amp I’m not using at the moment. Is there any way to use or adapt this amp to drive my Sennheiser 6xx headphones? It outputs at best 8 Watts per channel, and is currently wired for 8 ohm speakers.

I did some research and found the with a resistor or two it’s possible to adapt a solid state amp to drive cans. But, I saw vague warnings not to attempt this with tube amps - something about it’s not good for the output transformers.

This is all in the spirit of fun — don’t want to risk damage to the amp or the headphone.

 

[Blumlein 88]

I've done this on a different 300b. I loaded the output with some 10 ohm power resistors. The lack of a load on the transformer can cause those amps to oscillate. Then just made up a cable to go from amp to phones. So the phones are connected in parallel to the resistors and you don't mess up the output impedance.

Without knowing the gain of your amp it could be rather too much or just right. I was lucky and it was just right.

 

[Dogen]

I've done this on a different 300b. I loaded the output with some 10 ohm power resistors. The lack of a load on the transformer can cause those amps to oscillate. Then just made up a cable to go from amp to phones. So the phones are connected in parallel to the resistors and you don't mess up the output impedance.

Without knowing the gain of your amp it could be rather too much or just right. I was lucky and it was just right.

FWIW, the amp has a gain of 23dB. So, how did it sound?

 

[Blumlein 88]

FWIW, the amp has a gain of 23dB. So, how did it sound?

Sound was very nice. You'll like it.

23 db is probably too much. If yours has the volume control it will work, but you may have to keep volume rather low.

 

[Dogen]

Somewhere around here I have a pair of Rothwell inline attenuators, 6 or 10 dB I think. I could put those between the source and the amp. Is that the right idea?