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66 blackface bassman impedance?

That amp had an 125A13A output transformer. The output impedance is 4 ohms. There are two jacks on the back that are wired in parallel.

For optimal performance, you would normally plug in a single 4 ohm cab, or two 8 ohm cabs, one into each jack. That doesn't stop folks from plugging in a single 8 ohm cab.
 
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i have an Ampeg pn410 @8ohms that i got to match with an svt6pro...... but i wanted to plug the bassman into to see how it sounds as the original bassman cab i got with head has blown speakers and works but sounds horrible. i have no other cabs to plug it into for testing ..........just dont want to damage new pn410 or bassman head...........will it be safe?????
 
Most any bassman, but especially a blackface, is well worth putting money into and hanging on to. They're one of the classic amps.

Those were all really sturdy amps. I've played a bunch on 8 ohm cabs and never broke one, but they're really made for 4 ohms.
 
Keeping an amp in good working condition is not a negative thing on the vintage market. In general, this includes a power supply recap, a three conductor power cord, tubes, or anything else needed to make it useable. Keep the old parts.
 
okay, well i plugged in the 66 bassman and there is a few minor crackles and pops but all in all, it sounds really good.......like a vintage tube should.......its plugged into the 8ohm pn410 and is pretty loud for a 50 watt amp......pretty sweet for not being used for 20 years.
would it be louder if i had a 4ohm cab? ..........or i guess i could add another 8ohm cab and bring it down to 4.