Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: pbman1953 on December 01, 2023, 10:55:46 am

Title: Testing an 8 ohm amp with a 4 ohm speaker
Post by: pbman1953 on December 01, 2023, 10:55:46 am

Would it be ok to test an 8 ohm tube amp with a 4 ohm speaker with a low volume?

Title: Re: Testing an 8 ohm amp with a 4 ohm speaker
Post by: Latole on December 01, 2023, 12:58:54 pm

IMO it is ok for few minutes test.
More ?

Title: Re: Testing an 8 ohm amp with a 4 ohm speaker
Post by: pbman1953 on December 01, 2023, 01:11:10 pm

The amp is a Fender Studio bass that converted to a head. My Super twin head has a Mercury 4/8 OT so I could use the 4 ohm OT from the St


The amps are similar. I know someone that covered both so I'll ask if the OT from the ST will work in the SB

Title: Re: Testing an 8 ohm amp with a 4 ohm speaker
Post by: Latole on December 01, 2023, 03:59:22 pm

It is not what you ask before. :BangHead:

Title: Re: Testing an 8 ohm amp with a 4 ohm speaker
Post by: tubeswell on December 01, 2023, 04:14:35 pm

Won't do any harm.

Title: Re: Testing an 8 ohm amp with a 4 ohm speaker
Post by: pbman1953 on December 01, 2023, 07:42:07 pm

Worked like a charm!


The only issue I have is that the tubes are biased very cold, 9 watts each. I want to raise that . Will a 2.5k pot in series with a 1.5k 2w resistor to ground , be enough.. I'll attach that before the output match pot

Title: Re: Testing an 8 ohm amp with a 4 ohm speaker
Post by: pbman1953 on December 03, 2023, 09:55:03 am

After dialing it in, I needed a 1.7k 2w watt to replace the2.7.




Even though they were close, between the RCA and GE 12at7, the GE won.



The amp is super quiet and sounds great.




Thanks for the input!