Speaker advice for Silver Face Bassman

[revolver]

I've just acquired a mid-70's Bassman 100, which came with a slightly later (late 70's / early 80's) ported Bassman 115 cab.  The amp requires a 4ohm load, but the cab is 8ohm (I think it would originally have paired with the Bassman 135, which I believe had selectable impedance?)

 

The previous owner appears to have been using this combination for a good few years, but I've variously read that valve amps should be properly impedance matched, but also that Fenders are quite forgiving in that regard.

 

So my question is, should I be looking at getting a properly matched load at the earliest opportunity and, if so, is it worth trying to replace the existing speaker with an appropriate 4ohm equivalent?  Or has cabinet technology advanced so far in the last 45 years that I'd just be better off considering replacing the cab entirely?

 

Cheers! 

[ossyrocks]

Hi, 
 

Old Fender amps can tolerate an impedance mismatch very well. 100% either way is fine and you won't notice much difference in the way it performs.
Depending on your volume requirements, you could swap the speaker for something modern and more efficient (and much lighter), but it's worth checking what's in there already.

Personally, I would be looking at running the amp through a new cab. There are lots available now that would bring the best out of that amp.

 

Rob

 

[Bill Fitzmaurice]

14 hours ago, revolver said:

 Or has cabinet technology advanced so far in the last 45 years that I'd just be better off considering replacing the cab entirely?

 

Cabinet technology not so much, but driver technology for sure. You may be able to greatly increase performance replacing it. I can make recommendations knowing the exact internal dimensions of the cab and port. An 8 ohm cab is best, allowing you to use two should the need arise, although with a 100 watt amp it probably would not.

[revolver]

1 hour ago, Bill Fitzmaurice said:

Cabinet technology not so much, but driver technology for sure. You may be able to greatly increase performance replacing it. I can make recommendations knowing the exact internal dimensions of the cab and port. An 8 ohm cab is best, allowing you to use two should the need arise, although with a 100 watt amp it probably would not.

4 hours ago, ossyrocks said:

Hi, 
 

Old Fender amps can tolerate an impedance mismatch very well. 100% either way is fine and you won't notice much difference in the way it performs.
Depending on your volume requirements, you could swap the speaker for something modern and more efficient (and much lighter), but it's worth checking what's in there already.

Personally, I would be looking at running the amp through a new cab. There are lots available now that would bring the best out of that amp.

 

Rob

 

 

Many thanks both for the confirmation!

 

I forgot to mention that, yes the original speaker had already been swapped out for an 8ohm Celestion BN-15-300S (which might explain why the cab was a little lighter than I was expecting).

 

I'm not sure how to determine whether that speaker is suitable for the cab.  Based on these pictures from an eBay listing for the same model cab, the original speaker would have been a JBL 043091H.  

 

The internal dimensions of the cab are 62cm x 62cm x 32cm, and the oblong front-facing port measures 62cm x 3.5cm

 

Any suggestions greatly appreciated!

 

 

 

Edited 4 hours ago by revolver

[Bill Fitzmaurice]

The port depth is also required.

[revolver]

1 hour ago, Bill Fitzmaurice said:

The port depth is also required.

 

Ah, ok.  So the port extends 5.5cm to the inside edge of the baffle.  So like this in cross-section, if that helps?: