Jump to content
Why become a member? ×

Using a valve amp with a 6 ohm cabinet


bumnote
 Share

Recommended Posts

Use 8 ohms, as it's better (in general...) to be presenting slightly less impedance. It's a nominal impedance anyway, and not really as critical as all that. What amp/cab..? That might help more than simply the impedance.

Edited by Dad3353
Link to comment
Share on other sites

[quote name='Dad3353' timestamp='1418335424' post='2629392']
Use 8 ohms, as it's better (in general...) to be presenting slightly less impedance. It's a nominal impedance anyway, and not really as critical as all that. What amp/cab..? That might help more than simply the impedance.
[/quote]

the cab is a pjb 12b and a fender 100t

Link to comment
Share on other sites

Some amps say "Minimum X Ohms" on the speaker outputs, so as long the cab is higher than X you are fine. Others just say "X ohms" which is a nominal rating - i.e. in that ball park will be OK, impedance change with frequency anyway.

I [i]think [/i]SS amps work the opposite way to valve amps though in whether they prefer cabs to be above or below the nominal rating - but don't quote me on that!

Link to comment
Share on other sites

[quote name='bumnote' timestamp='1418366427' post='2629539']
the cab is a pjb 12b and a fender 100t
[/quote]

In that case, I'd confirm the propos; Fender o/p trannies are usual happy at up to 100% 'mis-match', ie: 8 Ohm cab on 4 Ohm setting, 2 Ohm cab on 4 Ohm setting etc. 6 Ohms presented to the 8 Ohm setting won't hurt it. That's a great cab and a great amp; it'll sound wonderful, I'm sure. Nice gear. :)[size=4] [/size]

Link to comment
Share on other sites

[quote name='Dad3353' timestamp='1418397978' post='2629912']
In that case, I'd confirm the propos; Fender o/p trannies are usual happy at up to 100% 'mis-match', ie: 8 Ohm cab on 4 Ohm setting, 2 Ohm cab on 4 Ohm setting etc. 6 Ohms presented to the 8 Ohm setting won't hurt it. That's a great cab and a great amp; it'll sound wonderful, I'm sure. Nice gear. :)
[/quote]

Why thank you sir, will see how it sounds tonight

Link to comment
Share on other sites

I've a vintage Fender Bassman Export 50, which also gives off quite some heat on a sustained night. No fans in these old ones; check if yours is running, and make sure that there's adequate ventilation all around (nothing near the ventilation grills...). As long as it's not up to egg-frying temperatures, just very warm to the touch, I'd say it's OK. Be prudent, though, and check now and again.

Link to comment
Share on other sites

[quote name='Dan Dare' timestamp='1419276109' post='2638297']
Agree with Fender. Valve amps happy to work into a higher impedance, but less so into lower. Impedance of any speaker is far from fixed - it's frequency dependant and varies a lot (typical 8 ohm cab will vary between something like 6-80).
[/quote]

Personally, I'd maintain the opposite, but if Fender say it's OK, I suppose they should know.
As a general rule, valve amps (with O/P transformers...) work the opposite way to SS amps. For SS, too low an impedance (2 Ohms presented to a 4 Ohm amp...) could lead to damage (magic smoke...), but an open circuit (no load, so infinite impedance...) won't hurt it. Valve amps are the opposite. Too low impedance (up to 50%, as a general rule, or even a short circuit...) won't harm it, but an open circuit (no load, infinite impedance...) will generally end swiftly in damage (magic smoke...).
In your case, however, I'd follow Fender's recommendation, even though I don't understand their reasoning.

Edited by Dad3353
Link to comment
Share on other sites

[quote name='Dad3353' timestamp='1419277164' post='2638320']
Personally, I'd maintain the opposite, but if Fender say it's OK, I suppose they should know.
As a general rule, valve amps (with O/P transformers...) work the opposite way to SS amps. For SS, too low an impedance (2 Ohms presented to a 4 Ohm amp...) could lead to damage (magic smoke...), but an open circuit (no load, so infinite impedance...) won't hurt it. Valve amps are the opposite. Too low impedance (up to 50%, as a general rule, or even a short circuit...) won't harm it, but an open circuit (no load, infinite impedance...) will generally end swiftly in damage (magic smoke...).
In your case, however, I'd follow Fender's recommendation, even though I don't understand their reasoning.
[/quote]

Agree with Dad on this one.

Link to comment
Share on other sites

I think either would be OK, ive generally heard that a lower impedence setting ( 4 rather than 8 in this case) is better but im far from clear about the details of this, however i think that using either would wear out the power valves more quickly, when compared to using a more accurate nominal impedance amp and cab.

Link to comment
Share on other sites

  • 2 weeks later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...