It is currently Mon Mar 16, 2020 7:13 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 10 posts ] 
Author Message
Post subject: '68 VM Vibrolux speakers?
Posted: Tue Apr 14, 2015 6:11 am
Offline
Amateur
Amateur
User avatar

Joined: Sun Aug 14, 2011 10:30 am
Posts: 174
I was just reading my '68 VM Vibrolux Reverb manual and realized it uses 2 8 ohm speakers for a 4 ohm load. I've been sometimes disconnecting the internal speakers and playing (at very low volume) the amp through different speakers that are 8 ohm . So, am I going to damage something if I do this? If I leave the internal speakers plugged in the internal jack, how about using 8 ohm extension speakers? I don't really get this stuff! Didn't the original '60's amps that had 2 speakers like the Vibrolux, Bandmaster, etc. have an 8 ohm load (I used to have have a Pro-Reverb back then)? Thanx!


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: '68 VM Vibrolux speakers?
Posted: Tue Apr 14, 2015 6:21 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
Redfarfisa wrote:
I was just reading my '68 VM Vibrolux Reverb manual and realized it uses 2 8 ohm speakers for a 4 ohm load. Like all vintage Fender 2 speaker amps

I've been sometimes disconnecting the internal speakers and playing (at very low volume) the amp through different speakers that are 8 ohm . So, am I going to damage something if I do this? No

If I leave the internal speakers plugged in the internal jack, how about using 8 ohm extension speakers? Your load will be 2.6 ohms , too low to be safe IMO

I don't really get this stuff! Didn't the original '60's amps that had 2 speakers like the Vibrolux, Bandmaster, etc. have an 8 ohm load (I used to have have a Pro-Reverb back then)?
2 X 8 oms speaker wire like Fender do = 4 ohms

Thanx!


Top
Profile
Post subject: Re: '68 VM Vibrolux speakers?
Posted: Tue Apr 14, 2015 9:52 am
Offline
Amateur
Amateur
User avatar

Joined: Sun Aug 14, 2011 10:30 am
Posts: 174
Thanks for the info! I gotta look this stuff up and figure it out. Way back when I was a kid I always played my Pro Reverb really loud with its own speakers and a Bandmaster cab plugged into the external speaker jack - so that would have been a 2 ohm load? It seemed like everybody did stuff like that all the time... 'course we blew a lot of speakers and amps back then, too :?


Top
Profile
Post subject: Re: '68 VM Vibrolux speakers?
Posted: Tue Apr 14, 2015 9:59 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
Redfarfisa wrote:
Thanks for the info! I gotta look this stuff up and figure it out. Way back when I was a kid I always played my Pro Reverb really loud with its own speakers and a Bandmaster cab plugged into the external speaker jack - so that would have been a 2 ohm load? It seemed like everybody did stuff like that all the time... 'course we blew a lot of speakers and amps back then, too :?


I frequently played a Fender amp under-loaded with an extension cabinet back then, usually at insanely loud volume levels. Never blew a speaker, a tube, or a tranny.

Of course, the amps back then were built a bit more stoutly than today......

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: '68 VM Vibrolux speakers?
Posted: Tue Apr 14, 2015 8:10 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Blowing the speakers ----> no speaker load on amp ----> blown amp. It's not a reasonable impedance mismatch that blows an amp, it's using the amp with no speaker connected (blown speakers). :wink:

2.6 ohm speaker load on a 4 ohm amp is perfectly fine. :idea:

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: '68 VM Vibrolux speakers?
Posted: Wed Apr 15, 2015 4:11 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
I am bothered to answer a question whose answer the operated amplifier beyond the recommendations of the manufacturer.


Top
Profile
Post subject: Re: '68 VM Vibrolux speakers?
Posted: Wed Apr 15, 2015 2:06 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Impedance matching is not a recommendation, it's a statement of getting rated power from the amp. Sometimes the statement is misconstrued, even by the ones who write the manuals. Most people simply don't understand what impedance matching is all about, and naturally that leads to the fear of the unknown. :wink:

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: '68 VM Vibrolux speakers?
Posted: Fri Apr 24, 2015 4:02 pm
Offline
Amateur
Amateur

Joined: Mon Jul 16, 2007 7:28 pm
Posts: 126
2.67 ohms would be too low for an amp wanting to see 8 ohms. The rule-of-thumb for a robust amp like a Fender is a mis-match by double (8 ohms for a 4 ohm amp), or half (2 ohms for a 4 ohm amp) is acceptable.
The internal speakers are now hooked up in parallel, so 2 x 8 ohms = 4 ohms total. If you re-did the wiring to put the speakers in series, you'd have 16 ohms, which paralleled with 8 ohms would yield 5.33 ohms total.
Try both and find out which sounds best. Mismatches change the sound. Only your ear can determine if the change is good.
Be aware that a mismatch in either direction will wear the power tubes out faster.
You pays your money, you takes your chances.
Be sure to report your findings here.


Top
Profile
Post subject: Re: '68 VM Vibrolux speakers?
Posted: Fri Apr 24, 2015 7:16 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
evets618 wrote:
2.67 ohms would be too low for an amp wanting to see 8 ohms. The rule-of-thumb for a robust amp like a Fender is a mis-match by double (8 ohms for a 4 ohm amp), or half (2 ohms for a 4 ohm amp) is acceptable...


This amp "wants to see" 4 ohms, so as you correctly pointed out, 2.66 ohms would be fine for this amp, within the acceptable 2 to 1 ratio. :wink:

evets618 wrote:
...Be aware that a mismatch in either direction will wear the power tubes out faster...


This is simply not true. In fact, with an acceptable impedance mismatch, the amp will put out less power, which could result in longer tube life. :idea:

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: '68 VM Vibrolux speakers?
Posted: Fri Apr 24, 2015 11:00 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
shimmilou wrote:
evets618 wrote:
...Be aware that a mismatch in either direction will wear the power tubes out faster...


This is simply not true. In fact, with an acceptable impedance mismatch, the amp will put out less power, which could result in longer tube life. :idea:


+1

The only scenario under which that assertion would be true is if the output stage was operating as a direct-coupled device, ie: no output tranny. One of a transformer's secondary functions is to act as a buffer, preventing such surges.

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 10 posts ] 

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: