So is it the OT or the Circuit?

jh45gun · February 10th, 2008, 09:56 PM

Folks claim that a Fender amp can take a mismatch on the OT. Like if you have a 8 ohm tranny you can hook up an other cab for a 4 ohm load and be safe ect. So if that is so is it the OT they used or the circuit being able to handle it? Just wondering as my Clone has a 4 ohm tranny which is fine for running a 2x12 cab at 4 0hms but it seems like 4 ohm speakers are tough to find or expensive If I had one I would run it and I am afraid to run an 8 ohm by its self and maybe blow up the tranny. The Tranny is a Stancor Tranny. Just wondering as I have a two 8 ohm cabs running in parralel for 4 ohms so I am safe running as is. I was wondering if running a 8 single speaker would hurt it. I suspect it would cut down on the volume though which I do not want so I do not really plan on doing it. I was how ever curious as say I was playing and one speaker went if the mismatch would hurt the remaining speaker?

jh45gun · February 10th, 2008, 11:35 PM

To clarify my rambleing above, can you do the mismatch with any Tube OT (I always figured you should stay at what ever the ohm rateing was to be safe) or is this just a Fender thing?

peteb · February 10th, 2008, 11:48 PM

I do not know for sure but I think I remember that Marshall for instance is not as tolerant to a 1:2 OR 2:1 mismatch as a Fender. Marshalls have impedance choices on the amp, Fenders do not.

I always thought it strange that Fenders let you add another (extension) speaker in parallel that would cut the speaker load impedance in 1/2 and wondered if the tranny wasnt designed to have some where inbetween the single speaker load and the dual speaker load

on the other hand, isnt it OK to disconnect one speaker on a twin, or is it?

Dacious · February 11th, 2008, 12:33 AM

When you halve or double the impedance that is reflected all the way back into the amp. The reason you can do it is older Fender amps work their tubes pretty lightly. Marshalls tend to work them a lot harder so impedance mismatches are a little more likely to cause issues.

If you have a clone specced like an old Fender then you should be OK as long as your tubes are biased up right. You have to realise you are using the amp harder so a slighlty higher rate of wear on tubes and some longterm components like the OT is likely - but it won't catastrophically destroy anything.

If you drive it dimed with an mismatch and a overdrive in the front belting a really hot signal in you might have issues sooner rather than later.

jh45gun · February 11th, 2008, 12:51 AM

Thats good to know like I said I was just curious as I plan to keep the ohm rateing the same with no mismatch to be on the safe side. While a 4 ohm OT is kinda a pain as 4 ohm speakers are hard to find or expensive when you do find them running a 2x cab for a 4 ohm load is not that big of a deal.

Tim Swartz · February 11th, 2008, 08:07 AM

The Fender OTs apparently are over-spec'd to the point where the mismatch is not a big deal (other than a bit of power loss). Other OTs may or may not be as tolerant of a mismatch.

aztechmusic · February 11th, 2008, 08:39 AM

Hello,
I saw you question and thought I would leave a comment. As a rule of thumb you can always go up in your load from the rated OT. For instance if you have a 4 ohm OT, your optimum/best performing load should be 4 ohm. If you present
an 8 ohm load you will not hurt the transformer. Like you stated the sound power and tone will diminish because of the mismatch.

Where you can hurt the OT is when your load drops below it's rating. Should you drop the load to say 2 ohm or say you put an 8 with a 4 ohm load, it drops
to 3.2 something or there abouts, then you drop below the rating of the amp and you're in grey territory causing heat and a possible failure.

Hope this helps.

RomanS · February 11th, 2008, 09:13 AM

BTW, if you're looking for inexpensive 4 Ohm speakers, there's a 12" available in the Jensen Chicago series, don't know how good it is, though...

peteb · February 11th, 2008, 09:19 AM

Aztechmusic,

When you hook up an extension speaker in parallel like all fender amps are set up to do, aren't you cutting the speaker load in half?

jh45gun · February 11th, 2008, 11:45 AM

Thanks Roman I will check that out

peteb · February 11th, 2008, 12:00 PM

yes, I have the jensen RI C12N-4 ohm for my bassman head, good price at vintage speaker .com

works great for me

not sure what is meant by the Chicago series. THe Jensen reissues (no series) are meant to replicate regular jensen speakers from the 60s. I know weber has a Chicago series.

RomanS · February 11th, 2008, 02:11 PM

Quote:

Originally Posted by peteb

yes, I have the jensen RI C12N-4 ohm for my bassman head, good price at vintage speaker .com

works great for me

not sure what is meant by the Chicago series. THe Jensen reissues (no series) are meant to replicate regular jensen speakers from the 60s. I know weber has a Chicago series.

Maybe it's a regional marketing thing, but there's a series of Jensen speakers sold over here called "Chicago":
"The Jensen Chicago Series is a new design speaker line from Jensen using a half century experience of classic guitar speaker design and modern effective manufacturing technology."
- eg. here: http://www.tubeampdoctor.com/index.php?cPath=37_39_66

The one I was thinking about is called CH1270-4.

peteb · February 11th, 2008, 05:00 PM

http://www.vintagespeaker.com/search...ctmain=Speaker

these are the 12 inch Jensens vintage speaker.com

peteb · February 11th, 2008, 05:02 PM

RomanS I have never seen those

peteb · February 11th, 2008, 06:39 PM

the Chigago series looks to have smaller magnets and it says they are new

February 10th, 2008, 09:56 PM	#1 (permalink)
jh45gun Tele-Holic Join Date: Jan 2006 Posts: 981	So is it the OT or the Circuit? Folks claim that a Fender amp can take a mismatch on the OT. Like if you have a 8 ohm tranny you can hook up an other cab for a 4 ohm load and be safe ect. So if that is so is it the OT they used or the circuit being able to handle it? Just wondering as my Clone has a 4 ohm tranny which is fine for running a 2x12 cab at 4 0hms but it seems like 4 ohm speakers are tough to find or expensive If I had one I would run it and I am afraid to run an 8 ohm by its self and maybe blow up the tranny. The Tranny is a Stancor Tranny. Just wondering as I have a two 8 ohm cabs running in parralel for 4 ohms so I am safe running as is. I was wondering if running a 8 single speaker would hurt it. I suspect it would cut down on the volume though which I do not want so I do not really plan on doing it. I was how ever curious as say I was playing and one speaker went if the mismatch would hurt the remaining speaker? Last edited by jh45gun; February 10th, 2008 at 11:24 PM.

February 11th, 2008, 12:33 AM	#4 (permalink)
Dacious Friend of Leo's Join Date: Mar 2003 Location: Godzone Posts: 2,612 35 Photos	When you halve or double the impedance that is reflected all the way back into the amp. The reason you can do it is older Fender amps work their tubes pretty lightly. Marshalls tend to work them a lot harder so impedance mismatches are a little more likely to cause issues. If you have a clone specced like an old Fender then you should be OK as long as your tubes are biased up right. You have to realise you are using the amp harder so a slighlty higher rate of wear on tubes and some longterm components like the OT is likely - but it won't catastrophically destroy anything. If you drive it dimed with an mismatch and a overdrive in the front belting a really hot signal in you might have issues sooner rather than later. __________________ My other Telecaster is a Thinline The Tele Bible, Ch 1, v 10 Love thy Telecaster, covet not thy neighbour's Strat!

February 11th, 2008, 08:07 AM	#6 (permalink)
Tim Swartz Tele-Afflicted Join Date: Mar 2003 Location: Michigan - Tweenst the Great Lakes Posts: 1,821	The Fender OTs apparently are over-spec'd to the point where the mismatch is not a big deal (other than a bit of power loss). Other OTs may or may not be as tolerant of a mismatch. __________________

February 11th, 2008, 08:39 AM	#7 (permalink)
aztechmusic NEW MEMBER! Join Date: Feb 2008 Location: TN Posts: 2	You can go up but not down Hello, I saw you question and thought I would leave a comment. As a rule of thumb you can always go up in your load from the rated OT. For instance if you have a 4 ohm OT, your optimum/best performing load should be 4 ohm. If you present an 8 ohm load you will not hurt the transformer. Like you stated the sound power and tone will diminish because of the mismatch. Where you can hurt the OT is when your load drops below it's rating. Should you drop the load to say 2 ohm or say you put an 8 with a 4 ohm load, it drops to 3.2 something or there abouts, then you drop below the rating of the amp and you're in grey territory causing heat and a possible failure. Hope this helps.

February 11th, 2008, 09:13 AM	#8 (permalink)
RomanS Friend of Leo's Join Date: Jun 2006 Location: Vienna, Austria Age: 36 Posts: 2,710 14 Photos	BTW, if you're looking for inexpensive 4 Ohm speakers, there's a 12" available in the Jensen Chicago series, don't know how good it is, though... __________________ http://www.pbase.com/romans http://www.myspace.com/romans212

February 10th, 2008, 11:35 PM	#2 (permalink)
jh45gun Tele-Holic Join Date: Jan 2006 Posts: 981	To clarify my rambleing above, can you do the mismatch with any Tube OT (I always figured you should stay at what ever the ohm rateing was to be safe) or is this just a Fender thing?

February 10th, 2008, 11:48 PM	#3 (permalink)
peteb Tele-Meister Join Date: Apr 2003 Posts: 232	I do not know for sure but I think I remember that Marshall for instance is not as tolerant to a 1:2 OR 2:1 mismatch as a Fender. Marshalls have impedance choices on the amp, Fenders do not. I always thought it strange that Fenders let you add another (extension) speaker in parallel that would cut the speaker load impedance in 1/2 and wondered if the tranny wasnt designed to have some where inbetween the single speaker load and the dual speaker load on the other hand, isnt it OK to disconnect one speaker on a twin, or is it?

February 11th, 2008, 12:51 AM	#5 (permalink)
jh45gun Tele-Holic Join Date: Jan 2006 Posts: 981	Thats good to know like I said I was just curious as I plan to keep the ohm rateing the same with no mismatch to be on the safe side. While a 4 ohm OT is kinda a pain as 4 ohm speakers are hard to find or expensive when you do find them running a 2x cab for a 4 ohm load is not that big of a deal.

February 11th, 2008, 09:19 AM	#9 (permalink)
peteb Tele-Meister Join Date: Apr 2003 Posts: 232	Aztechmusic, When you hook up an extension speaker in parallel like all fender amps are set up to do, aren't you cutting the speaker load in half?

February 11th, 2008, 11:45 AM	#10 (permalink)
jh45gun Tele-Holic Join Date: Jan 2006 Posts: 981	Thanks Roman I will check that out

February 11th, 2008, 12:00 PM	#11 (permalink)
peteb Tele-Meister Join Date: Apr 2003 Posts: 232	yes, I have the jensen RI C12N-4 ohm for my bassman head, good price at vintage speaker .com works great for me not sure what is meant by the Chicago series. THe Jensen reissues (no series) are meant to replicate regular jensen speakers from the 60s. I know weber has a Chicago series.

February 11th, 2008, 05:00 PM	#13 (permalink)
peteb Tele-Meister Join Date: Apr 2003 Posts: 232	http://www.vintagespeaker.com/search...ctmain=Speaker these are the 12 inch Jensens vintage speaker.com

February 11th, 2008, 05:02 PM	#14 (permalink)
peteb Tele-Meister Join Date: Apr 2003 Posts: 232	RomanS I have never seen those

February 11th, 2008, 06:39 PM	#15 (permalink)
peteb Tele-Meister Join Date: Apr 2003 Posts: 232	the Chigago series looks to have smaller magnets and it says they are new