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Topic: Paging Ken Fox |
Andrew Buhler
From:
Maryland, USA
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Posted 6 Mar 2005 3:41 pm |
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| Ken, I just picked up a nice 66 Vibrolux Reverb. For some reason, the previous owner intalled two 4 ohm speakers instead of two 8 ohm. Since the OT wants to see 4 ohms and not 2, will this (down) impedance mismatch damage the transformers? It seems that people on various forums have differing opinions. Many thanks! [This message was edited by Andrew Buhler on 06 March 2005 at 03:48 PM.] |
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Andy Zynda
From:
Wisconsin
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Posted 6 Mar 2005 3:51 pm
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100% this way or that will not harm the tranny. Especially if the direction is lower versus higher impedance. The only problame you'll have is that the output section wont be running at it's peak efficiency.
A bit of headroom lost, but not very much.
Vibroluxes sound **SWEET** with Weber P10N's in them.
https://weberspeakerscom.secure.powweb.com/weber/10a150.htm
To die for....
-andy-
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Andrew Buhler
From:
Maryland, USA
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Posted 6 Mar 2005 3:59 pm
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| Thanks Andy. The amp currenty has 10F150T 4 ohm Webers--sounds very nice. I think I would break down and cry if I fried the output transformer. Glad to know I can play the amp as is. |
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Jim Harper
From:
Comanche, Oklahoma, USA * R.I.P.
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Posted 6 Mar 2005 4:41 pm
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| I believe Ken did not leave Dallas til this morning. He is driving to Ga.==Jim Harper |
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Mike Wheeler
From:
Delaware, Ohio, USA
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Posted 6 Mar 2005 5:02 pm
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Hi Andrew,
As long as you're not driving the amp into distortion you shouldn't have any problems. If you push it real hard the OT can over-heat and the windings can short out.....not good.
If it were a classic vintage amp, I'd either replace the speakers with two 8 ohmers, or replace the OT with one that wants to see a 4 ohm load. (but I'm real picky about that stuff)
------------------
Every day is a Great day,
Mike
(aka Sideman)
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Jon Light (deceased)
From:
Saugerties, NY
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Posted 6 Mar 2005 5:12 pm
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As you say, Andrew, there are various opinions out there. I have run Fenders pretty hard at incorrect impedance--a Dual Showman Reverb driving an 8 ohm speaker--for many hours with no problem. But obviously running the correct impedance load is the best and safest answer. In addition to changing your speakers or changing your OT (not likely something you are eager to do), there is one more option----Weber makes an impedance matching unit for exactly this situation--
https://weberspeakerscom.secure.powweb.com/store/zmatch.htm
I have no experience with this product but I've read that it does what it's supposed to with no sonic degradation. Seems like a real option.
[This message was edited by Jon Light on 06 March 2005 at 05:13 PM.] |
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Bill Hatcher
From:
Atlanta Ga. USA
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Posted 6 Mar 2005 5:51 pm
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Not good to have a lower impedence speaker than the output tformer. You will have a loud amp for a shorter period of time. Voltage arcs will happen in the output tubes and the tformer will run hot as the mismatch forces lots of amperage through them. Something will give out over time, hopefully the output tubes and not the tformer.
I don't think that 4 into 2 ohms will kill the amp as much as say a mismatch of 8 into 2ohms, but you should disconnect one of the speakers. I have worked on several older Fender amps that had mismatched outputs and seem to run for years with no effect. Probably were not abused and just moderate levels of out put. |
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Bob Tuttle
From:
Republic, MO 65738
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Posted 6 Mar 2005 6:31 pm
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| If you have a 4 ohm output transformer and run an 8 ohm speaker load, you won't hurt anything. You'll just have less output. However, if you have a 4 ohm output transformer and run a 2 ohm speaker load, you could burn up something, sooner or later. |
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Andrew Buhler
From:
Maryland, USA
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Posted 6 Mar 2005 7:11 pm
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Thanks for all the advice. I think I am just going to hold tight until I have two 8 ohm speakers to throw into the amp. No need to take chances with an amp like this.
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Andy Zynda
From:
Wisconsin
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Posted 6 Mar 2005 9:45 pm
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Dont mean to be contrary Bill, but it's higher impedances that will cause voltage arcs. That's the reason that fender and almost all tube amps have shorting switched speaker output jacks. With the speaker unplugged, the output is shorted. This will cause a near zero ohm load. This load will reflect back to the primary windings, and will be "heavier" than the imedance between windings, plates to grids, etc. It's an "emergency safety load".
Open up that output, with nothing (infinite impedance) to load it down, and that very high impedance will reflect back to the primariy, and will be of higher impedance than the tube's elements and the primary windings. That's when arcing and shorts will occur, both in the output tubes, and between windings of the primary side of the output transformer.
-andy-
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Ken Fox
From:
Nashville GA USA
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Posted 8 Mar 2005 7:30 am
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Just got in from Dallas and back on the road today for Virginia. I think Andy and Bill covered this better than I could have! I really avoid a two ohm load, unless I have a Super Reverb output transformer!
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