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In Reply to: RE: if money wasn't a consideration... posted by Mr_Steady on November 30, 2014 at 05:04:58
I will make a mechanical analogy which may help you understand this topic a little bit.Voltage can be compared to speed, and current to torque, and an output trabsformer and a transmission have about the same job.
Putting a 32 ohm load on a 16 ohm tap is like trying to drive 80 miles an hour in 3rd gear. Yes it could work but you will run out of RPM(voltage). The whole intention of the output trabsforner is to match the tubes to the load, and the value is purely arbitrary provided the load and source have the same value (be it 4,8, 15(UK), 16, etc)
4,8,16 ohm etc speakers exist becasuse in the early history of radio it was decided that 2,000 ohm speakers are cumbersome and it's better to have a trabsformer and a practical to make voice coil.
The only reason 16 ohms is preferable on. Tube amp is when you either have a tapped secondary and 16 ohms is the only way to use all of it, or with an OTL amplifier, which is very limited in terms of current delivery (I.e. Already mismatched) and can usually make more power into higher impedance loads.
Edits: 11/30/14 11/30/14Follow Ups:
Hi Max,
First you are right about a higher impedence does not result in more power out of a tube amp. Klyle I hope you are reading this.
OTOH,
I finally remembered why higher speaker impedences are better for SET tube amps. It's because an OPT is an impedence matching device that steps down the impedence to a speaker level impedence. Of course it also transforms high voltage low current to low voltage high current.
I have read several places that running higher impedences extends tube life.
Now the following quote is the evidence I found to back up my argument. The link below is the cite. It even uses your powertrain analogy.
"Basically, and OPT is like an electronic gear box to couple a high revving engine with low torque
to slow turning wheels with high torque which is the case when we drive up the hill with truck
load of bricks. There are limits on the rev range, and the engine has bandwidth, like the OPT.
Now there is an odd thing about the load of bricks. The more bricks on the truck, the harder it
is to make it up the hill. But in electronics, the more ohms there are, the easier it is to sustain a
voltage across the load. That's because when you have less ohms, there is more current, because
Ohm's Law says that I = E / R, so with more current there is more power required.
So more ohms are easier to drive than a few ohms."
Now if you say, "We all know that," then I am going to feel ill, because it's what I've been trying to get across for a while. It's one of the reasons I was interested in 32ohms in the first place.
As an aside, I have Radiohead, "The Bends" on right now and it is coming on hard with the horns and SETs. Love it.
Jamie
Big speakers and little amps blew my mind!
Hi Jamie,I have two comments on the above analogy
1. consider that this analogy avoids one fact
Volts = speed of truck
Amps = weight of load
Ohms = height of hillPlay with the three variables and you will see Nothing is to be gained by changing
One, as they all depend on each other if the same amount of work is to be performed. (Power over a period of time)If joe can carry four cement blocks to the top of a 10 foot hill in the same time it takes steve to carry two blocks up a 20 foot hill, is there any difference in how much work the two guys did?
2. Yes using any device as less than its rated capacity may extend it's life, but then why not just use a smaller one, you aren't getting very good value.
3. Radiohead was the first album I played through my 2A3 amplifier - really brings them to life!
Edits: 12/01/14
"Putting a 32 ohm load on a 16 ohm tap is like trying to drive 80 miles an hour in 3rd gear."
Okay, forget I ever said that. I'm not going to do that.
If I try series it will be breaking up the four into two pairs, in series, at 16ohms. I will run it off the 16ohm tap of my OPT. I would need one stereo amp for each of the two horns. That is, one output tube per 16ohm pair.
I've been reading up on the resonant frequency issue.
More importantly I finally remembered the technical argument for the higher impedence, like 16ohms. I want to research it a little more, before I get into deep water with you. :)
Thanks for all your help.
Jamie
Big speakers and little amps blew my mind!
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