A lot of variables here ----and points of view on this subject + arguments -- " but it works okay with MY equipment " etc .
4.5 ohms is the nominal impedance which varies over the audio frequency band so it could go lower .
Next quality of design of transformers come into play , then you have reflected load back into the primary impedance affecting it --its not recommended but some will ignore this advice .
OTOH you could buy a USA made Weber Z-Matcher used by guitarists but it isn't cheap and Weber are out of stock at the moment .
Also Hammond sell them.
This thread will probably generate a lot of views as some audio people think its okay and wont cause any problems but I will stick with tradition and personally don't recommend it.
4.5 ohms is the nominal impedance which varies over the audio frequency band so it could go lower .
Next quality of design of transformers come into play , then you have reflected load back into the primary impedance affecting it --its not recommended but some will ignore this advice .
OTOH you could buy a USA made Weber Z-Matcher used by guitarists but it isn't cheap and Weber are out of stock at the moment .
Also Hammond sell them.
This thread will probably generate a lot of views as some audio people think its okay and wont cause any problems but I will stick with tradition and personally don't recommend it.
Tube amps, unlike the transistor ones, need the load to be relatively matched. Especially the pentode amps like this Siemens. It's not just the matter of causing harm (which is somewhat possible indeed, but not necessarily so), but also of performance - having the reflected load 3.5 times lower than the intended one can and will cause ridiculous amount of distortion, output power loss and lots of other problems.
I wouldn't recommend it either.
I wouldn't recommend it either.
You could use a Triad VPT230 series transformer. Connect the primaries in series and connect that to the amplifier output, connect the secondaries in parallel and connect the speaker.
You could also run the speaker through a 10R resistor, it'll match it but waste power doing it.
You could also run the speaker through a 10R resistor, it'll match it but waste power doing it.
Sadly schematics shows only one output winding, labelled 15 ohm.
TC: Siemens 2000 16mm Sf V 6.7 tube amp - www.tube-classics.de
Only 3 possibilities:
1) use amp with a proper 16 ohm load, whether a single 16 ohm one or 2 x 8 ohm in series.
I guess you are into full range speakers
2) don´t know what Country are you in (I wonder why people ALWAYS omit that VERY IMPORTANT data 🙄 ) but you might replace transformers with same type but 4/8/16 ohm outputs.
3) or, depending on where you live, it might be better to have them rewound.
Two small (30-50VA) toroid transformers 230-115V (2:1ratio) will give you a 4x impedance.
Edit: place the toroids with primary to amp's output the 4ohm speaker on the secondary.
Edit: place the toroids with primary to amp's output the 4ohm speaker on the secondary.
The Speltz Zero Autoformer is an often-used solution to impedance mismatches. They do work, I can say firsthand, but they are not inexpensive.
The "ZERO" Audio Autoformer Speaker Impedance Multiplier by Dick Olsher
New Zeros
The "ZERO" Audio Autoformer Speaker Impedance Multiplier by Dick Olsher
New Zeros
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My amp is a tube amp and has a 4 and 8 Ohm speaker output.
My speakers have an impedance of 6 Ohms, and I have never noticed a difference in sound alternating between 4 or 8 ...
What's more, I built a voltage shunt to feed the subwoofers from the speaker output, and when I connect or disconnect the dedicated amplifier, there is no sonic difference either, only the subwoofers disappear.
What's more, the manufacturer's manual says that you probably connect the speakers to the different terminals, and choose the sound that I like the most.
The only serious problem in an output transformer amplifier is that it is not connected to the speakers, but in some cases, in amplifiers without feedback, I have read that this is not an instantaneous damage as is a short circuit in an SS amplifier. without protection.
Academia50 --your mismatched impedance is nowhere near as great as a difference of 15 ohms & 4.5 ohms .
Impedance varies depending on the frequency and can drop below the average impedance stated -
Why does the impedance of inductor change with frequency? | Physics Forums
and no matter how you minimize it the reflected load is a fact of life in physics - quote-
"the impedance load seen by the tube and output transformer is not constant , the frequency of the audio signal will vary over a wide range . The inductance in the windings will have a different impedance at different frequencies . At a certain frequency an 8 ohm load may have an impedance of 10 ohms or at low frequency an impedance of 4 ohms . This varying load impedance is REFLECTED BACK to the Primary ,so the tube , and output transformer MUST work into a varying impedance range".
No matter how many people try to dis this its a physical fact of life and I will stick with reality and TG posting the same.
Impedance varies depending on the frequency and can drop below the average impedance stated -
Why does the impedance of inductor change with frequency? | Physics Forums
and no matter how you minimize it the reflected load is a fact of life in physics - quote-
"the impedance load seen by the tube and output transformer is not constant , the frequency of the audio signal will vary over a wide range . The inductance in the windings will have a different impedance at different frequencies . At a certain frequency an 8 ohm load may have an impedance of 10 ohms or at low frequency an impedance of 4 ohms . This varying load impedance is REFLECTED BACK to the Primary ,so the tube , and output transformer MUST work into a varying impedance range".
No matter how many people try to dis this its a physical fact of life and I will stick with reality and TG posting the same.
The inductance in the windings doesn't matter for the reflected impedance ... or we would have noticed when measuring the power with a dummy load 😀 basic
The actual speakers themselves do have a variable impedance ... another story . But music is not a single variable frequency , so if you have bass and voice it doesn't matter if there is something at 20KHz .
This is the reality of music and hearing , no solid state amp either can't push the same power at high frequency if the impedance of the speaker is higher .
The actual speakers themselves do have a variable impedance ... another story . But music is not a single variable frequency , so if you have bass and voice it doesn't matter if there is something at 20KHz .
This is the reality of music and hearing , no solid state amp either can't push the same power at high frequency if the impedance of the speaker is higher .
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Where do you think the majority of power amplifiers output transformers are connected to ---? of course it not another story , as soon as you connect components in an electrical/electronic circuit like an audio amplifier you have electrical reactions that why D.Self employs a 100 pf comp.capacitor in his designs and JLH only used a 10pf or thereabouts to stabilize the designed circuit .
You cant isolate a whole design and just design it for just one section like the input or VAS it all goes together as a whole , likewise output transformers connect to loudspeakers even D.Self acknowledges that .
You cant isolate a whole design and just design it for just one section like the input or VAS it all goes together as a whole , likewise output transformers connect to loudspeakers even D.Self acknowledges that .
Thanks for the link.
I only wanted to contribute my two cents, but you are right, I hurried to write and did not see that difference in impedances, (quite large, by the way) maybe they are audible ...😉
This is a big story about how speakers are made and function , it is the same for solid state amplifiers ... has nothing to do with the original problem - matching a tube amplifier with a load .
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It's what I think, fixed resistors don't radiate sound, right? We are talking about whether there is any electronic/physical
damage to the OPT and its associated tubes ...
Will that be detrimental to the amp in the long run?
If that's a big concern for the OP, a dummy charge to make up the difference will not be audible and he will be quiet. I think.....
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The majority of music power is at low frequency , where speakers are like a dummy load .
The answer to your question is NO .
Like others have said , a tube amplifier will work with no issues with a different load , but with reduced output power and probably more distorsions at high output level .
The answer to your question is NO .
Like others have said , a tube amplifier will work with no issues with a different load , but with reduced output power and probably more distorsions at high output level .
For the OP:
I was thinking that you have probably turned to this forum thinking of an easy, cheap and efficient solution to your problem.
The following occurred to me, is what I would do if I wanted to be covered for fear of spoiling something in that pair of vintage monoblocks .....
Find two unused speakers, (8 ohms or 4 ohms, everything will do) and measure the DCR
(voice coil winding resistance with no signal, it's easy) and connect them in series to achieve the approximate impedance of 16 ohms you need to be calm.
For example:
Your speakers 4.5 ohms, you can add 8 + 4 ohms, 3 x 4, etc.
Take out the cones, cut them with a cutter, and you can hide them behind the amplifier being careful not to touch the terminals or any metal part of the amplifier. You can make small wooden boxes for them, look for prefabricated PVC boxes, put terminal blocks, etc.
You will have the final approximate you are looking for and there will be no audible effect whatsoever that impairs your hearing.
If you plan to listen at high volumes, try to get 4/6-inch speakers, if not, with small ones from old transistor radios or those cheap mini-speaker cabinets for PC will do.
Probably the overly theoretical ones here, but with little or no practical repair experience start with the typical theoretical ramblings and attach links about "what happens when you connect two speakers in series instead of parallel".
Ignore them.
I was thinking that you have probably turned to this forum thinking of an easy, cheap and efficient solution to your problem.
The following occurred to me, is what I would do if I wanted to be covered for fear of spoiling something in that pair of vintage monoblocks .....
Find two unused speakers, (8 ohms or 4 ohms, everything will do) and measure the DCR
(voice coil winding resistance with no signal, it's easy) and connect them in series to achieve the approximate impedance of 16 ohms you need to be calm.
For example:
Your speakers 4.5 ohms, you can add 8 + 4 ohms, 3 x 4, etc.
Take out the cones, cut them with a cutter, and you can hide them behind the amplifier being careful not to touch the terminals or any metal part of the amplifier. You can make small wooden boxes for them, look for prefabricated PVC boxes, put terminal blocks, etc.
You will have the final approximate you are looking for and there will be no audible effect whatsoever that impairs your hearing.
If you plan to listen at high volumes, try to get 4/6-inch speakers, if not, with small ones from old transistor radios or those cheap mini-speaker cabinets for PC will do.
Probably the overly theoretical ones here, but with little or no practical repair experience start with the typical theoretical ramblings and attach links about "what happens when you connect two speakers in series instead of parallel".
Ignore them.
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