Hi! I have a Wurlitzer 1400 Jukebox which uses a 514 tube amplifier. In addition to driving the internal 8ohm speaker, there is also a two-screw terminal strip to allow connection of external speakers. This output is labeled “Aux Speakers 500 ohm Line”. There is also a “fader” rotary switch that the manual explains allows the output to be balanced between the internal and aux speakers. The manual explains that the aux speakers should use line transformers to convert from the 500ohms to the individual speaker impedance.
I know that there are constant voltage speakers that are typically rated at 25, 70.7, or 100 volts. But there is no reference in the manual to constant voltage or any of these voltage levels. Does the 500 ohms imply one of these voltages, or is the 500 ohm output something completely different? I can find a lot of info about constant voltage speakers, but no references to 500 ohm outputs.
Thanks for any help!
-Steve.
I know that there are constant voltage speakers that are typically rated at 25, 70.7, or 100 volts. But there is no reference in the manual to constant voltage or any of these voltage levels. Does the 500 ohms imply one of these voltages, or is the 500 ohm output something completely different? I can find a lot of info about constant voltage speakers, but no references to 500 ohm outputs.
Thanks for any help!
-Steve.
Leaving aside your jukebox "100 volts line" speakers implies very long speaker lines that a normal power amp would have trouble driving .
Used in factories for example the principle is like your typical power station supply starts off at over 100,000 volts and steps down at local level via transformers .
This is to compensate for long line losses otherwise extremely thick cables would have to be used to lower power losses.
At each speaker is a "100 volt " line step-down transformer enabling many speakers to be attached ( 100 volts is UK spec. in the USA its limited to 70 volts although this is changing to 100 volts now).
The transformers in the remote speakers are rated in wattage NOT input impedance and the power amp is supplied with a 100 volt tap at the output.
I do not have the circuit diagram but what I described applies to LINE powered remote speaker systems if that old 1951 jukebox doesn't work that way and uses a different system then let me know.
I can only surmise the "500 ohms" applies to the loop resistance of the external cabling but I am open to offers ?
Fidelity is low !
Used in factories for example the principle is like your typical power station supply starts off at over 100,000 volts and steps down at local level via transformers .
This is to compensate for long line losses otherwise extremely thick cables would have to be used to lower power losses.
At each speaker is a "100 volt " line step-down transformer enabling many speakers to be attached ( 100 volts is UK spec. in the USA its limited to 70 volts although this is changing to 100 volts now).
The transformers in the remote speakers are rated in wattage NOT input impedance and the power amp is supplied with a 100 volt tap at the output.
I do not have the circuit diagram but what I described applies to LINE powered remote speaker systems if that old 1951 jukebox doesn't work that way and uses a different system then let me know.
I can only surmise the "500 ohms" applies to the loop resistance of the external cabling but I am open to offers ?
Fidelity is low !
Some organ amplifiers have 500R speaker winding.
As Duncan said, most likely to handle long wires and odd PA speakers.
Of course they also have more regular Hifi winding for 4R, 8R etc..
As Duncan said, most likely to handle long wires and odd PA speakers.
Of course they also have more regular Hifi winding for 4R, 8R etc..
Thanks - yup, I appreciate how the constant voltage system works and understand that there are various standards that have been used (100v, 70v, 25v), but I was wondering if my "500 ohm line" output necessarily corresponded to one of these standards (or perhaps some other pre-standard value).
I guess I could input a sine wave and crank the amp up to max and measure the Vrms output at these terminals with the fader set to different settings, but I was hoping that it would be obvious (to someone else!).
Oh, and I attached the schematic for the amp.
Thanks,
-Steve.
I guess I could input a sine wave and crank the amp up to max and measure the Vrms output at these terminals with the fader set to different settings, but I was hoping that it would be obvious (to someone else!).
Oh, and I attached the schematic for the amp.
Thanks,
-Steve.
Attachments
The impedance of a 5W speaker on a 100V line is 2,000 ohms.
The total impedance of four of these connected in parallel would be 500 ohms.
Impedance = voltage squared/power
The total impedance of four of these connected in parallel would be 500 ohms.
Impedance = voltage squared/power
Ah ! now that schematic explains it all this is "old school " working by that I mean early 1930,s tube radio working of which I have repaired 100,s of that type .
I have even now an original 1930,s extension house speaker using this method .
As the internal jukebox speaker is standard operation the external ones are FIELD-COIL speakers that means they are energized by a high voltage coil instead of a permanent magnet speaker while still retaining a low impedance voice coil.
Thanks Brice for the info on 500 ohm speaker winding's of organ amplifiers.
I have even now an original 1930,s extension house speaker using this method .
As the internal jukebox speaker is standard operation the external ones are FIELD-COIL speakers that means they are energized by a high voltage coil instead of a permanent magnet speaker while still retaining a low impedance voice coil.
Thanks Brice for the info on 500 ohm speaker winding's of organ amplifiers.
Got it Galu, but why are you assuming this is a 100v line? Seems we have too many unknowns in the equations.
Ok thanks - this is getting at the heart of my question. Seems that I need to either know the power or the voltage in addition to the 500 ohm impedance. I know the total power of the amp is about 25W, but some portion of that is used by the internal speaker. I can make some guesses/assumptions - and it's not likely to be an issue anyway because I'm not going to load up the aux with a bunch of high wattage speakers. It was more about being curious how someone would know how to apply the 500 ohm nomenclature.
I understand that as these constant voltage systems were standardized, one of the primary goals was to make it easy to make sure that the amp wasn't overloaded. If the output was rated at 70V and you knew the max wattage, then you could use 70V coupled speakers and just add up the wattage for each of the speakers and make sure the total was below the max. This was easier than adding up the parallel impedances.
500ohm outputs and constant voltage outputs like 25, 70, 100v do not go together easily.
But for certain wattage ranges there can be a match.
Ohm's law applies: P=V*V/Z
e.g. there is a good match for a 10W speaker: 70v*70v/500ohm=9.8W
That means if you hook up a 70v transformer with its 10W tap to your 500ohm output, you get an almost perfect match for a 10W line speaker.
Similarly you could hook up a 25v transformer on its 1.25W tap for 1.25W speaker output.
Both examples are valid for one line speaker only.
The 500 ohm output is not as flexible as the constant v when it comes to more than one speakers.
Say you have two 5W speakers to drive from 500 ohm, you could connect two 70 v transformers with their 5W taps in parallel. a.s.o.
But for certain wattage ranges there can be a match.
Ohm's law applies: P=V*V/Z
e.g. there is a good match for a 10W speaker: 70v*70v/500ohm=9.8W
That means if you hook up a 70v transformer with its 10W tap to your 500ohm output, you get an almost perfect match for a 10W line speaker.
Similarly you could hook up a 25v transformer on its 1.25W tap for 1.25W speaker output.
Both examples are valid for one line speaker only.
The 500 ohm output is not as flexible as the constant v when it comes to more than one speakers.
Say you have two 5W speakers to drive from 500 ohm, you could connect two 70 v transformers with their 5W taps in parallel. a.s.o.
Thanks! OK, so I'm getting that 1) my 500 ohm output is NOT the same thing as a constant voltage output, and 2) that I should make sure that there is a 500 ohms equivalent at the output by making sure I use the right combination of transformers, taps, and speaker wattages. For your first example with a single 10W speaker and a 70V transformer, does the speaker itself need to be rated at 10W or can I use a larger wattage speaker as long as I'm using the 10W transformer tap? Or does the speaker itself need to also be a 10W rated speaker?
Also, how does all of this work with the fader? Seems that would change things quite a bit. The manual says the Phono Only directs all power to the internal speaker; setting "A" results in 25% of the output to the aux speaker and 75% to the internal speaker; "B" results in a 50/50 split, and "C" results in 75% to the aux and 25% to the internal speaker. Wouldn't the setting of this fader switch change the equations here?
Also, how does all of this work with the fader? Seems that would change things quite a bit. The manual says the Phono Only directs all power to the internal speaker; setting "A" results in 25% of the output to the aux speaker and 75% to the internal speaker; "B" results in a 50/50 split, and "C" results in 75% to the aux and 25% to the internal speaker. Wouldn't the setting of this fader switch change the equations here?
P=V²/Z so with 500Ω and 20W (realistic with 6L6 PP) the output is √(20x500)=100V.
You can hook-up speakers with 100V line transformers up to 20W.
With 20W total speakers the amp sees a load of 500Ω.If the total is less then 20W the amp sees more and produce less power.With more then 20W speakers the amp is overloaded and produce also less power and the speakers get less then expected.
Mona
You can hook-up speakers with 100V line transformers up to 20W.
With 20W total speakers the amp sees a load of 500Ω.If the total is less then 20W the amp sees more and produce less power.With more then 20W speakers the amp is overloaded and produce also less power and the speakers get less then expected.
Mona
I think the transformer tap is probably for a 70 volt speaker. 70.7 squared gives 4998 and the industry says to round to 5000. Therefore 5000/500=10 watts or 10 (70 volt speakers tapped at 1 w each), or (2 speakers tapped at 5 watts each) or 1 speaker tapped at 10 watts.
The output is going to be either the 8 ohm or 4 ohm tap or the 500 ohm tap but not a combination of the 4,8, or 500 in most cases. However I too have seen instances where load A and load B can be used at the same time.
Generally one doesn't load an amplifier over 80% this is especially true with a SS amplifier. Tube amplifiers are more forgiving and generally will last when tapped at 100% but expect diminished output tube life.
The output is going to be either the 8 ohm or 4 ohm tap or the 500 ohm tap but not a combination of the 4,8, or 500 in most cases. However I too have seen instances where load A and load B can be used at the same time.
Generally one doesn't load an amplifier over 80% this is especially true with a SS amplifier. Tube amplifiers are more forgiving and generally will last when tapped at 100% but expect diminished output tube life.
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Thanks Burnedfingers - yeah, for this amp it uses a fader switch to select how much power goes to the internal 8ohm speaker and how much goes to the 500ohm out. The schematic is attached a few posts back. It's still not clear to me how all this is really supposed to work (see my post #12). The manual for this jukebox provides part numbers for line transformers that enable either 8 or 4 ohm external speakers, but doesn't provide any specs on them nor can I find any references to these part numbers on line (it's a 1952 jukebox). So, I don't really know what type of transformers they are.
It looks to me like its probably 70 volt transformers. Generally 25 volt are used in something like a school intercom system. So it lists several transformers one for a speaker with a 4 ohm voice coil and a different one for a speaker with a 8 ohm voice coil.
If your buying a 70 volt spk/transformer combination (all in one) then the speaker wattage is in line with the transformers maximum wattage. So a 10 watt transformer speaker combination would have a speaker rated for ten watts maximum. You can purchase commercial speakers on line and their quite cost effective just don't expect a lot of low end because generally a 8" 70 volt speaker is 3db down at 100 hz. They are to be blunt meant for background noise nothing spectacular.
I wouldn't loose any sleep over the control setting simply because it isn't critical. Get somewhere close and its ok.
If your buying a 70 volt spk/transformer combination (all in one) then the speaker wattage is in line with the transformers maximum wattage. So a 10 watt transformer speaker combination would have a speaker rated for ten watts maximum. You can purchase commercial speakers on line and their quite cost effective just don't expect a lot of low end because generally a 8" 70 volt speaker is 3db down at 100 hz. They are to be blunt meant for background noise nothing spectacular.
I wouldn't loose any sleep over the control setting simply because it isn't critical. Get somewhere close and its ok.
HI Steve,
Burnedfingers has it right, and you don't have to add up to 500 R either. It just allows you to hang an unknown number of speakers on the unit as long as the power taps added do not exceed the 10W you figured out. The main speaker still takes most of the power, so a variable load on the 500 R output won't drive the output section nuts. Keep in mind that 1 watt can be pretty loud with the typical full range loudspeaker. So try some 70 volt line transformers out.
If you want a better sound, use a higher power transformer (say 10 watts) for a low power output rather than using a 5 watt transformer set for 2.5 watts or something like that. I've designed a few large P-A systems and you can get a fair amount of sound out of a bunch of wall mounted full range speakers.
-Chris
Burnedfingers has it right, and you don't have to add up to 500 R either. It just allows you to hang an unknown number of speakers on the unit as long as the power taps added do not exceed the 10W you figured out. The main speaker still takes most of the power, so a variable load on the 500 R output won't drive the output section nuts. Keep in mind that 1 watt can be pretty loud with the typical full range loudspeaker. So try some 70 volt line transformers out.
If you want a better sound, use a higher power transformer (say 10 watts) for a low power output rather than using a 5 watt transformer set for 2.5 watts or something like that. I've designed a few large P-A systems and you can get a fair amount of sound out of a bunch of wall mounted full range speakers.
-Chris
The "70V" system evolved well after WWII, and jukeboxes were conservative designs.
The "500 Ohms" means you do math and compute power. ("70V" reduces this tough work.)
It *happens* that 20 Watts in 500r is 100V. So *for this amp* 100V transformers do the right thing. However in the USA we no longer run 100V lines casually, so the transformers are not stock items.
Do you have a VERY large dance-hall which needs 2W-5W speakers in every nook and cubby? Will you run the volume control ALL the way up? If not, just use up to 10 Watts of 70V transformer load, it will be fine.
The "500 Ohms" means you do math and compute power. ("70V" reduces this tough work.)
It *happens* that 20 Watts in 500r is 100V. So *for this amp* 100V transformers do the right thing. However in the USA we no longer run 100V lines casually, so the transformers are not stock items.
Do you have a VERY large dance-hall which needs 2W-5W speakers in every nook and cubby? Will you run the volume control ALL the way up? If not, just use up to 10 Watts of 70V transformer load, it will be fine.