There are a variety of FC drivers requiring different voltages to energize the coils. Vintage RCA cinema drivers for example use 13.8VDC and 115VDC, average power consumption would be in the range of 20W.
There are a number of modern FR drivers that have field coils (Feastrex IIRC offers one) and conversions of certain old Altec models are also available.
FWIW I think using FC drivers warrants separate FC power supplies, and my preference for safety reasons would be for ones that operate on 12 - 16V.
Note that it is alleged that driving the VC of an FC driver without the FC energized is a potential way to fry the VC. Not convinced that that is at all the case, but my experience is very limited and only to the RCA drivers mentioned. (13.8V versions)
There are a number of modern FR drivers that have field coils (Feastrex IIRC offers one) and conversions of certain old Altec models are also available.
FWIW I think using FC drivers warrants separate FC power supplies, and my preference for safety reasons would be for ones that operate on 12 - 16V.
Note that it is alleged that driving the VC of an FC driver without the FC energized is a potential way to fry the VC. Not convinced that that is at all the case, but my experience is very limited and only to the RCA drivers mentioned. (13.8V versions)
In most cases the old field coils were wired in series with the rest of the amplifier load and provided the L in the typical CLC supply filter of the time. The voltage drop across the FC would have been less than 100V in most cases.
Modern performance requirements IMHO make this approach undesirable from a safety standpoint, and also a performance standpoint. (Hum) I'd use dedicated FC supplies. This is something I am more than a little interested in myself.
Hi,
I would recommend a SS constant current supply. The reason is that it is current, not voltage that builds the field up and since the resistance of the coil changes as it gets heated up so will the current if a constant voltage supply is used. I use this on my Feastrex and have never looked back
and the original Festrex supply is also of trhis type since a while back.
//Anders
I would recommend a SS constant current supply. The reason is that it is current, not voltage that builds the field up and since the resistance of the coil changes as it gets heated up so will the current if a constant voltage supply is used. I use this on my Feastrex and have never looked back
and the original Festrex supply is also of trhis type since a while back.//Anders
The field coil was used as the L in the power supply filter as mentioned. That was before good magnets became available. The current through the field coil was small by today's standards. You can use a fixed voltage supply as the easiest solution. A constant current source is much better. If you use an adjustable current source you can monitor the voltage across the magnet coil. If the voltage starts to rise it means the coil is heating up and when you get about a 25% increase from cold you probably are close to the original design current. Any more rise and you risk burning out the coil.
The simplest current source would be a high voltage (100 volts should do) and an adjustable power resistor. I would start with .01 amp and slowly increase the current. Of course once you decide on an operating point you could then measure the voltage and use a fixed voltage supply equal to the operating voltage.
The simplest current source would be a high voltage (100 volts should do) and an adjustable power resistor. I would start with .01 amp and slowly increase the current. Of course once you decide on an operating point you could then measure the voltage and use a fixed voltage supply equal to the operating voltage.
Feastrex
Gentlemen,
If this crowd can afford Feastrex drivers, I must be with the wrong group.
I doubt I could afford the admission cost to just listen to them, on my retirement income!
Please, let's bring the discussion down to an affordable level.
Is the advent of low voltage fieldcoils a recent development?
Which of the older drivers are preferable?
Gentlemen,
If this crowd can afford Feastrex drivers, I must be with the wrong group.
I doubt I could afford the admission cost to just listen to them, on my retirement income!
Please, let's bring the discussion down to an affordable level.
Is the advent of low voltage fieldcoils a recent development?
Which of the older drivers are preferable?
I can't afford any of the aforementioned drivers myself, and no, low voltage field coils are not a recent development - RCA was using them back in the 1930s for cinema sound.
FWIW based on your comments you might be better off looking for a nice set of alnico drivers, modern FC drivers are not affordable - for you the FC proposition would virtually have to be DIY to stay within your limited budget constraints. Very few vintage FC drivers as found in radios and phonographs prior to the 1940s are going to be worth the trouble sonically speaking.
You might identify some drivers that could be converted. The original magnets could provide the rough dimensions for a bobbin and magnetic structure.. I believe there may be people here who have or are in the process of doing it.
Field Coil PS
Kevin,
Thanks for your input.
I'm not destitute (yet) but $thousands for a driver seems too high.
Please list the "very few" vintage FC drivers that you consider worthwhile.
Is there a site for those dedicated enough to wind their own?
I understand from other threads that a PC power supply can be used instead of a battery.
Should FC drivers have independent PS?
Frank
Kevin,
Thanks for your input.
I'm not destitute (yet) but $thousands for a driver seems too high.
Please list the "very few" vintage FC drivers that you consider worthwhile.
Is there a site for those dedicated enough to wind their own?
I understand from other threads that a PC power supply can be used instead of a battery.
Should FC drivers have independent PS?
Frank
You can achieve very high flux densities at the penalty of significant heat, and you can change BL and some other ts parameters by varying the current into the FC. Claims have been made for lower distortion, but I don't know...
I have heard a few vintage RCA and some modern FC (model numbers do not come to mind - casual listening) and they can sound good. Not something I am about to entertain due to the cost and additional system complexity. It is so far outside of the realm of practical for me I have not devoted much effort on it.
Given my limited exposure I can't decide if there are real benefits in an era of neodymium, alnico and ferrite PMs, listening hasn't been conclusive for me although it demonstrates it is viable and not obviously inferior either.
I guess not running with the pack, the challenge of getting the technology to work well, and fun are as good a reason as any if the resources are available to do it well.
I have heard a few vintage RCA and some modern FC (model numbers do not come to mind - casual listening) and they can sound good. Not something I am about to entertain due to the cost and additional system complexity. It is so far outside of the realm of practical for me I have not devoted much effort on it.
Given my limited exposure I can't decide if there are real benefits in an era of neodymium, alnico and ferrite PMs, listening hasn't been conclusive for me although it demonstrates it is viable and not obviously inferior either.
I guess not running with the pack, the challenge of getting the technology to work well, and fun are as good a reason as any if the resources are available to do it well.
No specific recommendations, but most decent HP/Agilent supplies will do the job fine.. (Lots of others too, provided they have options for constant voltage or constant current operation.)
There is a bit of a craze currently (in China and Japan and to a lesser extent, here) for tungar bulb based full wave CT supplies with choke input and a single large electrolytic on the output. These are wildly inefficient, but seem to work OK in my limited exposure.
A cheap route to this is to wind the filament windings for the tungar bulbs on a large antec toroid using doubled up 14ga wire. The low voltage center tapped transformer connected to the plates should be driven by a variac to provide voltage adjustment.
The above is an over the top approach that works, but I can't vouch for the long term reliability and it is not very green to burn 100W of filament power for a pair of tungars for a couple of amps at 13V or so..
Thanks. I think most power supply involving tubes are voltage regulated and also provide a large voltage out. I need PS within 18V.
seen many of these, for sale used, over the years.
Lambda -
https://yandex.com/images/search?text=lambda++power+supplies
If there is spec data for the speaker that identifies the current level then that is the design aim. If there is no data, and the speaker was part of some equipment, then you need to reverse engineer the B+ idle current flowing in the coil. You would be playing with fire I suggest by using a DC resistance rise technique.
The idle current, and the DC resistance (warmed), identify the max supply voltage, but best to use a CC supply, otherwise you change the BL product of the magnet, and hence the sensitivity of the speaker output with time.
The idle current, and the DC resistance (warmed), identify the max supply voltage, but best to use a CC supply, otherwise you change the BL product of the magnet, and hence the sensitivity of the speaker output with time.
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