Altec 806 permanent magnet
Field coil Conversion
Altec 806 permanent magnet drivers conversion.
newest CH 806FC field coil drivers with the ultra pure iron nucleus,
an special field coil, will work very satisfactorily
with 6.75V dc at 2.3 Amps with low heat generation (warm
to the touch). A
variable regulated DC power supply capable of supplying up to 7V
dc at 5A amps or
more will be fine for both coils when operated in parallel. They may be
operated from 6 up to 7V DC.
High quality Teflon insuated, silver plated high temperature wire is used for all connections.
For the ultimate in sound reproduction a field coil driver is unsurpassed !. Very musical, smooth and warm !
each: 8 Lbs.
Shipped in one double box with an approximated weight of 20 Lbs. measuring 10 x 10 x 12 inches approximately
Prices. (per pair)
Small format Type 806, 804 etc. US $1245.00
Customer provides the drivers, diaphragms must be in good working condition. New diaphragms at extra cost.
Small format Type 806, 804 US $1765.00 includes new diaphragms from GPA, all aluminium, same as the original.
Shipping not included in the prices.
The field coil is a rock solid stand alone coil (no bobbin is used in its construction), potted in the driver body with a special heat transfering epoxy for best heat dissipation, forming together with the central pole piece a solid unit.
Shown in the graphic are the response curves of a CH806FC 7Vdc Field Coil converted 806 driver with 2.5V, 5.0V,
6.0V, 7.0V and 9.0 Volts DC applied to the field coil. Comparative measurements taken at the throat of the driver very closed to the phase plug. Final frequency response will vary according to the load and frequency characteristics of the horn used.
Measurements taken with color identifying curves and the following field coil applied potentials:
Blue 9V For testing purposes, do not apply higher than 7V for continuous use.
The magnetic field strength is directly proportional to the power applied to the field coil up to saturation at which an increase of power to the field coil won't increase the strength of the magnetic field and all that extra energy will be wasted as heat. In this configuration the best compromise is at 6.75V Volts dc, keeping the heat generation at a minimum with a very flat and high efficiency output throughout the audio response of the driver, extending very well up to he higher frequencies.
This frequency response is rarely accomplished with the permanent magnet 806 driver.
The frequency response as shown in the graphic is very flat and smooth even using a 1/24 octave spectra instead of 1/3 as is usually measured for a smoother more forgiving curve.
The frequency response clearly deteriorating as the power to the coil is reduced specially at the top and bottom ends of the frequency spectrum as shown in the gray curve, the response is very similar with 6.5 and 7 Volts applied, only showing a relatively small increase of output at the frequency extremes at higher Voltages.
The following graphic compares a unit before and after conversion with the recommended 6.75V dc applied to the field coil.
The red curve shows the response with the Field coil, the gray curve with the Alnico magnet.
Measurements are taken at the throat of a converted driver with no horn at 1/24 octave spectra with an 16 Ohms diaphragm at 1 Watt (2.83 Volts RMS) sweep sinusoidal signal from 100HZ to 22,000 Hz., yielding a very high output well over 110db. No dividing network crossover was used.