Altec 802 permanent magnet
Field coil Conversion
Altec 802, 808 drivers permanent magnet to field coil conversion.
newest CH 802FC field coil drivers with the ultra pure iron nucleus,
and a special potted field coil, for inproved heat dissipation, with 7.5V dc at 2 Amps (warm
to the touch).
A variable regulated DC power supply capable of supplying up to 8V dc at 5A amps or more is recommended for both coils when operated in parallel.
They may be operated from 6V up to 7.75V DC
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.
For the ultimate in sound reproduction a field coil driver is unsurpassed !. Very musical, warm and smooth !
each: 10 Lbs.
Field Coil power consumption at recommended 7.5V 15W
High quality Teflon insuated, silver plated high temperature wire is used for all connections.
Shipped in one double box with an approximated weight of 22 Lbs. measuring 10 x 10 x 12 inches approximately
Prices. (per pair)
802 or 808 Type US $1390.00
Customer provides theit's own drivers, diaphragms must be in good working condition. New diaphragms at extra cost.
Conversion with drivers.
802 or 808 Type US $1965.00 includes new diaphragms from GPA, all aluminium, same as the original.
Shipping not included in the prices.
Shown in the graphic are the response curves of a CH802FC 7Vdc Field Coil converted 802 driver with 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:
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 7V 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 the higher frequencies.
This frequency response is rarely accomplished with the permanent magnet 802 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 7 and 8 Volts applied, only showing a relatively small increase of output at the frequency extremes at higher Voltages.
Measurements are taken at the throat of a converted driver with no horn at 1/24 octave spectra with a 16 Ohms diaphragm at 1 Watt (2.83 Volts RMS) sweep sinusoidal signal from 100HZ to 20,000 Hz., yielding a very high output well over 110db
No dividing network crossover was used.
The following graphic compares a unit before and after conversion with the recommended 7.5V dc applied to the field coil.
The red curve shows the response with the Field coil, the gray curve with the Alnico magnet.