Radford HD250

1 9 7 5 1975

A brand I know strictly nothing about except it was mainly known for its valve / tube amplifiers in the 1960s... but not its 1970s solid-state designs.

I just happened to have extra-rare leaflets for the HD250 and two other solid-state components which I sent to Paul Kemble - better visit his website for a serious study of the HD250.

Two Radford websites seem to coexist today : radfordaudio.co.uk and the Arthur Radford Appreciation Society, plus the Yahoo discussion group.

Wikipedia also has a somewhat slanted but detailed page, at least regarding the early and late lives of Radford - the 1970s seem to remain so far a bit... in the dark ?

Radford HD250, image 1 Radford HD250, image 2
Radford HD250 specifications
Title Value
Rated output : 2x 50W (both channels driven, 4...8 Ohm load)
Maximum output : 2x 90W (5 Ohm load)
Recommended load impedance : 8 Ohm nominal
Output source impedance : 0,1 OHm in series with 2200µF and 2µH
Rated sensitivity : 2mV at 1Khz, RIAA equalized (phono ; for rated output ; 1V / 0dBv at pre-out)
100mV, flat response (lines ; for rated output ; 1V / 0dBv at pre-out)
Overload margin : 40dB minimum (phono)
35dB minimum (lines)
18V RMS (= +25dBv ; line output at clipping level ; power-amp in disconnected)
Frequency response : ± 0,2dB RIAA (typical)
± 0,5dB RIAA (with 12dB/octave LPF, -3dB @ 30Hz)
20Hz...32Khz (-1dB, lines)
Bass control : ± 11dB @ 30Hz
Treble control : ± 12dB @ 20Khz
Rise time : 6µs (for rated output, tone controls off)
Input impedance : 47kOhm (phono)
27kOhm nominal (lines)
Hum & noise output : -80dBv (phono, 2mV input, standard A-weighted curve)
-88dBv (lines, 5mV input, standard A-weighted curve)
-88dBv (lines, input at mini., standard A-weighted curve)
-104dBv (lines, volume at mini., standard A-weighted curve)
S/N ratio at loudspeakers : 97dB (flat with 6dB/oct. rolloff at 15Khz to provide noise bandwidth of 23Khz)
100dB (standard A-weighted curve)
THD : 0 (phono amp, rated level)
0 (phono amp, +20dB)
0 (line amp, rated level)
< 0,01% at 1Khz (line amp, +20dB)
0,02% (power amp, 1Khz, rated output)
0,01% (power amp, 1Khz, rated output, typical)
0,006% (power amp, 1Khz, 25W output)
Mains : 100 - 120 - 130 - 220 - 230 - 240V, 50/60Hz
Dimensions : 43 x 11,5 x 28cm
Weight : 9,5kg.
Radford HD250 : 0 topic
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page online since : october 2010
page updated : not yet
page type : LGT / KNB
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