Radford amplifiers
Below is a (incomplete) list of Radford designs in an attempt at chronological order. The prefix STA indicates a stereo amplifier. The prefix MA indicates a mono amplifier. The number indicates the nominal power rating.
Original Radford amplifiers:
Model
Information
STA12
(1960) Used EL34 output tube and EF86 with ECF82 driver tubes. The rectifier was a GZ34. Produced just over 12 Watts per channel and based on a Mullard 5/20 with good output transformers and some careful LF and HF phase compensation to keep the unit stable.
MA15
power Amplifier. Single channel version of the STA12 with slightly higher power output.
STA7
(1960) Very rare dual channel amplifier giving about 8 Watts from a pair of push-pull ECL86.
STA15 mk2
(1962) As above but output = 15 wpc
STA15 series 3
(1962) Uses EF86 input valve, ECF82 phase splitter/driver and 2 EL34s per channel. A single GZ34 provides rectification for both channels.
STA25 series 3
(1965) The first stereo version of the MA25 gave a conservative 25w per channel from EL34 output tubes and EF68 with ECF82 driver tubes. This amp is sometimes confused with the STA15. It can be identified by its manual bias adjustment and solid state rectifier both of which are not present on the STA15.
ISTA60
60wpc.
STA100
driver tubes were ECC88 and EF184. A solid state rectifier was used.
MA15
(1961) First monoblock, valve line up = EF86 ECC83 EL34X2 EZ81 rectifier
MA15 Series 3
(~1961) As above but uses EF86 ECF82 GZ34 Valve rectifier.
MA25
(1962) Valves used = EF86, ECF82, EL34X2, Diode bridge rectifier.
MA25 mk3
(1962) As above.
K25
A modified version of the MA25 for use with a BBC monitor loudspeaker manufactured by KEF. It featured a frequency shaping network, to flatten the response of the speaker, and a balanced input.
Radford pre-amplifiers/control units
DSM(~1961) Beautifully made control unit with 3 EF86 and 1 ECC83 per channel, a lot of electronics in a very small box.
SC2 A pre-amplifier with passive tone control system.
SC3 A three channel version of the SC2.The third derived channel was for a separate centre loudspeaker.
SC22 Feedback controlled tone controls, transistor disc stage and selective frequency RIAA equalisation network. There was also a switchable feedback rumble filter incorporated around the valve stage.
SC22p As SC22 with power supply.
Radford "Zero distortion" (distortion below circuit noise level) transistor amplifiers
ZD50 & ZD100 stereo power amplifier
ZD22 preamplifier
HD250 stereo integrated amplifier
Later Radford hybrid valve & transistor amplifiers
TT100 stereo power ampliier
Woodside Electronics amplifiers
STA25 renaissance
STA35 renaissance
STA50 renaissance (2004)
2009 Radford amplifiers
STA25 mk6
STA15 MK3 and SC22 preamp
A glowing example of a STA15 MK3
A Radford STA15 MK3 amplifier with its top cover removed
Radford loudspeakers
Radford also manufactured loudspeakers, tuners and other audio gear. An (incomplete) list of these is below:
Bookshelf
Tristar T90
Studio S90
Monitor M180
Studio S270
Studio S360
Monitor 90
Radford Tuners
FMT1
FMT2
FMT3
FMT4
FMT5 prototype produced, but never manufactured
Radford CD-Players
???
Radford Lab power supples (specifications approximate)
Model ?? 0-24V output switchable in 0.2V increments @ 2.0A and 240V @ 100mA
Model ?? Continuously variable 0-24V output with current limit variable up to 2.0A
Radford test gear
Arthur Radford was designing such high specification amplifiers for the time period that he was having problems measuring their performance due to limitations of the test gear. Radford set about designing new ultra-linear measurement and test tools to solve this problem.
Model
Information
DMS Series 3
LF Total Harmonic Distortion (THD) analyzer, to 0.003%, 10Hz-50k, 1mV-50v, portable.
LDO series 3
Low Distortion Oscillator. The instrument harmonic distortions are about 120 dB below the fundamental.
See also
Valve audio amplifier
Valve sound
External links
Radford Electronics Ltd
The Arthur Radford Appreciation Society
Yahoo Groups Radford Forum
Categories: Audio equipment manufacturers | Sound amplifier manufacturers | Loudspeaker manufacturersHidden categories: Orphaned articles from February 2009 | All orphaned articles | Articles needing cleanup from January 2007 | All pages needing cleanup
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