Friday, June 10, 2011

Radford Electronics

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

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