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Marconi TF801D/1

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Front View [28K] Tuning Scale Tuning Control Attenuation Dial Waveband Selector Carrier Level Percent Modulation

  • Circa 1960
  • Covers 10MHz to 470MHz in five ranges, with
    the option of A.M. modulation.
  • 1% typical distortion
  • 11 Valves and only one transistor.
  • Original cost unknown, but must have been
    an absolute packet !
Interior View [13K]The main oscillator is based around a disc seal triode (DET22), which is housed in a sealed box (on the right in photo opposite). In order to stabilise the operating frequency, not only is the H.T. supply regulated but also the triode's heater current is regulated via a transductor. The operating current is switch selectable; higher output levels result in a reduction of the triode's operating life.

Also in the sheilded is a H.F. power output valve, the Mullard QQV02-6, driven directly by the DET22.

The unit includes a crystal calibrator circuit. A portion of the main output is fed into a 5MHz crystal oscillator. Presumably the calibration oscillator generates a lot of harmonics as these harmonics mix with the main signal producing a beat frequency, the audio component of which is amplified using the one and only transistor and fed to a set of headphones.

Waveband Switch [5K]The waveband selection switch is unusual in that you have to rotate the dial 1.2 times to switch to the next frequency range. No doubt this is a result of the clearences required between the switch settings.
SERVICE DATA Thanks to site visitors Ian Smith and 'Ziggy' for a copies of various parts of the service data. You can download a number of sections from the service data page.
CURRENT STATE Very clean inside and out. Apparently in working order too, but I'll give it a check out first though.
WHERE FOUND £15 at a computer fair amatuer radio rally held at the R.A.F. Cosford aero museum (well worth a visit if your into aircraft).

Interior View [22K] KT66 Valve Cluster of small valves 5Y3G Rectifier valve

Page copyright
J.Evans 2001-2003
Last updated
29th January 2003