Marconi TF801D Signal Generator

NOTES	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. 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).

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.

Marconi TF801D/1