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FERNSEH · 18th Mar 2019, 2:34 am

Hi Nick,
the set under discussion is the phase 2 production version of the model 705T. Earlier sets were made for 405 lines only and employed a PY33 for the HT rectifier, that valve has a 29 volt heater which helps to reduce the value of the heater supply dropper resistor.
The convertible to dual standard operation phase 2 sets use a BY100 silicon diode for the HT supply. The 625 converter unit requires 51 volts for it's series heater chain and when the unit is not fitted that voltage has to be dissipated as heat in the heater chain resistor R159, 15.5watts!
The 600 and 700 models have two printed circuit boards, the lower one as seen in the attachments is the timbase and the upper one is the signals board. It's a similar arrangement in the 1962/63 fully dual standard models using the 800 and 850 chassis.
The 405 only 600 series models are much nicer than the 625 convertible sets.

DFWB.

18th Mar 2019, 2:34 am	#3
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ferguson 705T Senator. Hi Nick, the set under discussion is the phase 2 production version of the model 705T. Earlier sets were made for 405 lines only and employed a PY33 for the HT rectifier, that valve has a 29 volt heater which helps to reduce the value of the heater supply dropper resistor. The convertible to dual standard operation phase 2 sets use a BY100 silicon diode for the HT supply. The 625 converter unit requires 51 volts for it's series heater chain and when the unit is not fitted that voltage has to be dissipated as heat in the heater chain resistor R159, 15.5watts! The 600 and 700 models have two printed circuit boards, the lower one as seen in the attachments is the timbase and the upper one is the signals board. It's a similar arrangement in the 1962/63 fully dual standard models using the 800 and 850 chassis. The 405 only 600 series models are much nicer than the 625 convertible sets. DFWB.