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FERNSEH · 22nd Oct 2019, 1:05 pm

On Saturday I accompanied Gary (system A in this Forum) to Mikey's place in Solihull.
The objective of the 220 mile trip was to collect Gary's latest acquisition, a very rare 26" Philips G6.
Without delay we set about preparing the set for it's restoration. First, connect the set up to the variac and slowly introduce the set to mains power. Before long we were greeted with a thin white line across the screen.
In the G6 there is a 100ohm resistor inserted between the anode of the PL508 frame output valve and the primary of the transformer and it was getting very hot.
Well it seems that in the event of the frame oscillator failure the output stage draws excess current. The cause of the frame oscillator fault turned out to be the 1.5megohm anode load resistor of the ECC81. The G6 is unusual in having a cathode follower buffer stage between the oscillator and the grid of the output valve, the CF uses one half of a PCC85. The other triode section is used a frame flyback pulse shaper.
So that's the frame timebase working, although there is only just sufficient height. Replacing a 680Kohm 1watt resistor on the line timebase PCB resulted in having plenty reserve height adjustment.
It must be mentioned during the early stages of the restoration the PY500A boost diode took to glowing like a light bulb. This turned out to be a 0.33mfd decoupling capacitor in the heater chain.
Connecting the set to a source of signals gave us a picture of sorts. Not very good with what looked like maladjusted bandpass rejector coils and there is a lot of those in the IF amplifier.
We had fears that the IFs had been twiddled and it looked like a full realignment procedure would be required and that will not be easy because almost all the coil cores are stuck fast. No adjustment possible.
However, over time the picture did improve until the idea of realignment was abandoned. Thank goodness for that!
And the set even displays colour, but that condition known in G6 sets was noticed where the colour control operates in a strange manner.
More about the G6 restoration to follow.

DFWB.

22nd Oct 2019, 1:05 pm	#1
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	1971 Philips G6. On Saturday I accompanied Gary (system A in this Forum) to Mikey's place in Solihull. The objective of the 220 mile trip was to collect Gary's latest acquisition, a very rare 26" Philips G6. Without delay we set about preparing the set for it's restoration. First, connect the set up to the variac and slowly introduce the set to mains power. Before long we were greeted with a thin white line across the screen. In the G6 there is a 100ohm resistor inserted between the anode of the PL508 frame output valve and the primary of the transformer and it was getting very hot. Well it seems that in the event of the frame oscillator failure the output stage draws excess current. The cause of the frame oscillator fault turned out to be the 1.5megohm anode load resistor of the ECC81. The G6 is unusual in having a cathode follower buffer stage between the oscillator and the grid of the output valve, the CF uses one half of a PCC85. The other triode section is used a frame flyback pulse shaper. So that's the frame timebase working, although there is only just sufficient height. Replacing a 680Kohm 1watt resistor on the line timebase PCB resulted in having plenty reserve height adjustment. It must be mentioned during the early stages of the restoration the PY500A boost diode took to glowing like a light bulb. This turned out to be a 0.33mfd decoupling capacitor in the heater chain. Connecting the set to a source of signals gave us a picture of sorts. Not very good with what looked like maladjusted bandpass rejector coils and there is a lot of those in the IF amplifier. We had fears that the IFs had been twiddled and it looked like a full realignment procedure would be required and that will not be easy because almost all the coil cores are stuck fast. No adjustment possible. However, over time the picture did improve until the idea of realignment was abandoned. Thank goodness for that! And the set even displays colour, but that condition known in G6 sets was noticed where the colour control operates in a strange manner. More about the G6 restoration to follow. DFWB. Attached Thumbnails Last edited by FERNSEH; 22nd Oct 2019 at 1:19 pm.