Happy new year to all the fellow Vintage TV weirdos!
I've got a fellow collector and his 10yo daughter holidaying at my place at the moment. It was too hot and humid to venture outside so I though I'd put another old TV on the bench.
The one we chose was a base model Philips 11k series from the mid 60s. Some nostalgia for me because the company I worked for in the late 60s had these sets in their rental fleet. One of my first jobs there was to check out returns and get them ready to go out again.
So we ran it up on the dim bulb. It looked like it was going to be a runner despite looking like being a very high hours set. But then the line scan started to collapse.
Now Philips in Oz continued to use some wax paper caps in the higher voltage positions well after everyone else had given up on them. I never understood why because, although Philips themselves at the time didn't make "mustards" in voltages over 400, there were 3 local manufacturers who did make high voltage polyesters.
Anyway, sure enough, the .056uF 1000V boost cap had failed. So while we were at it we replaced the remaining five Ducon waxies.
Also while we were at it we decided to re-instate the DC restoration diode that was omitted in production for this base model, replaced with a wire link. Why? Who can understand the mind of the Dutchman?
All now looked good except for some occasional black splashes of noise - this was fixed by replacing the 6Y9 (EFL200). Here is the TV in service position, wish all TVs were this easy to get at!
And then the contrast started increasing, eventually resulting in a lockout overload condition. AGC line measured +4 volts. Looking at the circuit the only possible culprit was C308, 220pF, one of those Philips white tubular ceramics. I've circled it on the schematic. When removed it measured 1.5 megohms on the meter.
But what does this cap actually do? Can anyone tell me? I've been unable to find any difference in AGC performance with or without the cap fitted.
Something I remembered from 50+ years ago was the set's tendency to lockout when switching from an unused channel to a strong signal, which is what this set was doing. This thing has a stupidly high IF gain, AGC only on the 1st stage and (not shown on the attached version of the circuit) a 3.3M resistor to ground at TP4 shunting the IF AGC, a part we used to snip out back then. Snipping it fixed the lockout here as well.
The original high hours Philips CRT is bright but defocusses on highlights regardless of the setting of the focus pot. The white crushing is a camera artifact. Not bad apart from that.
@irob2345 I thought it was the gating pulse for the AGC, the circuit shows a 120v line pulse at that point.
That is first thoughts but will probably be far from correct.
The IF transformers are typically Philips.
Frank
That's what I thought at first but although G2 of the 6CM5 / EL36 has some ripple on it, it slews too slowly to have much effect through a 220 pf cap.
Maybe it was intended as an anti-lockout measure so that AGC could still be developed with the line osc unlocked but if so it's not effective.
I don't know the "correct" answer.
Nice looking set. The layout looks very similar to Philips F2ZN chassis we had here in New Zealand at the time. The F2 was a live chassis with series string heaters and two big dropping resistors at the top of the circuit board, at least your chassis is isolated. 😀
I've have had those white tubular ceramics fail in the past, one was on a Hi-Z Philips mantel set that was breaking down and causing a DC voltage to 'leak' into the tone control section which upset a few things!
My You Tube Channel for those suffering from insomina - Youtube Glenz1975
