Vertical height changes with beat of bass tones in the audio

[LukeSimon]

I have a late 1960s Panasonic AN-72 that I replaced all electrolytic, paper, and oil capacitors in. Before replacing the caps, there was extreme distortions in the raster such as a rolling horizontal warping of the horizontal deflection with what looked like a 60hz hum bar. After replacing the caps, everything is great except for a very subtle decrease and subsequent increase in the vertical height whenever there is a bass beat like a bass drum beat. Higher pitched beats do not cause the vertical height to change.

Which parts of the circuit can cause this? Can it be in the IF stages, or is this just a decoupling capacitor and resistor in the audio section that are out of spec?

[zeno]

Interesting problem.
Since the bass notes will draw the most current I would suspect either
a bad filter cap or the power supply isnt regulating ( if a solid state set).
If its a tube set a few were known for bad vert out transformers. They
gave very distorted vert & there would be wax all over the place.
I will pull up the manual tomorrow if I got it.

73 Zeno
LFOD !

[LukeSimon]

Here is the manual. It is not a solid state TV, and it uses mostly tubes.

It does have a single transistor in the UHF tuner, and the B+ power supply and high voltage anode power supplies both use semiconductor rectifier diodes, but they are not using any voltage regulation. The boosted B+ power supply (Bb) uses the tube damper diode for rectification, and the audio amplifier uses the boosted B+ power.

The vertical height fluctuation is about half to one full scanline in height. So it is minor. Like I said, I replaced all electrolytic caps. I measured the old and new caps for capacitance, ESR, and current leakage (at circuit voltage). The old electrolytic filter cap, a multi-section cap, was out of spec. The new old stock multi section electrolytic that I replaced it with is well within spec after reforming it using a bench power supply.

The audio amplifier circuit appears to use C212, a 3uF electrolytic capacitor as a decoupling capacitor that is attached to the boosted B+ power (Bb). I replaced it with a 3.3uF polypropylene film capacitor, so I doubt it is the culprit, unless Panasonic skimped on the capacitance, and even when new this TV had a bit of raster size fluctuation with bass beats.

Maybe I just need to upgrade C212 to an even higher capacitance? I have worked on many 1990s CRT TVs as a hobby. This is my first non-solid state TV. So the boosted B+ power supply is a new concept to me. I read RCA’s Bernard Grob’s textbook “Basic Television”, which explains how boosted B+ increases the B+ voltage by using the residual current from the horizontal deflection damper diode.

[old_tv_nut]

Is it visible at a distance of 10 feet? If not, it is probably within factory specs.

[LukeSimon]

Originally Posted by old_tv_nut

Is it visible at a distance of 10 feet? If not, it is probably within factory specs.

Not visible at 10 feet.

[Electronic M]

Originally Posted by LukeSimon

Here is the manual. It is not a solid state TV, and it uses mostly tubes.

It does have a single transistor in the UHF tuner, and the B+ power supply and high voltage anode power supplies both use semiconductor rectifier diodes, but they are not using any voltage regulation. The boosted B+ power supply (Bb) uses the tube damper diode for rectification, and the audio amplifier uses the boosted B+ power.

The vertical height fluctuation is about half to one full scanline in height. So it is minor. Like I said, I replaced all electrolytic caps. I measured the old and new caps for capacitance, ESR, and current leakage (at circuit voltage). The old electrolytic filter cap, a multi-section cap, was out of spec. The new old stock multi section electrolytic that I replaced it with is well within spec after reforming it using a bench power supply.

The audio amplifier circuit appears to use C212, a 3uF electrolytic capacitor as a decoupling capacitor that is attached to the boosted B+ power (Bb). I replaced it with a 3.3uF polypropylene film capacitor, so I doubt it is the culprit, unless Panasonic skimped on the capacitance, and even when new this TV had a bit of raster size fluctuation with bass beats.

Maybe I just need to upgrade C212 to an even higher capacitance? I have worked on many 1990s CRT TVs as a hobby. This is my first non-solid state TV. So the boosted B+ power supply is a new concept to me. I read RCA’s Bernard Grob’s textbook “Basic Television”, which explains how boosted B+ increases the B+ voltage by using the residual current from the horizontal deflection damper diode.

Thanks for posting the manual I have an AN-82 it covers. I fixed insufficient vertical deflection on mine without the manual but it's nice to have one if I ever need it.

[zeno]

The boost is the common factor. It usually feeds the vert height
& the audio.
Look for the boost filter cap. Usually its between boost
& B+. Look around the bottom right. Unfortunately the schematic is to small
find it.

73 Zeno

[zeno]

C212 is the boost filter. 3mfd, a likely suspect.
C413 also is
R 414 may be going high ohms

Boost also feeds the vert, comes in on the V. lin control
Boost feeds the plate of the audio det 4DT6. This is dont to disable
the audio if HV goes away.