02-08-2020, 08:17 AM
(This post was last modified: 02-08-2020, 08:20 AM by Mike Watterson.)
Here is under the removed chassis as received.
Loose Mains wire is off adjacent tag to soldered one. It goes via wavechange switch and volume control switch to chassis. The other wire goes to the rectifier, direct. The large grey RS cap is thus across the mains when the set is on and on mains.
It's no doubt a replacement of a waxie. We should really call them paper dielectric capacitors as not all are card tubes coated with paraffin wax. The right proportions of Petroleum Jelly and candle wax (both paraffins) would likely be identical. The paper is impregnated with a lighter paraffin oil except in the most expensive military capacitors that use a different oil. Plastic and metal packaging was used. Some PIO only use paraffin and rely on hermetic seals. Plastic film are better.
The medium grey resistor is the 1800 Ohms filament chain ballast. One side is either the battery voltage or mains derived 85V and the other side connects via the wavechange switch to the filament chain on mains settings.
I'm thinking I should measure current and voltage on the ballast and dropper resistors as they likely higher resistance when hot. Depends on what sort of wire is used. You can see seven original paper caps and the dubious RS part. The ninth paper cap is on top of the chassis in series with LW contacts for battery and mains to the LO section of the tuning capacitor.
The bright yellow sleeved 100uF Plessey capacitor was bad. I often find the two part plastic low voltage caps are dried out. The low voltage cap I've most often replaced is on the FM detector, which are not all discriminators, but almost always are + to chassis.
Loose Mains wire is off adjacent tag to soldered one. It goes via wavechange switch and volume control switch to chassis. The other wire goes to the rectifier, direct. The large grey RS cap is thus across the mains when the set is on and on mains.
It's no doubt a replacement of a waxie. We should really call them paper dielectric capacitors as not all are card tubes coated with paraffin wax. The right proportions of Petroleum Jelly and candle wax (both paraffins) would likely be identical. The paper is impregnated with a lighter paraffin oil except in the most expensive military capacitors that use a different oil. Plastic and metal packaging was used. Some PIO only use paraffin and rely on hermetic seals. Plastic film are better.
The medium grey resistor is the 1800 Ohms filament chain ballast. One side is either the battery voltage or mains derived 85V and the other side connects via the wavechange switch to the filament chain on mains settings.
I'm thinking I should measure current and voltage on the ballast and dropper resistors as they likely higher resistance when hot. Depends on what sort of wire is used. You can see seven original paper caps and the dubious RS part. The ninth paper cap is on top of the chassis in series with LW contacts for battery and mains to the LO section of the tuning capacitor.
The bright yellow sleeved 100uF Plessey capacitor was bad. I often find the two part plastic low voltage caps are dried out. The low voltage cap I've most often replaced is on the FM detector, which are not all discriminators, but almost always are + to chassis.
