UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Aga Baltic AH37. Need help identifying old capacitor from 1930s radio

Mike. Watterson · 18th Oct 2018, 10:21 am

That works. Though don't confuse field coil with humbucking coil, if there is one. It's lower resistance. The polarity of that coil increases or decreases hum from field coil.
I've not looked at schematic.
Just make sure there are no leaking capacitors, usually every paper dielectric type. I usually check HT electrolytics for leakage by connecting 32V DC PSU in current limit mode to a set with it unplugged. That also reforms them. Excessive leakage pulls down HT. Lack of capacitance (dried out) creates hum, or on a cathode resistor reduces gain (loudness). A leaky AGC capacitor increases gain. If there are screen grids (Tetrodes and Pentodes etc, the g2), then a leaky capacitor to ground will dramatically reduce gain (little volume).
An open circuit IFT coil, or dry joint where wire of coil is on tag may still work due to capacitive coupling, but volume will be low.
Also check volume control from wiper and all the valve sockets.

18th Oct 2018, 10:21 am	#128
Mike. Watterson Heptode Join Date: Dec 2014 Location: Limerick, Ireland. Posts: 901	Re: Aga Baltic AH37. Need help identifying old capacitor from 1930s radio That works. Though don't confuse field coil with humbucking coil, if there is one. It's lower resistance. The polarity of that coil increases or decreases hum from field coil. I've not looked at schematic. Just make sure there are no leaking capacitors, usually every paper dielectric type. I usually check HT electrolytics for leakage by connecting 32V DC PSU in current limit mode to a set with it unplugged. That also reforms them. Excessive leakage pulls down HT. Lack of capacitance (dried out) creates hum, or on a cathode resistor reduces gain (loudness). A leaky AGC capacitor increases gain. If there are screen grids (Tetrodes and Pentodes etc, the g2), then a leaky capacitor to ground will dramatically reduce gain (little volume). An open circuit IFT coil, or dry joint where wire of coil is on tag may still work due to capacitive coupling, but volume will be low. Also check volume control from wiper and all the valve sockets.