02-09-2007, 03:02 PM
Problem with Philco 20: Please take the schematic at http://www.philcoradio.com/tech/images/20a.jpg as reference
I replaced inside of filter cap can with 20microF electrolytes (1-2, 1-3, 1-4). I get 307V at point D (it should be 250V), I get 346V at entrance to choke (pin 2 of filter can), I get -8V at point B, and 55V at points C. The 55V at the C's seems ok (current of the 71A's (2x18mA) on [1400 + 187 = pins 1-2 + 2-3 of the multiresistor 25]Ohm). So, B should be at 187/(1400 + 187) = 12% of 55V = 6.5V. The schematics at nostalgiaair.org, however, says the grids of the 71A's (meaning point B) should be at 50V !!! How can that be?
Questions: 1. what should I get at B and C? 2. why do I get way too much voltage at D? 3. could it be the too high values of the filter caps?
I replaced inside of filter cap can with 20microF electrolytes (1-2, 1-3, 1-4). I get 307V at point D (it should be 250V), I get 346V at entrance to choke (pin 2 of filter can), I get -8V at point B, and 55V at points C. The 55V at the C's seems ok (current of the 71A's (2x18mA) on [1400 + 187 = pins 1-2 + 2-3 of the multiresistor 25]Ohm). So, B should be at 187/(1400 + 187) = 12% of 55V = 6.5V. The schematics at nostalgiaair.org, however, says the grids of the 71A's (meaning point B) should be at 50V !!! How can that be?
Questions: 1. what should I get at B and C? 2. why do I get way too much voltage at D? 3. could it be the too high values of the filter caps?
