02-05-2010, 09:57 PM
Yes - 1000 ohms/volt was the standard for many years. 20K ohms/volt is much better, and the modern DMMs are in the 1 meg/volt or better range.
If your line voltage is 117, you're lucky - and your radios will like that. Most of us in the States have line voltages in the neighborhood of 125 volts. I once measured close to 130 when I was living in Evansville. Higher line voltages will also translate into higher voltages in your set.
284V on the RF tube plate is not surprising. When I was working on my Model 370 last year, I measured 280 volts on its RF, 1st detector and IF tube plates. Philco specs call for 250V on the plates of those tubes. As for the cathodes, I measured 3V on the RF, oscillator and IF cathodes; 7V on the 1st detector (mixer) tube. The front end of the 70 is the same as the early 90 front end. I was using chassis ground as common.
But 247V on the detector plate? That does sound quite high! Have you checked resistors (23) and (34)? Both 250K, 1/2 watt. And what about the 2nd detector cathode resistor (21)? 50K, 1/2 watt. If these check OK, then check your B-C resistor (38).
Try measuring again, using B- as your common point, and see what the difference is. You will probably read close to published specs on the cathodes by doing this.
If your line voltage is 117, you're lucky - and your radios will like that. Most of us in the States have line voltages in the neighborhood of 125 volts. I once measured close to 130 when I was living in Evansville. Higher line voltages will also translate into higher voltages in your set.
284V on the RF tube plate is not surprising. When I was working on my Model 370 last year, I measured 280 volts on its RF, 1st detector and IF tube plates. Philco specs call for 250V on the plates of those tubes. As for the cathodes, I measured 3V on the RF, oscillator and IF cathodes; 7V on the 1st detector (mixer) tube. The front end of the 70 is the same as the early 90 front end. I was using chassis ground as common.
But 247V on the detector plate? That does sound quite high! Have you checked resistors (23) and (34)? Both 250K, 1/2 watt. And what about the 2nd detector cathode resistor (21)? 50K, 1/2 watt. If these check OK, then check your B-C resistor (38).
Try measuring again, using B- as your common point, and see what the difference is. You will probably read close to published specs on the cathodes by doing this.
--
Ron Ramirez
Ferdinand IN
