08-20-2013, 03:26 PM
First, I want to thank those who have responded to my question about the unknown cap. Now I want to delve further into my inquiry about the bad output trans. and , hopefully solicit some responses on this.
I have been pondering this problem for several days and have come up with the following questions and observations:
1. The philco sch. says the plate current on each 45 tube is 30ma at no signal. From this value, I conclude that the radio is "fixed bias" and the max. signal plate current is approx. 138ma. This thinking comes from the 45 tube info. Is this correct?
2. Looking at the Hammond 125 series of output tr.'s, it looks like an impedance match could be made using the .7ohm speaker imp. to the input imp. necessary to drive the speaker. The tube info says 3200ohms(fixed bias, 5200ohms self bias) but the philco tech section info. on this site says 6700ohms output trans. imp. Which is correct? I realize that at max. volume that the plate current would overload the Hammond 125 series but wonder if volume levels are kept at normal listening levels if this would work? According to chart, the Philco output tr. has a pri. res. of 500ohms. I have measured a Hammond 125c at 275 ohms. Would this raise the plate voltage to an unacceptable level?
3. Surely some one has faced the bad output tr. problem before. What solutions are there?
Scott
I have been pondering this problem for several days and have come up with the following questions and observations:
1. The philco sch. says the plate current on each 45 tube is 30ma at no signal. From this value, I conclude that the radio is "fixed bias" and the max. signal plate current is approx. 138ma. This thinking comes from the 45 tube info. Is this correct?
2. Looking at the Hammond 125 series of output tr.'s, it looks like an impedance match could be made using the .7ohm speaker imp. to the input imp. necessary to drive the speaker. The tube info says 3200ohms(fixed bias, 5200ohms self bias) but the philco tech section info. on this site says 6700ohms output trans. imp. Which is correct? I realize that at max. volume that the plate current would overload the Hammond 125 series but wonder if volume levels are kept at normal listening levels if this would work? According to chart, the Philco output tr. has a pri. res. of 500ohms. I have measured a Hammond 125c at 275 ohms. Would this raise the plate voltage to an unacceptable level?
3. Surely some one has faced the bad output tr. problem before. What solutions are there?
Scott
