[don'tdomelikethat]

I've just finished replacing all the caps ( leaky Micamolds included) and resistors in a Philco 45, and no radio stations are coming in. I checked all the coils, and I "think" they are ok, all tubes check ok except for one of the 39/44 tubes which read a little low on a couple tube testers I have. I checked the voltages tonight against the Rider data, and get the following readings. What do you folks think? Bad coil somewhere?
6A7: P to K: 271 volts, should be 260
SG to K: G1: 3.23 v, should be 35
G2 : 293v, should be 135
G3 & 5: .220, should be 85
K to F: .228, should be 4.2
39/44 (1st IF): P to K: 270, should be 255
SG to K: 0, should be 75
K to F: .046, should be 3.8
39/44 (2nd IF): P to K: 268, should be 255
SG to K: .046, should be 75
K to F: .046, should be 3.8
The readings for the 80, 42, & 75 all check ok against the Rider's chart. I think the IF transformers are ok. The antenna coil, and oscillator coil, I'm not too confident about after noticing these readings, but both of those coils check ok for continuity, IF, and I say, IF I checked them correctly.I figure that's the problem, though. I hooked a sig. gen. to see if I could get a 460 kc., and 1400 kc. signal through, and nothing.I hooked the sig.gen. to both the antenna clip, and the grid cap of the 6A7. Any thoughts? Thanks!! Ed M.

[Ron Ramirez]

Hi Ed

I see you are getting B+ to G2 of the 6A7, so we're looking for a common symptom to loss of B+ to G3-G5 of the 6A7, and to the screen grids of the IF amplifier tubes (Type 39/44). This rules out the choke (59). Coils are probably O.K.

SO...my first thought is that either resistor (57) has gone infinite, or there could be a wiring error. (57) forms part of a voltage divider network that drops the B+ going to the screens of the 39/44 tubes and to G3-G5 of the 6A7. You said you replaced all of the capacitors, so that probably rules out a shorted screen bypass (22). It's unlikely, but resistor (56) could be shorted? Check out (57), make sure (22) and (56) aren't shorted, and let us know what you find.

EDIT: Noting your lower cathode to ground readings on the 6A7 and 39/44 tubes, I am assuming they are low due to the tubes not conducting because of their lack of screen grid voltage; but did you replace those flexible wirewound resistors ( 8 ) and (21)? If not, you should. Also check ALL of your resistors, and replace any that are more than 20% out of tolerance. Nevertheless, start your troubleshooting with the suggestions made in the paragraph above before you go any further.

[don'tdomelikethat]

Well, SUCCESS, yee-haw! Local AM talk radio is coming through ! I checked everything MrPhilco suggested, and one of the two new caps I used to rebuild bakelite block 22 was shorted to ground, as evidenced by both sides of resistor # 56 showing continuity to ground. I disconnected 56 and 57-both were good. That led me to check for a shorted #22. Sure enough, one of the two caps I used to rebuild the bakelite block was shorted to chassis ground. I pulled the block out of the chassis, the cap was still shorting out of the chassis. I looked inside, and one of the + wires from the original cap in the block was still in there touching the ground connection. I cut that wire out, reinstalled the block, and WA-LA, Dr. Joy Brown is coming through almost loud and clear before alignment. Moral to the story-ALWAYS make sure when rebuilding your philco bakelite blocks, that not only do you get the old caps out of the block, but ALSO any wire fragments from the old caps. THANK YOU RON!! I never would have looked where you directed me. There is so much talk about the Philco coils being bad, I pretty much figured that would be the problem.
P.S. Yes, I did replace flexible WW resistors 8 & 21-also, all the Micamold caps. They were Micamold brand, and I tested them on my Sprague TO-6, and all of them were leaky. It's now standard practice for me to at least check any mica caps for leakage.
THANKS AGAIN,
Ed Martin
WV

[Ron Ramirez]

Ed, you raise a good point. Most of us once believed that the old mica capacitors were safe to leave alone, but as all of these radios get older, more and more of the old mica caps are starting to show signs of failure. Checking these for signs of trouble should be added to our checklists as we go through the old radio chassis.

Glad to hear you found the trouble in your 45. Congratulations!