The PHILCO Phorum

Greetings to all in Philco land!! I am brand new to this site, but have been rebuilding old radios since i was a teenager. Its a labor of love! I have run into one of "those" that is the oppositte of keep it simple stupid. I have an 81, that will not play for anything! I have completely recapped the unit, using chuck's method of rebuilding the blocks. I replaced all the dog bones, and filter caps. The tubes are very strong, and I have checked all my transformers and all windings are within 3% of dc resistance specs. Soo y does it not pick up stations??? I know my AF amp is fine, having injected a signal into the top cap of my detector/af amp. I checked, I have an oscillator running, and doin the math, it is right on the money frequency wise. I have noticed that the amplitude of my oscillator diminishes as I get towards the high end of the bc band. I have put my signal generator on it, and i have my if signal going into my if transformer (18). It is of adequate p-p amplitude. Coming out and going to my detector, I have almost nothing. With generator maxed out, i can get a barely disernable amt of audio out of the speaker. I replaced my 4 meg resistor (19) as well. What obvious in front of my face problem have i overlooked?? Has anyone else run into this problem? I would greatly appreciate any help on this one.
Rick Icon_smile

OK.. made a few more checks and wo is me.. i had an open antenna coil primary. I took the coil apart and discovered someone else has been here before me. I rewrapped the primary after fixing two breaks, and now i can get it to tune stations, but volume is very very low. Again, I put a signal directly into the 2nd det grid and i have gang buster volume from an external audio source. I have tried alignment and it does not help. One note I will mention, is that when i inject my 460khz modulated rf signal into the grid of my det/osc my volume is extremely low. It acts like it has a dead IF ckt. I followed the suggestions on the web page and changed the 4 meg res (19) to the recommended 2 meg and it does not help. Where am i going wrong. I have subbed out my new 78's with the old ones, and other ones,, and still audio is low. I removed the IF transformer (18) physically inspected the windings, and checked the dc resistance.. all good. Again,, thank you in advance.. and any help is appreciated.

Rick

Also look thru the various SERVICE TIPS for the Models 80, 81 and 84 on my site (URL below).

You mentioned changing out 78s? The 81 uses Type 77 tubes, not Type 78. This could be a key to some of your problems? Check it out.

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Chuck Schwark

Ron Ramirez