Philco 84B Power Transformer - Printable Version
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RE: Philco 84B Power Transformer - gregb - 04-19-2014
Just so I have a better understanding, do you have any electronics background at all? This will help me to provide better answers and suggestions for you.
Gregb
RE: Philco 84B Power Transformer - bdi1976 - 04-19-2014
OK guys... my 3 year old ran over and grab the antenna wire and bingo - the news started playing. Pretty clear, but a very narrow bandwidth. Took long to tune it in perfectly. But, although it would be a good job for him to stand there all day holding the antenna wire for me, he's not going for it. What does this indicate is my issue? Also, strangely enough, I'm in Philadelphia where there are at least 10 AM stations, but only this one came in. Thanks for any next steps-
bdi
RE: Philco 84B Power Transformer - bdi1976 - 04-19-2014
Hey Greg- To answer your question, I have been spending about 2 hours per day researching electrical theory, tubes, and restoration for the past 4 or so months, so I am completely self-taught at this point. I have a decent understanding of the set, but sometimes locating a circuit in there confuses me. I seem to be getting close if you saw my last post. Thanks for all of your input and any suggestions on my reception problem-
bd
RE: Philco 84B Power Transformer - bdi1976 - 04-19-2014
I just doubled the length of the antenna from 10-20 feet. Now the channel comes in completely loud and clear, without my son as a second antenna. But all other local channels don't come in. The one that comes in is at the very end of the dial.
RE: Philco 84B Power Transformer - gregb - 04-19-2014
Did you find the source of the low voltages on the 77 tube, getting those up to spec will improve the reception a fair bit. Are you setup to do an alignment? If so that may help as well.
Gregb
RE: Philco 84B Power Transformer - morzh - 04-19-2014
Bdi
Not sure how much you really appreciate the nature of what you are dealing with fixing tube radios, but both my 9 year old and 3 year old stop at the very threshold of the room where I do it and do not proceed without my telling them so. And if they ever forget they get yelled at. Loudly. Let alone trying to grab any connected or unconnected wire.
I suggest you institute the same policy lest you be biting your elbows one day.
RE: Philco 84B Power Transformer - Steve Davis - 04-19-2014
BDI, I'm assuming we are talking about the 2nd detector 77. The voltages you posted are right in the ballpark. The plate should be 70 volts and the screen grid should be 23 volts.
You are receiving only one station near the low end of the band. That makes me think the oscillator is not working. If you have a working radio, tune it to about 1460 and place it next to your 84. Now, tune the 84 to 1000 and rock the dial a little. You should hear a squeal come and go in the working radio. If you don't hear a squeal, we need to look at the oscillator section.
Steve
RE: Philco 84B Power Transformer - gregb - 04-19-2014
Well after looking at the voltage chart I see what Steve is talking about. I had not looked at the chart and assumed BDI was checking the correct tube, never assume!
BDI, try Steve's suggestion and let us know what happens.
Gregb
RE: Philco 84B Power Transformer - bdi1976 - 04-19-2014
Sorry - I was checking the tube sheets by the mfr; not the philco specs. All tubes voltages are correct but the output/42 is a little high (255V- should be 225). Also, the detector/77 is a little high for the screen grid (117V/ should be 95). I played it for 2+ hours today, playing the one channel which was very clear and loud. I could also hear 4 other faint stations. Then suddenly it just started buzzing across all bands now...no channels at all. I checked all voltages again...all OK. I tried another radio nearby, but heard no squeal, so I guess osc is malfunctioning? Seems strange that it worked for over 2 hours though. Any input is appreciated. Also, Morzh, I appreciate your safety tips. It was in a safe area, but the antenna was laying across the room. I'll definitely take more care in the future. Thanks-
bdi
RE: Philco 84B Power Transformer - Steve Davis - 04-19-2014
Most likely, the oscillator has not been working all along. Sometimes a radio will pick up a strong station even when the oscillator isn't working. Try trading places with the two 77 tubes and do the oscillator test again.
Steve
RE: Philco 84B Power Transformer - bdi1976 - 04-19-2014
Hey Steve- I swapped 77s but no change... only buzzing. I rechecked the osc coil continuity=3.8 Ohms and antenna coil continuity=7 Ohms. No squeal out of the second AM radio. Should I remove the osc coil and visually check it out? THe continuities gave me hope that both coils were good. What do you think ?? Thanks
RE: Philco 84B Power Transformer - bdi1976 - 04-19-2014
one other thing I noticed - the rectifier P-P was 695V (supposed to be 630V) - about 10% high. Not sure how significant this is.
RE: Philco 84B Power Transformer - vinzer - 04-19-2014
that should not be a problem that is caused by todays higher line voltage.
RE: Philco 84B Power Transformer - Steve Davis - 04-19-2014
The next thing to do is check the voltages on the 77 detector/oscillator.
Steve
RE: Philco 84B Power Transformer - bdi1976 - 04-19-2014
Steve-
All voltages are good as previously posted. I checked all of them for all tubes. All are good or a little higher than specifications
BDI