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This is my first post on this phorum, but not my first restoration. I have done a dozen or more. I know just enough to be dangerous! I have decided to tackle a 41-290 that I have had sitting around for a few years. What a project! I have replaced all the electrolytics, the paper caps, and have a good start on the rubber coated wires.
There is a wax covered square block attached to the band switch, I assume it contains caps? Does this need replaced? & what would I replace it with?
Thanks!
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Hi Todd,
Welcome to the Phorum. I believe you are referring to the Bakelite block. If you go here:
http://www.philcoradio.com/tech/blocks.htm This will tell you what you need to know.
Eric
Lake in the Hills, IL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
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Todd, can you take a look at the chassis diagram and see what number the component in question is? I am looking at this in my 1941 RMS manual but do not see what item you are talking about.....
http://www.nostalgiaair.org/Resources/420/M0013420.htm
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I referred to part #65. I can't tell what #21 is.
Eric
Lake in the Hills, IL
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#21 is a dual mica condenser. They rarely fail, I would not replace it.
Note that it is part of the oscillator circuitry. Value is critical here, and note that both are 370 pF, an odd value to be sure.
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Thanks!
I fired the radio up for the first time last night. It is completely silent except for the crackle of dirty pots and the clunk heard when switching bands. I am assuming the audio amp section is fine, and the problem lies upstream of the band switch. I plan to clean those loctal tubes and sockets before I try to troubleshoot it further.
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Todd;
Item 65 is a dual .01 capacitor with the capacitors inside the bakelite enclosure. There are a number of threads on how to remove the internal parts that are potted in a black wax or tar-like substance. I restored a 40-201 which is similar and has the same part on the AC input circuit. These parts are particular safety related items and should be replaced with modern parts rated for AC input circuitry. The modern replacements are much safer for fire and smoke plus shock hazard issues. Since they are not visible unless the bakelite enclosure is removed and viewed from its bottom, most of us do not bother to repot these capacitors. It will make replacement in the future that much easier and no one will know unless they remove the part from the chassis again.
Definitely clean the tube pins and sockets. Usually the removal and reinsertion of the tubes in the sockets accomplishes some cleaning. However a thorough cleaning of the tube pins will certainly help. Deoxit and some mild abrasive materials can be used for cleaning the tube pins. Scotchbrite pads can be used in the cleaning process, but are not the only thing that can be used.
Check for reasonable voltage readings on the plate and screen grids of the RF and IF tubes. Check the Oscillator tube voltage readings. Record your readings and post them here and we can help you with further troubleshooting. You may want to also check resistance readings of the various RF transformers and coils. Be sure to make resistance readings with the set turned off and record those results and report them here too.
Joe
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Here's a link to a recent step by step tutorial on the Bakelite blocks
http://www.philcoradio.com/phorum/showth...p?tid=9107 and here's useful data on the blocks
http://www.philcoradio.com/tech/blocks.htm .
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Have you verified that all tubes are good?
If you have a way to inject audio and RF modulated audio, recommend:
1. inject audio signal on the high (non grounded) side of your volume control. If you get the signal strong in your speaker and can adjust volume with your volume control, the circuity is good from that point forward.
2. Inject audio signal modulated by 455KHz (IF) signal on grid of 1st IF tube. If you get signal to speaker, problem is before 1st IF. If no signal, inject same on grid of second IF tube. Same as above if you have or do not have signal.
This should help narrow down where the issue is.
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Thanks for the replies. I'm going to tackle the radio again this weekend. I'll clean the tubes and sockets first. I do have a tube tester, but it has been a little flakey lately. I'll test the tubes first, then dust off the signal generator.
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There is a thread on the Antique Radio Forums website covering a restoration of a 41-255 that was very helpful for my recent restoration of a 41-290. Here's the link.
http://antiqueradios.com/forums/viewtopi...69&start=0
Might help with your project.
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Wow! That's quite the thread. Thanks.
An update on mine: Both XXL tubes - the 1st det. and osc. are bad. So I am looking for replacements.
A RF signal placed at the antenna terminal comes through loud and clear, so I am hoping that fresh tubes will solve the issue.
I have removed the tuning cap for a thorough cleaning.
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Strange that both XXL are bad. Mine are original and the weaker one got put in the OSC. Might question your tube tester.
XXL is the same as 7A4
Mine 41-280 was also quit deaf. Someone had soldered the free end of the coupling stub to the padder (trimmer) on the left side of the tuning cap and that kills or sharply reduces the OSC.
Also note that Part 21 / 21A dual mica is only used when using the push buttons.
I ended up with a tiny artist brush and Deoxit on the band switch, upper / lower contacts on the push buttons and non-Loctak tube socket pins. One of the threads recommends one of those little dental brushes for the non-Loctal sockets.
Look on
http://www.philcoradio.com/tech/schema.htm for the link to
http://audiophool.com/Philco.html for Philco service bulletins and other resources
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"An update on mine: Both XXL tubes - the 1st det. and osc. are bad. So I am looking for replacements.
A RF signal placed at the antenna terminal comes through loud and clear, so I am hoping that fresh tubes will solve the issue."
If the you are passing an on frequency RF signal through (say 1000KHz) when tuned around that frequency on the dial and Broadcast band then the LXX tubes are not that bad.
Try putting in 455 and peaking the IFs Modulate it if you can and hook an AC voltmeter to the empty terminal board screw (external speaker) on the back of the chassis
If you have the tuning cap out for cleaning (or not) shoot the bearings and center ground spring wiper with Deoxit before you slap it back in.
(This post was last modified: 04-03-2014, 04:51 PM by
K7Sparky.)
