I know this is very old thread, but I am looking for help before I give up. I found a working Philco 40-120 and I purchased a kit to add bluetooth to it. I was a tech nearly 40 years ago repairing calculators so I thought I could do this . I am clearly in over my head and can't even figure out how to pull the volume Potentiometer out, it appearst to have several wires stiffly soldered to it. What might be the best site for me to view the scehematic and possibly photos to help with this old guy figure it out?
Welcome to the Phorum, coffeeboy! I am splitting your post off to its own thread. The one you posted to has been dormant awhile, and you should get better results with your own. You say the radio is working, but has it been restored? If not, all paper and electrolytic caps must be replaced, as well as any out of tolerance resistors. Failure to do so only invites problems. 40's era radios had inferior rubber insulation issues such as cracking, splitting, and breaking away from the wire itself. Inspect all wiring in the chassis for these signs. If present you can either reinsulate the wire by sleeving with shrink wrap, or replace it entirely. If you do the latter, reroute the new wire exactly as the original.
You sure did pick a jam-packed chassis for this venture. Take your time and have fun. Lots of help available here to guide you along the way.
Here's the service info for your set, found in the Philco Radio Library located at the bottom of the page. Take care and BE HEALTHY! Gary
First off, Welcome to the Philco Phorum. Plenty of Phine Phriendly Pholks Phull of Philco Pfacts (see a pattern here?).
Secondly, don't worry about not figuring this out. It is a simple radio complicated by a couple of things, not the least being that this is a transformerless set.
Below is a section of the schematic that I marked up for installing an "Aux Input". This can be an RCA Jack, a 3.5mm jack or you can wire your Bluetooth receiver output here directly, but a jack is preferable:
Below is a closeup view to show the detail better:
The switch is the easy part. The red X (yes, poorly drawn. My art with a pen and paper is bad enough, trying to draw with the eraser type pointing device is worse!) indicates where you break the connection. There are 2 "ends" to the resistance element in a "pot" (potentiometer). The side that you are breaking into has a wire (possibly blue) going to the IF output transformer secondary (This is the detector output), one end of a 3.3MegOhm resistor (the input to AVC) and a 250 pF cap (Detector RF Bypass Cap). Once you break this connection, wire in a SPDT (single pole double throw) switch. The common of the switch goes to the volume control. the wires disconnected from the volume control go to one leg of the switch. The other leg goes to the pin terminal of an RCA Jack or the tip terminal of a 3.5mm phone jack.
Now for the dicey part. What to do with the other connection (the body of the RCA Jack or the phone jack).
A 120V outlet in the USA has one pin at "Neutral" potential, and the other prong at "Hot" potential. Neutral and ground are tied together at the Service Entrance equipment, making neutral potential and ground potential the same thing. This means that one prong of a plug is at ground potential when plugged in, and the other prong is 120V above ground. This set like almost all transformerless set is a "Warm Chassis" set. The difference between a warm chassis and a hot chassis is that the power line connects to the chassis of a hot chassis set bit in a warm chassis set, the power connects to the chassis through a cap, for the purpose of conducting RF but not the AC. Ordinarily, adding a polarized plug to ensure that the chassis remains at neutral potential, not hot potential will add a measure of safety. The problem here is that almost all of these AA5 or AA6 AC-DC sets put the power switch in the B-, filament return, chassis side of the radio. See the complete schematic from the link and the detailed area, shown below:
Because of this, if the plug is such that the power switch is at neutral potential and closed (on), the chassis at neutral potential, but when the switch is open (off), the low cold resistance of the tube heater string puts the chassis at hot potential. If the plug polarity is such that the switch is in the hot leg of power, the exact opposite occurs, with the switch off, the chassis is at neutral potential through the filament string, but becomes hot when the switch is on.
This becomes a large problem when adding an aux jack. If the return ("Body "of an RCA jack or "shield" if a phone jack) is connected to B- then the body of the MP3 Player, CD Player, etc. becomes hot. If connected to the chassis, it becomes "warm" and hum may occur. In the above diagram, I show the body of the RCA Jack going to "ground". This is the safer way to do this but the safest way of doing so is to make the following modification. Refer to the diagram below:
The blue line indicates the "B- and heater (filament) return" circuit. The first part of the mod is to disconnect all connections from the power switch and connect these wires directly to each other. The second step is to put the switch in the "Hot" side of power (the wire that goes to the pilot light and 53 Ohm resistor. The third step is to add a polarized plug with the wider pin going to the Neutral and the narrower ping going to hot. If the connections are made in this manner, then the return of the jack can be connected to B- instead of the chassis but care must still be taken, I would only do this if the jack is only to be used for the Bluetooth.
Finally, how to power the Bluetooth receiver. the easiest and safest way to do so is to use batteries, or if the radio has room, a power supply having a transformer. If using a high efficiency "brick", the output MUST be isolated from the power line.
Hope this all helps.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis
Thanks everyone. I went to electronics school back in the eighties. I worked for a few years repairing calculators, then left electronics for a great job offer not in electronics. I have forgotten more that I ever learned! I apreciate the help. I'm retired and thought it would be fun to pick up this hobby. The bluetooth module is this one:https://www.retroradioshop.com/collections/diy-bluetooth-kits/products/retro-vintage-or-antique-radio-bluetooth-upgrade-kit I purchased the radio off eBay. I was told the paper capacitors have been replaced. I see it has 2 new capacitors, that's all I see that looks new besides the power cord. I think I have it figured out, but I'm worried since Gary says "all paper and electrolytic caps must be replaced" and I only see the 2 new caps. I'll probably go ahead and see if I can get this module installed and see what kind of performance I get and go from there. Advice is always apreciated!
(This post was last modified: 01-23-2025, 02:22 PM by coffeeboy.)
A suggestion: when listing a link, try to make it not blend in the text as simple part of a line. It makes it more noticeable when you give it its separate line/paragraph.
Now, as for the radio you've purchased: since we haven't seen it, it would help if you showed some photos, especially of the underside of the chassis, the whole picture as well as the specific regions of it you care to discuss. This way we could at least guess as to what has been done to the radio.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Here are a couple photos of the Philco 40-120. I had the link to the bluetooth module correct, I wasn't sure so I re pasted it in and for some reason the link didn't work, sorry.
(This post was last modified: 01-23-2025, 05:05 PM by coffeeboy.)
From what I can see, the paper caps (I see five) have NOT been replaced.
One is the big 0.25uF tubular on the left, the other is market 30-4119 is on the right, then something that could be another one is under the first cap, right above it, and another one right above this one, between the two coils, and the 5th one is right below the big 0.25uF.
There should be 7 per the sch: 0.25uF (C8, with the wire wrapped about it), C4, C7 and C17 are 0.05uF; C22 and C26 is 0.01uF (after the volume pot) and C29 is 0.04uF.
It is possible that 0.01uF caps are disc ceramic and have been replaced. Not sure.
From the looks of them, they have not been touched/restuffed.
What has been changed is the electrolytic caps, you can see the two on the right, 22uF 200V.
I would change the paper caps.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Since I was a tech more than 30 years ago, with limited experience. I don't think this is a good first project. I was going to give it as a gift once I completed the bluetooth installation, but I think I took on too much for a first project. I'm rethinking now. Since the radio works well with AM, I may just use it for listening to news until I know what I am doing.
(This post was last modified: 01-23-2025, 06:16 PM by coffeeboy.)
With those old capacitors still in service it's not a question of if, but of when they will fail. They have a bad habit of taking out components with themselves. If you choose to operate it without restoration, know the chances you are taking. - Gary
"Don't pity the dead, pity the living, above all, those living without love."
Professor Albus Dumbledore
Gary - Westland Michigan
It is actually easy. Unlike some of us, who cut the old caps, gut them and restuff with new ones, all you have to do is to get these 6 caps (the values are in the sch or here, I listed them), cut them out (don't need to desolder), leaving some stubs, and solder the new caps to the stubs.
We have some people, who had never held soldering iron in their hands or knew Ohm from Amp before taking on a projects more complicated than that.
Basic safety applies, of course.
Considering the radio works, this is the matter of changing these 6 caps.
It would be desirable to measure resistors and change if needed, but this, unlike the caps, is not a safety question anymore. You could even do without alignment.
It is your call, of course, but sometimes the problem seems bigger than it is.
And you already took the chassis out. That's the hardest part.
And, as you could see, we are pretty responsive, especially to new members who have little experience and need some guidance.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
morzh
This is a great group. I really appreciate all the input. I am amazed people who have never soldered can do this. I was not even aware of paper capacitors, lol.
After graduating from Tech school in the eighties , I worked for a short period repairing calculators. I was offered a job in another field with good pay. I haven't done this work since then the eighties.
I was anxious for this, I purchased a new soldering station etc. think it might be a fun hobby, but I can barely read a schematic now or know a resistor value just by looking at it anymore . I will purchase another gift for my son I was going to give this too. I will think about what to do with this radio in the meantime. Thanks everyone!!!!
. I am clearly in over my head and can't even figure out how to pull the volume Potentiometer out, it appearst to have several wires stiffly soldered to it. What might be the best site for me to view the scehematic and possibly photos to help with this old guy figure it out?
. I will purchase another gift for my son I was going to give this too. I will think about what to do with this radio in the meantime. Thanks everyone!!!!
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