Philco 38-12 radio
 

Well just picked this radio up and seems to be common one and chanced turning it on using an inverter and it's got the typical buzzing that am radios have but it didn't pickup any stations but I'm going to recap it. I'll have to chance this after recapping because I have no clue if the tubes are good or not since these tubes are so early I gave away my tube tester that would have tested these now I have none to test them with. If anyone knows these radios , is there any known problems with these radios that need special attention.

Like most of the starter Philco sets, I think this one is relatively simplistic. Just don't forget about the bakelite capacitor block, If I recall correctly, this set uses one

I have two in my collection!
Standard transformer powered five tube radio.
Initial check procedure: Remove 84 rectifier tube and see if the rest of the tubes light up, of course with power applied. Replace the electrolytic caps and the coupling cap from the 75 plate to the 41 output tube. Make sure the two resistors are good in the bias line. Then try it!
Tubes are the last things I worry about in a radio that basic.

Schematic here:

https://www.google.com/search?q=phil...O2nPfkz-m59jM:

I don't see any capacitor blocks... looks pretty simple.

jr

What is that capacitor block which is listed as a compensator, whatever that is. :scratch2: how is anyone able to make out the colors for the values of the resistors in this radio, the colors are weird and don't make sense.

It looks like the power line filter is one of Philco's bakelite blocks.

Philco's name for trimmer condenser is compensator. Looks like the 2nd IF transformer is mounted on the back of the chassis with the compensator.
I don't remember the resistors used in the radio. Just use the schematic from Nostalgia Air.

Yeah, that's the one I was referring to, however, I've had experience with Philco substituting items sometimes. I've found capacitor blocks where they shouldn't have been, and tubular caps the same. Could have been factory, or someone replacing with OEM parts, either way they were genuine philco stuff. Either way, they matched the schematic, though not the under chassis diagram provided.

ARF has a pretty good page under their resto section that translates the part numbers into cap values for the blocks (sadly it does a poor job for the ones that contain resistors and caps)....I just chip the tar out with a couple different sized screwdrivers and hide the new caps inside the block....Since the blocks act as terminal strips it is cheaper, simpler, and better looking to restuff them rather than replace with new terminal strips.

While this radio is really simple the schematic is not so clear as to the values of the resistors since some number 3s look like 5s because of ink bleed on the paper so I guess the best way is to try to compair the value of the resistor with what it shows on paper with adding more for drift. :yes:

There is very little problem reading the resistor values on the N/A Schematic, plus every part is listed by number on the parts list.
Philco is the one that started using the odd-at-the-time values of resistors, ie 47K instead of 50K, 2.2 K instead of 2K or 2.5K etc.
They claimed that some color codes were hard distinguish under the then-new Mercury Vapor lighting, being used in their plant.

I have the NA schematic , even looking at it on line seemed Alittle bit of bleeding on the type. Well I don't have vapor lighting here, lol,lol :D

Well I took out the 84 and the other 4 tubes do light. So now I'm off to check resistors and recap.

Most of the riders manuals were poorly scanned back in the 90's and no one ever bothered to fix that. The original books are much better, but the print is rather fine...One day I gotta get me the full paper riders.

Someone at the WARCI meet had some paper issues. That might've been the one you missed. I have some duplicates from the shop that closed down.
Let me know what ones you need.
BTW, the N/A scans are pretty good.

Ok so it's all recapped now and it works but the volume has to be maxed to here anything the audio is super very low, but I am unable to test the tubes so I'm assuming the 84 is good as well as the 6a7 being its pulling in a station which is local here to me. So is it possible one of the other tubes may be bad like the IF, 78 or the 75 2nd Det 1st audio tube, or even the 41 output tube ? Maybe rule out anything else.

I don't know what the proper ohms should be on the Transformer on the speaker but I measured the primary input .730k ohms and the secondary to the speaker,2.0 ohms and the speaker coil itself, 4.5 ohms. I originally plugged it in and got the typical loud buzz and hum out of the speaker so if anything the speaker and coil should be good. The field coil that's on the speaker itself measures 1.758k

Did you check the voltages?
Those are all DC resistances on the output transformer, speaker and field coil and they look alright. Also the negative on the input electrolytic should go to the bias line instead the chassis. Also check the bias resistors, 400 and 75 ohm.

The 2 electrolytics, one is chassis ground the other is not . I just checked the schematic and the speaker output
primary does show its 450ohms I'm getting .730k. There is a 70 ohm resistor and it's ok but I don't see a 400 ohm resistor. the 190k I replaced with an array at 186k and the 490k I replaced with 470k .

Seems ok,

How long of an antenna wire are you using?

jr

Well the schematic shows 190,000 so that should be 190k . Wire for the ant is like 3feet long.

10'+ is better. 100'+ is ideal.

I'm pulling my hair out , this simple radio should work, well unless a tube is bad then I would have to get 4 of them since the voltages look good so then rectifier tube is good.:scratch2:

It doesn't look like you have many strong AM choices.

https://radio-locator.com/cgi-bin/lo...req=&sort=freq

Have you tried peaking the if transformers? Longer antenna wire?
Is the dial calibration fairly close, or does the set need alignment?

jr

I have one strong local am station and it comes in but no volume only max can I here it. I even tried the radio outside still no volume very low. The ant wire is really long. While listening to the station I tried tweaking the screws but it's all right on the money , I marked them befor touching them and it's right there. I went over my work and can't find anything. But if a tube is bad I have no way to tell which one it is since I don't have an older tester to test them nor do I have an idea which one it might be instead of buying them all. If I had an idea of what to try as far as testing to maybe see what tube it is that would be good.

You may be able to rule out audio by injecting audio past the detector and seeing if volume is adequate.

I was just about to ask what happened to standard troubleshooting? An inexpensive signal generator/tracer would make simple work of this, and one should be in every TV/radio hobbyist's possession.

.

What kind of reception do you get on another AM radio in the same location, especially the station you are receiving?
That Philco radio is just as hot as any other AA5 with similar circuitry. It's a standard AVC equipped radio, not one of those non-AVC circuits, where the volume control is located in the antenna and bias circuit.
Make sure the bias voltages are on the money as they affect the first and second audio stages. :scratch2:

If you don't have a signal generator, just touch the grid cap of the 75 tube... if a fairly loud hum/buzz is heard through the speaker, the audio section is likely working ok. Try the "one finger signal injection" both with the grid cap connector on and off the tube.

jr

Ok I have a cheap am radio and it works fine and loud strong signal, since the station is near me. The 75 tube cap off there is a buzz touching the cap and not all that loud and cap on less buzz touching it. The 6a7 wet my finger and touch the cap and the station comes in Alittle stronger. I will check the voltages on the 78 and 75 tubes again.

Ok the voltages, the 210 v is 211 v where there is 95 v I'm getting 97 v ?and the 2.5 v on tube 75 I'm getting 3.3 v and on the same tube the 2.3 v I'm getting 3.0 v .the 290 v on the rec tube I get 293 v. Minus 8 v I'm getting minus 14 v. The 90 v on 78 tube im getting 78 v . I would think the only one that's off a bit would be the output tube where the -8 v is -14 v and the voltage don't change with the volume being turned. I did check the volume pot which is .5 meg where it tests at .9 meg.

Did you check the 70 ohm and 250 ohm bias resistors? They set the -8 volts on the output tube.

jr

Yes I checked those, the 70 ohm is 69 ohms and the 250 is 265 ohms. If it's a weak signal causing the low volume I went and checked the ohms on all the coils except the can on top, they were good.

Now, I guess it's time to try some new tubes! Every thing else seems to be reasonably in order.

I guess that I am somewhat concerned about the high resistance of the volume control... perhaps disconnect the wire to the center leg and jumper it to the high end of the control and see if volume improves. :scratch2:

jr

No difference with the volume control. Is it possible that one of 2 Micas could be bad or shorted , 6 and 17 on the schematic. More so 17 right off the audio output tube.

Possible.... sure, not the most likely failure, but worth checking.

Even though the volume is low, is the sound undistorted?

jr

The sound is like any other am radio not clear like fm. Typical am and even the solid state radio I have has the buzz in the audio when on am. Those Micas are 81 years old and even in the tvs Micas were thought that they don't go bad but they do. I could clip it and check if any ohms are present which would not be good. Other then tubes the Micas are it there's nothing else, there's not much to this radio. Other then that the audio is good just like the solid state radio.

I've read posts about this 38-12 radio where a jack was put in to play other music so my question is, is it at all feasible to put a phone jack in this radio to plug into an I pod and listen to that music using the radio. If it's possible where would I be injecting the signal, which tube and what pins. And would one side of the input be chassis ground and the other to one of the tube pins. There is 1st IF and 2nd IF and audio amp, then goes to audio output. The first tube is the oscillator which I don't think that would be used for this purpose. :smoke:

Ok found the problem, the array of resistors to make up 190k bias resistor just didn't work but I found the right resistor and the volume is loud now. I also completed the iPod jack and that works great just flip the switch one way for iPod and the other way for am radio. Ok so it's upside down, it's this iPad.