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Philco 38-12 - Printable Version

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Philco 38-12 - radiola - 05-02-2011

My Philco 38-12 has a few problems as I attempt to repair it. First, the speaker is dead. I found a wire behind the speaker that doesn't look like it goes to anything considering it's length. I may have disconnected it when I covered the speaker with cardboard before working on it. It is coupled with a bare wire coming from the field coil on top of the speaker. Any help would be appreciated. Here are some pictures. The first was taken when I received it. Not a good pic since the flash failed. The other pics show the wire in question.
https://picasaweb.google.com/coatesaddress/May22011?authkey=Gv1sRgCJT97ezxl8qgswE&feat=directlink

Re: Philco 38-12 - Radioroslyn - 05-02-2011

Well it looks like the B+ lead from the audio is disconected. It should be a red wire. To double check measure the resistance from the red wire to the plate pin of the audio output tube. Should show a few hundred ohms or so. If it does the red wire would connect to the + side of your second filter cap. With this disconnected the will act dead NO AUDIO at all.
Terry

Re: Philco 38-12 - radiola - 05-02-2011

Hi. I did as instructed and no go--however I get no resistance when I put the black ohmmeter lead against the chassis. Whadda ya think?

Re: Philco 38-12 - Radioroslyn - 05-02-2011

Well I think you are doing it wrong. Go here http://www.nostalgiaair.org/Resources/236/M0013236.htm

Now go to the page that has the under the chassis voltage measurements. Look for the #41 tube socket. Find the pin that sez P 195v.
Connect ohm meter to that terminal and the red wire. MAKE SURE THE SET IS OFF AND UNPLUGGED! WHEN MAKING THIS MEASUREMENT.
Now what do you get?
Terry

Re: Philco 38-12 - radiola - 05-02-2011

Hi, Terry. I do have that schematic. I used that and this: https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=1yWc1K0cHBhnlfKD4hwov4zk_G42ZBcHVjfpa6leppZfWeq7kNvET5lmowCTZ&hl=en&authkey=CPrw16YC

The plate pin is pin 2, next to the heater. For some reason, the red wire (which had a black jacket on it, seems to be grounded, as shown on the ohmmeter. I can put one prong on the red wire and one on the chassis and get a closed reading. Thanks for the link. Also, when I touch the 41 tube, it's quite shocking if I touch a ground at the same time.

Re: Philco 38-12 - radiola - 05-03-2011

Update: I found the problem. It was below. I had replaced a pf cap on a bridge. The bridge had two posts combined together by the cap I replaced. I couldn't see that it was attached to both posts. The red wire in question (on the speaker) was coupled with the bare wire and then a jacket was slipped over it at the factory. The speaker is back and I'm back to the original problem. As always, I appreciate the help. Next:
The oscillator was dry rotted so I had to replace it. I used a P-C70-OSC for replacement. Now, however, I only get one station at the low end of the dial and one station leaks all the way up the dial. I've never changed an oscillator before. Perhaps someone can be of some help. Much appreciated!!

Re: Philco 38-12 - Radioroslyn - 05-03-2011

Glad you got your red wire issue figured out. As for the osc coil you will have to relie on the info that came with it to hook it up properly. If you can post a pic of the paper that came with it I'll see what I can do to get it working for you.
Terry

Re: Philco 38-12 - radiola - 05-03-2011

Thanks Terry. Here's the link. I used pins 1,3,4 & 5.
https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B_Rloe3jYEl3YmY1NDkxYjYtZDcxZi00Yzc4LWEzZmUtOWI5MGNhOTUxZGQ4&hl=en&authkey=CLWw25gP

Re: Philco 38-12 - Radioroslyn - 05-03-2011

Ok lets give this a whirl. On your new osc70 coil :
Pin 1 goes to #6 the 110pf cap
Pin 3 goes to chassis ground.
Pin 4 goes to grid 2 of the 6A7
pin 5 goes to B+ (High voltage)

Use the slug in the coil to set the low end of the band (550kc) and the trimmer on the tuning cap to set the high end (1600kc)

Terry

Re: Philco 38-12 - radiola - 05-03-2011

Terry, I'm going to give that a whirl tomorrow. Thanks for the info. I'll let you know. Your help appreciated!!!

Re: Philco 38-12 - Radioroslyn - 05-03-2011

Oh I meant to mention if it doesn't oscillate switch the connections on 4and 5
Terry

Re: Philco 38-12 - radiola - 05-06-2011

Terry, it worked. Your combination worked. Of course, it wasn't that easy. The new oscillator threw off the first I.F. Transformer and padders. It took me a couple hours to get the right combination of adjustments and slug positioning. That's with a signal generator. I'd get 600 in and 1300 would go out. Fighting both ends of the dial. I had to move the slug back to factory set before I could get all stations in. I still have fine tuning to do tomorrow. I appreciate your help. It worked and is much appreciated !!!!

Re: Philco 38-12 - Radioroslyn - 05-06-2011

Glad to hear it! Sometimes you can make the adjustment a bit easier by overshooting one end of the dial, like setting the high end at 1700kc and then when you set the low end at 550 the top end will fall in place,. sometimes
Terry

Re: Philco 38-12 - radiola - 05-06-2011

Well the little tuning job turned into a few hours with no luck. Since I installed the new oscillator, the IF cans and padders where all over the place. On top of that, it SOUNDS LIKE it's running in a variac at 50% and misaligned. The rich sound is gone and it sounds nasal. The stations are not lining up. I put my signal generator to the grid of the 6A7 tube, tried alignment there and it still sounds bad. Any ideas? Thanks!!!

Re: Philco 38-12 - Radioroslyn - 05-06-2011

Ok let's start at the beginning. Start by aligning the IF at 470KC. Hook your generator to the cap on the 6A7&chassis ground. Take an analog ac volt meter, hook it across the speaker terminals. Set it on the lowest ac range.Let the set and generator warm up for15 mins or so. With the generator set to 470kc and 400cy modulation listen for the signal with the volume up half way or more. Set the output level of the generator at the lowest level that you can get a reading on the ac volt meter.
Now you are all set up to align the IF transformers. Rap a small bit of tape around the tip of your screwdriver blade exposing only about a 1/16 of an inch of the blade. Some sets have B+ on the IF trimmers(plate side) so you don't want to short the B+out. Start with the IF can close to the 6A7. Adj both trimmers for highest reading on the ac meter. Go to 2nd IF can and do likewise. As you peak the trimmers adj signal level down to the minamon
reading on the meter.
Sometimes there is a bit of interaction between the two transformers so replete the adjustment. After you've done this your IF's are done. Don't go back and readjust the trimmers "best sound" or "it plays louder" or any other reason.
Dare I ask, has this set been serviced? New caps and such?
Terry