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PHILCO 38-15 Mod notes? - Printable Version

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PHILCO 38-15 Mod notes? - Bradley Rush - 11-29-2013

I have a new project 38-15
it has several caps (electrolites) 2 ea 16uf and a 8 uf. I will be looking to see where today. Just wondering if any one might have some modnotes that include these cap.

Look at where they are wired into schematically have added a pic of 38-15 in red is where the caps are the are electrolitic

The caps themselves look to be 1940-50 the work on the bottom of the chassis for that time looks right.

PICs

http://s1289.photobucket.com/user/TROG999/library/38-15%20Philco?sort=3&page=1

Thx in advance

Brad Rush

RE: PHILCO 38-15 Mod notes? - Radioroslyn - 11-30-2013

They look to be just wired in as replacements for the originals. I don't think Philco used SOLAR paper caps. This set have been serviced before back in the late '40's or so.
Terry

RE: PHILCO 38-15 Mod notes? - Joe Rossi - 11-30-2013

Hi Brad, Agreed, someone has been under the chassis back in the late 40's to mid-50's. However, this is a great looking radio!

RE: PHILCO 38-15 Mod notes? - Bradley Rush - 11-30-2013

Thx Joe
I bought it online

I have tried to be accurate as to the location of the caps.

I used the resistors they were attached to id.

RE: PHILCO 38-15 Mod notes? - Arran - 12-01-2013

If you can find the original service literature they will have an under chassis parts location diagram that will show you where the original paper caps were located. It looks like this set was serviced sometime in the late 1940s or early 1950s as the majority of caps are now of the Solar Sealtite brand. Oddly enough the Solar Sealtite caps are one of the few paper types that seems to hold up over the years, I've tested many of them on a resistance capacitive bridge and many will pass a leakage test. However I still do not trust them, it's still a good idea to replace with modern polyester film caps.
You are lucky in one way, whoever overhauled this set left the original Philco brand condenser cans in place and simply connected axial lead replacement electrolytics under the chassis. So you can either do the same with model replacements, or open up the cans and stuff new replacements inside for the authentic look.
Regards
Arran

RE: PHILCO 38-15 Mod notes? - Bradley Rush - 12-01-2013

http://s1289.photobucket.com/user/TROG999/media/38-15%20Philco/100_6620_zpsac485c9f.jpg.html

I do have the 38-15 schematic. What I have found is there are several resistors not in the schematics. Or I'm not able to read the resistor's.
If you look at where the two what I think are 1M ohm resistor's on the 75 tube socket. I can not find them on the schematic's.

Where the 1M tie together he has attached a pf cap that goes to #15coil.

I get the 250K red dog bone taking the place of the 190K is fine.

What I have found as well is I don't have a 78 tube but a 6D6. Because on both sides of the 6D6 someone increase the resistance. Looking at the 6D6 to see the difference between it and the 78.

Is this a Mod to use a 6D6 instead of a 78? Did Philco send out a recall notice? This does not look factory at all.

Still verifying the Caps Mr Rossi the first 16uf cap on the left of the bottom of my pic is a replace for the 12uf. But he went to ground with one side pics will follow because this is interesting too.

Above is a post of the bottom of my chasis with what I have identified. I have provided copies of the tube positions too.

RE: PHILCO 38-15 Mod notes? - vinzer - 12-01-2013

6d6 is a sub for a 78
will look at print to on check the resistors.

RE: PHILCO 38-15 Mod notes? - vinzer - 12-01-2013

I didn't see any 1 meg resistors like that on the print maybe some one else will know more than me.

RE: PHILCO 38-15 Mod notes? - Bradley Rush - 12-01-2013

so you agree they are one meg ohm resistors and the lil dog bone is a 250k?

Here are the mods as I see them:

http://s1289.photobucket.com/user/TROG999/media/38-15%20Philco/38-15_SCHEMATICMODS_zps24be876c.jpg.html?sort=3&o=0

All I can see in the addition of resistors because of the way he put the caps in this might of help keep the tube from over driving.

RE: PHILCO 38-15 Mod notes? - vinzer - 12-01-2013

yes but I would put it back to original I don't see those resistors on the print.

RE: PHILCO 38-15 Mod notes? - Bradley Rush - 12-01-2013

That was the plan but if this is a mod that will help it? Even after I return it to blue print?

RE: PHILCO 38-15 Mod notes? - vinzer - 12-01-2013

I have no idea if it will help or not I guess you could try it both ways to find out maybe somebody who know more than me will tell you.

RE: PHILCO 38-15 Mod notes? - Radioroslyn - 12-01-2013

I'd put the 78 back in it. Probably not much difference between the tubes in terms of making it a SUPER RADIO.
GL
Terry

RE: PHILCO 38-15 Mod notes? - Mondial - 12-01-2013

I agree with Terry regarding returning the 78 tube. The 6D6, while electrically similar to the 78, does not have an internal shield surrounding the plate and must be used with an external shield. Without one the 6D6 can cause regeneration and instability.

It looks like the two 1 Meg resistors and mica cap were used to provide delayed AVC to the IF and converter tubes by using one of the diodes of the 75 tube. This was standard practice on some Philcos and might be a factory mod. It looks like one 1 Meg connects to the cathode and the other to the AVC line. The common ends connect to the diode plate and the mica cap which feeds the IF signal from the coil. I would tend to leaving it as is, since the resistors and cap look factory original.

RE: PHILCO 38-15 Mod notes? - Arran - 12-02-2013

Try Here, this has an under chassis parts map:

http://www.nostalgiaair.org/Resources/239/M0013239.htm

Regards
Arran