Philco 38-7 - Printable Version
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RE: Philco 38-7 - Ron Ramirez - 08-14-2018
When (29) is closed, the audio is shorted to ground.
Try disconnecting one end of the wire going to (29) and try again.
RE: Philco 38-7 - Radioroslyn - 08-14-2018
+1
Or if it's easier you can measure the resistance from the vol cntrl wiper to chassis gnd if measures shorted or a very low resistance there's your problem.
RE: Philco 38-7 - cpollock - 08-14-2018
When I restored my 38-7, the wire was disconnected between the switch (part 29) and the volume control, and it works fine. In the spirit of restoration I hooked it up, but the noise it created when turning the dial was not pleasant, so I just left it disconnected. The switch is just a slider mounted on the tuning dial that shorts to a piece of copper, and there is enough roughness on the slier to create a lot of noise. So in my experience there is no harm in removing it. However, you should be able to open the switch by actuating the knob on the tuner, so it should be relatively easy to test without getting out the wire cutters.
Is your volume control okay? I ended up replacing mine with a ganged pair of 1M audio taper pots.
Also, this seems of no consequence, but your schematic is slightly different than mine in appearance. My speaker symbol is aligned with the top of the output transformer, while yours is below it. Everything else looks identical. I wonder why Philco would have two schematics? Mine came from AntiqueRadioSchematics.
Above you mentioned there was no HV voltage on 6J5G. Did that get resolved? Seems like that is the obvious problem.
Good luck! My grandkids were listening to mine all weekend on the local oldies station.
Clif
RE: Philco 38-7 - Radioroslyn - 08-14-2018
Hi Clif,
The 6J5 isn't going to have any HV applied to it as it's being used a a detector/avc diode. The only voltage found there is going to be a small amount of ac (the rf signal from the IF stage).
RE: Philco 38-7 - PhilcoPhan1936 - 08-14-2018
(08-14-2018, 06:25 AM)Ron Ramirez Wrote: When (29) is closed, the audio is shorted to ground.
Try disconnecting one end of the wire going to (29) and try again.
Still deaf as a post.
Printing up a fresh schematic and going over every connection and part with a fine tooth comb.....
RE: Philco 38-7 - PhilcoPhan1936 - 08-14-2018
Dumbkoff!
I had 2 caps on the volume pot switched. I pulled out my spare chassis which is in pieces, but the connections around the pot were intact. Discovered through eyeball comparison, I had switched 2 connections.
Needs alignment on the SW band, and a little cleaning up, but it works and sounds great!
[Video: https://youtu.be/zEwAlIoXs8Q]
RE: Philco 38-7 - PhilcoPhan1936 - 08-14-2018
The cabinet will get a total refinish in the future, and the cone pre-sets will be done at a later date, but it is back in the cabinet. A rubdown with Howard's Restore-a-Finish, and a new grill cloth, and it displays -and plays well- for now.
[Image: https://farm2.staticflickr.com/1839/42232423650_71497516fd_z.jpg]
RE: Philco 38-7 - PhilcoPhan1936 - 08-27-2018
Well, it's giving me grief again.
I turned it on to listen to last week, and it again was not receiving. not even static, after it was up and running sounding great. The 6F6G tube (output) tests low, but I don't think it's low enough to konk out. I'll run some tests Monday. I'm wondering after the mis-wiring, a component failed, it just took a few days to do so.
Will report back. I plan to go back through and inject a signal at various spots as suggested and see what comes through...
RE: Philco 38-7 - PhilcoPhan1936 - 08-27-2018
Well, I worked on it today. Checked a few things under the chassis. Nothing odd or dead or open, so I pulled tubes and started testing.
The 6F6G output tested low: 1200/2000. I got lucky and found one that tested 1800/2000, so in it went.
The 6J5G 2nd Det/AVC tested low as well: 2000/2600. Again, found a replacement that tested 3700/2600, so in it went.
The 6A8G, 6K5G and 5Y4G checked out ok.
That left the 6K7G. I went to remove the shield, and the tube popped. The shield was too tight on it, and it broke.
I managed to get the shield off, but the tube bit a finger in trying to unplug it from the base. I guess it was a vampire tube and needed some blood.
So I have no idea what it tested at.
I punched the tube into Radio Museum, and found it was used in a Philco 37-61B Late Tombstone I have that sits on a shelf for later restoration.
I pulled it, and It tested strong at 1550/1450, so in it went.
Turned the radio on, and it's back to life!
So I guess it just needed some blood.
Or a replacement 6K7 or 6J5 tube.
Will put it back together tonight, and dive back into a Zenith repair job.