Thread Rating:
  • 1 Vote(s) - 5 Average
  • 1
  • 2
  • 3
  • 4
  • 5

Philco model 70 rebuild - by Tim P.
#51

I spent a couple of hours doing some careful checks. The cap in question on the tuner has a fiber washer under the other washer. I did some voltage checks on the 1st det and the osc tubes. I can PM with everything if needed, but the most obvious 'oddity' is the voltage on the cathode of the 24 1st det tube. When the radio is in the good part of the range, where it picks up, the voltage sits about 8v. I can adj the dial from 55 up to where it cuts out - same, that is, until I hit the place where it goes bad - then the voltage jumps up to 12v, and climbs to 24v as I tune all the way up, drop back, it falls until it hits the working part, then stabilizes at 8v again.

Now ... the odd part. I found if I turn the volume down until I can barely hear, I can get solid tuning up all the way to the top! It's when I start to turn up the volume, when I hit a point, it begins to oscillate and cuts off. The voltage on the cathode of the 24 also jumps at the point it begins to oscillate (and becomes microphonic). If I turn back down, it clears up. Also, the higher I turn the volume, the lower the freq that it starts to mess up.

I swapped the 27 with very little change (I am still waiting for my new one to show up). When I swap the 24 with a new one, the point I can turn up the volume lowers. I tried a weak 24, and couldnt get anything but static. I double checked the coils in the circuit. Also resistors, which are a little off, but not a lot. Also have voltages from the bias resistor. So, somehow, the volume control (checked also) and tuner and this problem are connected. I also want to comment that this is the area where a cap (#12 see my 2nd pic in the thread- I believe it may be mislabeled as #5) was replaced - years ago in looking at the style, so I believe this problem has been with this radio for quite some time - maybe even since new. This one has me scratching my head... got to be some dumb, simple thing I am overlooking. Any thoughts?

Sorry for the "book" ... just hoping someone can help me solve this mystery.

If I could find the place called "Somewhere", I could find "Anything" Icon_confused

Tim

Jesus cried out and said, "Whoever believes in me , believes not in me but in him who sent me" John 12:44


Messages In This Thread
Philco model 70 rebuild - by Tim P. - by TV MAN - 01-29-2014, 11:46 AM
RE: Philco model 70 rebuild - by Tim P. - by TV MAN - 02-22-2014, 01:45 PM



Users browsing this thread: 14 Guest(s)
[-]
Recent Posts
Shadow Meter Bulb
Phorum members, I am trying to find the bulb # for PHILCO Shadow Meter part number 45-2180 that is from a 37-640 chassis...georgetownjohn — 06:53 PM
Philco 41-608 changer coupler
3D-printing...short of machining, of course. Or molding.morzh — 05:20 PM
Philco 41-608 changer coupler
Thanks, Morzh. That solves the issue of the rubber pieces. Now, I need to find a way to replicate the pot metal piec...alangard — 05:07 PM
12' Philco
If it is 12', either Kareem or Andre would have to jump pretty high to look at the front panel. Kareem would have an e...morzh — 01:48 PM
12' Philco
And here's a story about the tires on the truck. Same "no-stoop" guy must have installed these! Take care a...GarySP — 01:17 PM
Hickok AC51 tube tester
I think they have only shown the secondaries of the transformer. Two of them feed the rectifiers' filaments.morzh — 12:58 PM
IF can wire size and Rubber mounts?
Arran If the wire inside cans is the gauges you mentioned, the sole reason for that would be mechanical, to stiffen t...morzh — 12:56 PM
12' Philco
Rod, Yes, I know, but the Giant Philco is not around anymore either, so I go by whoever was alive fairly recently. H...morzh — 12:54 PM
Hickok AC51 tube tester
Absolutely no one is going to reverse engineer that circuit. Even the iron core is missing.RodB — 10:37 AM
IF can wire size and Rubber mounts?
Thanks to both members for your help regarding wire and tuner mtg supports. regards--Johngeorgetownjohn — 09:33 AM

[-]
Who's Online
There are currently no members online.

>