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

48-482- Weird Problem
#1

Hi Guys,
I've got a 48-482 that I received not working (just static) a few months ago. All caps and any questionable resistors have been replaced. All tubes have been double checked. It has been a fill in project. So far I'm just concerned with AM. I got into it again and this is what I found:
I get nice loud static with any type of antenna. Following the directions for alignment I am able to get a good tone at 455Khz and was able to align it. That's as far as it goes. Still static on any dial position. I tried to get a tone at 1000Khz so I set my sig generator and set the radio dial to 1000. Nothing. I tried it again but had the antenna wire connected to one antenna input. This is when the crazy stuff started. Instead of a tone from my sig gen, I picked up a local radio station. As I turned the dial on the signal gen, I was able to pull in all my local AM stations.
What do you think?

Thanks,
Eric

Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org

#2

I think the oscillator is dead. Check the coils. How about any mica caps in the oscillator circuit? These can and do go bad.

--
Ron Ramirez
Ferdinand IN
#3

Thanks Ron, I'll take a look. Is it best to just use an ohm meter to check the coils for continuity? Should they be disconnected from the circuit?

Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org

#4

Eric, the ohm meter is just fine and checking in circuit is usually fine as well. All coils should show a very low resistance.
Jerry

A friend in need is a pest!  Bill Slee ca 1970.
#5

Hi Jerry,

All of the coils are .1 or 0 ohms. My DVOM has a setting for checking caps but it doesn't appear to be very accurate. Should I be looking for an open, short or what on these mica caps?

Thanks,
Eric

Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org

#6

Either open, short, or leakage.

--
Ron Ramirez
Ferdinand IN
#7

Ron,
What's the best way to test for leakage?

Thanks,
Eric

Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org

#8

There are - or should I say were - capacitor testers on the market that would test for leakage, shorts, etc.

If it were me, I'd just replace the D**n things and be done with it. Others will chime in with their opinions...hopefully. Icon_smile

--
Ron Ramirez
Ferdinand IN
#9

Ceramic cap exposed to a reasonably high constant (not AC) voltage should exhibit practically zero current. The insulation resistance is typically in hundreds to thousands MOhms.
The datasheet will specify that for every type. Anything below that is leakage. An egregious leakage basically turns a cap into a resistor, which you do not want.
#10

Long ago, a mentor told me the best way to test wax caps and electrolytic caps was to remove them, hold them over an empty metal trash can and drop them. If they make a nice noise when they land, they were bad. Your coils look good to go.
Jerry

A friend in need is a pest!  Bill Slee ca 1970.
#11

And I can still make a fairly accurate voltage measurement holding the leads to my tongue.
The only problem is the range is limited to 10-12V. Icon_lol
#12

Agreed, capacitors, toss 'em. Easy and cheap enough to replace carbon resistors at the same time. Long term reliability and performance results.
#13

Every electrolytic and wax cap was replaced as the first step. Are you suggesting that I just replace EVERY mica cap?

Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org

#14

No, micas can be left in.

Papers and lytics have to go.
#15

They are all long gone. Any idea how to address my original problem?

Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org





Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Hickok AC51 tube tester
Note that no power cord, power switch, or power transformer switch are shown. That (along with my experience with full s...DaleHCook — 07:09 AM
IF can wire size and Rubber mounts?
A pair of wire strippers can give you an idea of what the existing gauge of the wire leads are in the IF can, I think it...Arran — 06:07 AM
My last cabinet for this year
Hello Dan, That is really beautiful what great looking radio you have ! I have friends who live in Calgary and the wea...radiorich — 01:51 AM
Philco Predicta Siesta picture over time getting dimmer
I found that the wire insulation was burnt.  The fly back needs corona dope! Why would someone put that there?Platinumblonde36 — 01:09 AM
Philco Predicta Siesta picture over time getting dimmer
This is what it looked like beforePlatinumblonde36 — 01:01 AM
Philco Predicta Siesta picture over time getting dimmer
Platinumblonde36 — 12:58 AM
Philco Predicta Siesta picture over time getting dimmer
Platinumblonde36 — 12:57 AM
Philco Predicta Siesta picture over time getting dimmer
I'm finding some strange things in my set and for the most part it's also original, so I need to start going over everyt...Platinumblonde36 — 12:55 AM
12' Philco
Not anymore Mike. Andre The Giant Born: May 19, 1946, Coulommiers, France Died: Jan 28, 1993 (46 years), Paris, Fran...RodB — 11:53 PM
IF can wire size and Rubber mounts?
Renovated Radios do carry what you need. As for the voltage, a wire should be at least 300V-rated.morzh — 11:13 PM

[-]
Who's Online
There are currently 4137 online users. [Complete List]
» 1 Member(s) | 4136 Guest(s)
Avatar

>