Still having troubles

Still having troubles

Post by Art » Sun, 03 Mar 2002 01:03:58



             I'm still struggling with this
             Philco 50-920 I've been writing  about for what seems like
forever. I
             recapped it and had all but about 4 or
             5 resistors out of 15 replaced (13 out of 15 had really
drifted
             badly). Radio was playing loud and strong at that point but

             with some intermittent static and "cutting
             out." I decided to replace the remaining resisitors--what
was
             left were 4/5 resistors between the power tube and
rectifier and one across pins on the power tube (50L6).
             After completion with new resistors, fired up the radio. No

             static and no intermittent cutting out, but I lost just
about all the
             volume. Full volume setting on the switch and I hear a
normally strong
             station weakly. I checked tubes...still okay.

             I decided to check the resistors again for values. All okay

             except a 470K resistor between power tube and rectifier was
only reading
             about 343 ohms in circuit. I took it out of the circuit and
it checked
             at 460K. When I put it back in the circuit, I clipped one
lead
             (didn't solder) on the power tube. It read 460K across that
resistor.
             When I clipped the other lead on the rectifier tube lug
where it
             belonged, it dropped to that same little 343 ohm reading. I
think this is
             the cause of my diminished volume but I sure could be
wrong. It seems
             as though the 35Z5 rectifier is glowing too brightly under
power
             with that resistor connected.

             Anybody have a clue what I'm doing wrong? I know I've
changed
             something but I'm totally at the end of my wits. A radio
buddy
             looked at it with me last night. Neither of us can figure
it out. It's
             what I get for trying to tweak it some more I guess.

             Any help will still be appreciated.

             Thanks,
             Art

 
 
 

Still having troubles

Post by Bob » Sun, 03 Mar 2002 03:27:41


That resistor is probably across the output transformer and it's not your
problem.  Measure the tube voltages and see if things are where they should
be.

I think people tend to replace too many components when they restore radios
and end up causing more trouble by possible errors than they correct.  I
prefer to replace only defective or marginal components or those that
especially have bad reputations.  This includes elcetrolytic capacitors,
tubulars that seem to be leaking wax, and resistors that measure far from
their nominal values.  I also check and clean switches and sockets and look
for corroded solder joints and riveted or bolted parts.

Bob

 
 
 

Still having troubles

Post by Phil Nelso » Sun, 03 Mar 2002 04:24:32


My best advice is to do a very, very careful double-checking of every
component that you replaced, comparing every connection to the schematic and
checking things off on the schematic as you go. When you replace a lot of
components, as Bob suggests, it is so easy to make just one little mistake.
"Close doesn't count in this game," as the saying goes. A wire may go to a
nearby terminal instead of to the right one. A wire may get pushed over so
that it shorts against something. You may have misread the value on the
schematic or on a component. You may have made a bad solder joint or dropped
a blob of solder into a place where it makes a short. That's especially true
when you replace more than one component at a time. My practice, which is
slow, is to replace one thing at a time and then test the set. Replace one
more component, then test the set. If things suddenly get worse instead of
better, you have only one place to check!

Good luck.

Phil


Quote:
> That resistor is probably across the output transformer and it's not your
> problem.  Measure the tube voltages and see if things are where they
should
> be.

> I think people tend to replace too many components when they restore
radios
> and end up causing more trouble by possible errors than they correct.  I
> prefer to replace only defective or marginal components or those that
> especially have bad reputations.  This includes elcetrolytic capacitors,
> tubulars that seem to be leaking wax, and resistors that measure far from
> their nominal values.  I also check and clean switches and sockets and
look
> for corroded solder joints and riveted or bolted parts.

> Bob