[NJARC] Philco 37-650 RF Question

[Harry Klancer]

Scott,

A couple of comments.

I don't think your resistor was orange-orange-grey
because 3300 Meg is not a standard value and
grey is not used as a multiplier anyway. Was it silver?
That would make the resistor 0.33 ohm - unusual,
but probably available.  If it was the resistor that
connects one of the output tube grids to the bias
voltage, which is the only place I see a 330K in the
schematic, and it was 0.33, I doubt any damage
was done. Anyone else want to comment?

As for the 9K. What using a 10K would do is slightly
raise the voltage at the 2nd grid of the 6A8
tube - probably 2 volts or so. This grid essentially
operates as the oscillator plate and runs at a couple
of hundred volts, more or less, so it probably wouldn't
make a lot of difference. It would also lower the screen
voltage of the first 3 tubes, but again, not by much.

Also, you asked about the wire before. Skin effect
at such low frequencies is negligible, so stranded
vs. solid doesn't really make a lot of difference.

Since it's not the 16A padder, have you checked the
dc resistance of the bc oscillator coil itself? That could
definitely affect the operation of the oscillator, although if it was
much out of spec, the oscillator wouldn't work at all.

Guess we're all still assuming it's the oscillator. Any
other symptoms?

                             Harry Klancer


At 02/26/2006 02:35 PM, you wrote:
>Visit our web site - See http://www.njarc.org
>_______________________________________________
>My problem with the resistor wasn't the age- I
>replaced all of them- it was the wrong band... It was
>supposed to be a 330k ohm, which has an
>orange-orange-yellow band arrangement. What got put in
>place was orange-orange-grey, or 3,3 and 8 0's- or
>3,300,000,000ohm! 3,300M ohm! Which was a little high
>resistance...
>
>I can confirm what you say about age, however: I have
>a box of NOS resistors from the 1950's/1960's, and
>while many are still very near correct, and within
>tolerance, many more are out of spec to a great
>degree. These usually donate their leads to little
>projects... These are all carbon comp resistors.
>
>Now, another resistor question. I replaced one of the
>power resistors, a wirewound 9k ohm/2watt(#61) with a
>combination: a 4.3k/2watt and a 4.7k/2watt, both metal
>oxide. I also replaced a neighboring(#60) 10k ohm, 2
>watt with a 10k/2watt metal oxide. I replaced #60
>again with a 10k/5watt wirewound power resistor, but
>not #61, as I could not find a 9k ohm. Would a 10k ohm
>wirewound power resistor be a better one to put in
>place, and could this have anyting to do with my
>problem?
>
>Thanks
>Scott
>
>--- Mbeeferman at cs.com wrote:
>
> > Visit our web site - See http://www.njarc.org
> > _______________________________________________
> > Having done a little research in this area, I tend
> > to agree with Jim.  A
> > rating is a rating, and functional differences
> > between a 1-watt carbon composition
> > and 1-watt film resistor should not exist.  Problems
> > at high frequencies come
> > into play only with wirewound substitutions.
> > I tend to believe that Bob's problem may have been
> > in another area.
> > The problem with carbon composition resistors,
> > especially NOS, is related to
> > how critical a tolerance is required.  The process
> > that creates carbon
> > composition resistors leaves them under stress.
> > Over the years, this stress is
> > eventually relieved (I won't go into the physical
> > details) and the resistor can be
> > left significantly out of tolerance.  As an
> > experiment, randomly select 10 NOS
> > carbons from your junk box that are greater than
> > 20-30 years old and take
> > some measurements...you might be surprised.
> > In any restoration project, I always`use the same
> > philosophy...it might take
> > some extra time, but it is surely worth it....
> > 1.  Verify what you install and don't depend on the
> > markings.
> > 2.  Verify what you remove (unless the component is
> > completely destroyed) and
> > ensure it makes sense with regard to the circuit or
> > the schematic.
> > 3.  Don't make any more than 3 replacements without
> > firing up the set to
> > ensure that you're not introducing more problems
> > than you're trying to fix.
> >
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> >
>
>
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>miserable creature who has no chance of being free, unless made and kept 
>so by the exertions of better men than himself." John Stuart Mill, 'The 
>Contest in America', Feb. 1862
>
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