1936? model 84 resistor - Printable Version
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1936? model 84 resistor - brownie45 - 01-22-2013
Working on my 84 Philco, & am wondering about #12--a 16K resistor
part #7500. It measures 20K, & needs replaced. I looked in the resistor cross reference & it calls for 3 watts. The resistor that is in question looks like it would be on the order of 50 watts--3/4 inch dia. by 3 inches long. Does anyone who has knowledge of these 84's know if 3 watts is adequate?
Also, the alignment/ operating instructions call for a fiber alignment tool to adjust the compensation caps on the chassis rear panel. What can be used in this adjustment--I would assume non-ferrous?
Sorry for the long post. Thank you for any info. Jim
RE: 1936? model 84 resistor - Ron Ramirez - 01-22-2013
Hi and welcome!
Bear in mind that the old "dog bone" resistors were MUCH larger than modern equivalents. 3 watts is adequate. Don't go any lower in wattage! If it makes you feel better, use a 5 watt replacement.
The original alignment tool was made of Bakelite. Replacement alignment tools made of plastic were sold by Antique Electronic Supply once upon a time, but they quit selling them about the time they switched owners and shifted their focus to the guitar crowd.
Some folks have made their own from thick, stiff (not flexible) plastic tubing, somewhat larger than 1/4 inch. The body of an old ball point pen is ideal for the job. Heat a 1/4 inch hexagonal piece of metal such as an Allen wrench, when hot insert into the plastic tube. Let cool and separate. Voila, instant Philco alignment tool.
RE: 1936? model 84 resistor - brownie45 - 01-22-2013
Thanks for the info.
Is the 4 meg. resistor mounted in the IF transformer pretty reliable or
should it be checked also? Hate to get into the IF if not needed.
How much of an antenna should this unit have? I'm assuming a
good ground is mandatory.
Is the 2 section electrolytic filter re-stuffable, or do you just put
new singles under the chassis? The filter looks rather hard to re-stuff.
Thanks again. Jim
RE: 1936? model 84 resistor - Radioroslyn - 01-26-2013
Hi Jim
You can measure the grid leak resistor without taking the IF can off. Measure from the grid cap to the IF trimmer. As for the ant the longer the better.
Terry
RE: 1936? model 84 resistor - Ron Ramirez - 01-26-2013
Moved to "Philco Electronic Restoration" since we're talking about repairing/restoring a set.
That grid leak resistor will measure 4 meg., or even higher. I can tell you from personal experience that it will need to be replaced. And you want to replace it with a 2 meg resistor for best performance.
The resistor is mounted at the very top of the IF transformer, so it must be removed from its shield can.
What you will need to do, to keep from harming the IF transformer, is to *very carefully* clip the leads of the old resistor right against the body of the old resistor, leaving two pieces of wire still connected to terminals on the IF transformer. Now take your new 2 meg resistor and wrap each lead on each of the short wire stubs you have left from the old resistor. Solder in place with a low wattage soldering iron and replace in the radio.
Do not try to unsolder the old resistor from its terminals, cut the resistor leads off even with the body of the old resistor instead. Don't ask how I know about this...
RE: 1936? model 84 resistor - Ron Ramirez - 01-26-2013
Oh, and yes, the two section electrolytic is restuffable. It's a bit of work - the old "guts" have to come out, and will have to be removed with help from a heat gun and a few choice words.
Don't burn yourself!
RE: 1936? model 84 resistor - brownie45 - 01-26-2013
Thanks for all the info. Just checked the grid leak, & it is open.
Half watt should be adequate? Is the .0014 cap in parallel
with the 6K 1 watt a mica, or is it a "micamold" cap [which
should be replaced]? Appreciate the help. Jim
RE: 1936? model 84 resistor - codefox1 - 01-26-2013
Yup, recarbonate and recap all.
RE: 1936? model 84 resistor - Ron Ramirez - 01-26-2013
1/2 watt is fine for that 2 meg resistor to install on the IF transformer in place of the original 4 meg resistor.
The original .0014 uF cap was mica, and if it has been disturbed, then it should be replaced. Use a silver mica (preferred) or an NP0 ceramic (acceptable) as a replacement.
RE: 1936? model 84 resistor - brownie45 - 01-26-2013
How close to .0014 does it need to be? .0015 O.K.?
Thanks for all the help. This is my first Philco
set, so I have lots of questions. Jim
RE: 1936? model 84 resistor - Ron Ramirez - 01-26-2013
.0015 is probably close enough for gubmint work.
RE: 1936? model 84 resistor - Radioroslyn - 01-26-2013
150pf is fine.
Terry
RE: 1936? model 84 resistor - Ron Ramirez - 01-26-2013
Actually, 1500 (not 150) pF. 150 pF = .00015 uF, 1500 pF = .0015 uF.
RE: 1936? model 84 resistor - brownie45 - 01-26-2013
Thanks fellows.
RE: 1936? model 84 resistor - Radioroslyn - 01-27-2013
Sorry I'm seeing two many zeros.
Terry
Don't get old you won't like it!!!