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Philco 2W resistors mystery - morzh - 05-17-2014

Today I was repairing an 84 which is pretty much an 80, and the 2W 16K resistor was 12.8K. Unusual as typcally the carbon reistors go up in value.

This is the second timebI see this: the first time it was my 80 and it uses the same exact resistor, 2W 16K, and it was about 10K.

I never saw this type anywhere else so far, so these are my only two enounters and both were down in value.

Anything special about Philco 2-Watters?

RE: Philco 2W resistors mystery - codefox1 - 05-18-2014

Well just about 20% off, (16 vs 12.8 about par for the course for resistors not otherwise marked for tighter tolerence. The other one (10 vs 16) dunno. In either case, they are in the voltage divider, probably no noticeable effect in performance.

RE: Philco 2W resistors mystery - TA Forbes - 05-18-2014

I have seen the same thing more in the higher-wattage Philco carbon resistors than in the smaller rated ones. Why they decrease vice increase in value I do not know.

As a rule I replace any resistor more than 10% off. I figure that it will continue to change value as it continues to age.

RE: Philco 2W resistors mystery - morzh - 05-18-2014

Codefox

Yes there is an ffect: the upper resistor is 2W and it became 13K (from 16K). The lower is 1W and became 19K (from 15K). So, the ratio of 16/15 and 13/19 with the voltage of 240V will give us 256V vs 164V.

So, there is some, well, difference.

RE: Philco 2W resistors mystery - Ron Ramirez - 05-18-2014

For the past few years, I just automatically replace capacitors and resistors in the vintage Philco sets. The old carbon composition resistors are known to drift, either up or down, so I feel that I might as well avoid any issues by replacing them and being done with it.

RE: Philco 2W resistors mystery - Radioroslyn - 05-18-2014

I don't think I've worked on an 80 series Philco that I didn't have to replace all of the resistor barring the bias resistor at the ct of the power trans. All of them way out of spec.
Terry

RE: Philco 2W resistors mystery - codefox1 - 05-18-2014

Yeah. I fear I am beginning to sound like a drone, but if I'm going to spend a couple of hours on a chassis, I'll certainly replace all the small carbon resistors and all the caps. Guess I should learn from Ron and replace the 2 watt voltage divider resistors as well even if they are not crispy critters. Dunno what makes them go down in value, might be just initial low quality control or something else (resistance are futile?.) that hasn't surfaced in a while. Ideas?

RE: Philco 2W resistors mystery - Ron Ramirez - 05-18-2014

Right, Terry. When it comes to the 80, 81 and 84/37-84...in my experience also...I had to replace every resistor save for the bias resistor in order to get the radio to work properly. Who knows, it may have been an experience with one of those that made me start replacing every carbon composition resistor in every radio I work on.

Codefox, we posted at the same time...as for ideas, I can only repeat what I already posted above...it is wise to replace all of the carbon composition resistors in a set if you are going to operate it on a regular basis and expect its performance to be consistent.

RE: Philco 2W resistors mystery - PAradiogeek - 05-18-2014

I have noticed that most resistors seem to have drifted high over the years. That said, I have noticed that some resistors drifted low. I never noticed a pattern as to wattage rating or any other factor.

Personally, I only replace resistors that are more than 10% off nominal value. Hopefully this tactic won't bite me down the road.

RE: Philco 2W resistors mystery - morzh - 05-18-2014

Here's my meaduring resuls.

Load resistor of the 2nd det. 250k, filtering load res of the same tube, 10k, are OK.
I thought 1/2 W 6k resistor in osc feedback was OK, it measured 4.4K....then I realized nothing shunts it, bit it out, and it was 4.4K, so I replaced it too....another one that went down, not up.

RE: Philco 2W resistors mystery - GarySP - 05-18-2014

Just a question since this was brought up. Could the 50 or 60 years of dirt that builds up on a particular resistor possibly cause a tracking issue outside of the carbon resulting in a decrease in resistance? Any ideas? Take care, Gary.

RE: Philco 2W resistors mystery - morzh - 05-18-2014

No, usually it is not the reason.
It is structural / material degradation.

RE: Philco 2W resistors mystery - Jamie - 05-20-2014

I have never noticed a pattern either. I try to replace them all, but I am still acquiring a stash of 2W (or higher) resistors. They are not cheap and I can't find anyone who will sell a kit that contains different values.

RE: Philco 2W resistors mystery - morzh - 05-20-2014

Kits are expensive.

if you know values you want, just make a list and go to Mouser.

RE: Philco 2W resistors mystery - gregb - 05-20-2014

I just picked a whole bunch of NOS dog bone resistors and they were well stored and are in mint condition. I have gone through them and about 50% read right on the money within 5% of indicated value. The rest read all over the place but the trend I did notice was the higher values say 200k and up seem to drift up in value and the lower ones seem to have drifted down but neither is 100% true because some are opposite that trend. Not sure what to make of this as these have never seen voltage or heat of a radio.

Gregb