The PHILCO Phorum
Model 90 dogbones - Printable Version

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Model 90 dogbones - lasurveyor - 10-29-2017

Hi,

Just going to get started on a Model 90 chassis and see all of these cool looking cast end dogbone resistors but most of them way out of spec. Normally later radios will get new carbon comp resistors to replace the old like ones. Here I don't know what to do. New ceramic resistors would look pretty sad compared with these dogbones, but they've mostly drifted way off. I'm really not into the work of imbedding new ones into a cast. Maybe I should just put in the modern resistors and not worry about it?

Alan

RE: Model 90 dogbones - morzh - 10-29-2017

Steve here makes and sells (on eBay or you might ask right here) dogbones kits for pretty much every Philco radio.
Myself, I use modern resistors, they don't look as bad as modern caps, but if you are this particular- Steve's your man.

RE: Model 90 dogbones - klondike98 - 10-29-2017

Yes, email Steve to see if he has some to sell or you can see how he makes them and do it for yourself.  He has put the how-to info on the following thread in the Philco Tech Section:

http://www.philcoradio.com/phorum/showthread.php?tid=5501

RE: Model 90 dogbones - lasurveyor - 10-29-2017

Thanks for the response guys. Between casting new ones and just installing the modern resistors, I think I'll go with keeping it simple and just put in the modern ones without trying to hide or disguise them. It's just that those old cast end ones look too neat to yank.

Alan

RE: Model 90 dogbones - morzh - 10-29-2017

I keep those still within 20%.

RE: Model 90 dogbones - klondike98 - 10-29-2017

Yes as Mike says...often they are within spec so its worth testing them.

RE: Model 90 dogbones - lasurveyor - 10-29-2017

Yeah, you're right, I'll take another look at them and maybe some can be saved.

RE: Model 90 dogbones - morzh - 10-29-2017

Better yet, in some places the value is not that critical so even if a resistor is 50% or more out, it can still be used.

RE: Model 90 dogbones - Steve Davis - 10-29-2017

The resistors with the cast ends (I call them dumbbell style) seem to be slightly more stable than the wire rapped style, though we find plenty of both that are out of tolerance.  Philco used both styles, some times a mix in the same radio.

Steve

RE: Model 90 dogbones - morzh - 10-30-2017

Seems like the cast type disappeared fairly soon. I see them in 20-70-90 time radios but then I no longer see them.

RE: Model 90 dogbones - Chris h - 10-30-2017

Perhaps I am just different, but it seems that restuffing wax/paper caps, and remolding dog bone resistors is kind of deceptive. I know, it maintains the look, but who will see it, but another tech? Sure, I restuff the Bakelite blocks as it is more convenient than trying to add a terminal strip or adding the cap on the outside of the the block and breaking the old cap connections. I do restuff chassis mount electrolytics, when possible, as they are visible from the top side. But looking at it from the point of view of the next guy that might have to work on the radio, I would rather be able to see that the chassis has been gone thru, than pulling a cap or resistor and finding out it had been restuffed. I even go as far as putting a label on the chassis indicating that it has been updated with a date. Since I do these for myself and not for resale it is more of a reminder for me, more than anything else. I will leave the old resistors if still within tolerance, figuring if they made it this far, they must be pretty good.
My methods may not be the popular approach, but it works for me.

RE: Model 90 dogbones - morzh - 10-30-2017

Chris, as you might've noticed, we here do not turn up our noses to whatever way of reviving old chassis' as long as it is done in a safe and reliable manner; the degree of the authenticity is totally up to you. If it works, it works, and very few of us many years from the day of the final assembly will take it apart again to show our grandkids and say: see, these are the resistors and caps they used those days. But....just in case some are indeed this way, they do it.
The very fact that another radio gets to live and perform for another century or so is a beautiful thing, the caps being yellow or restuffed, and the resistor being dogbones or today's type.

RE: Model 90 dogbones - lasurveyor - 10-30-2017

Thanks for all of the comments. Myself, I generally enjoy tackling some pretty ugly messes and get the chassis and cabinet back as best I can hopefully saving the radio from being gone forever. They're not rare or especially valuable, the fun is in bringing them back to life. So I'm going to use modern caps and resistors that no one will see and hopefully have the radio looking and performing well. As I've been removing the dumbbell resistors I'm checking them and so far six of seven ran from 15% to 49% so I won't be saving any.

Alan

RE: Model 90 dogbones - morzh - 10-30-2017

Alan

Keep in mind, the resistors in tube schematics most often than not could be checked in-circuit (with the power down, obviously) before you de-solder them. It is due to the fact that the cold tube is essentially a bunch of open contacts with no conductivity whatsoever in between them, and so most resistors that in one way or another end up on some tube electrode with one of their pins are, in fact, have that pin hanging unconnected for the measurement purposes, and so can be measured in citu. This way you do not have to do any unnecessary soldering should you decide to leave a resistor in after it having been checked, plus the very act of the heating might introduce some damage to a resistor that otherwise might've been a perfectly good one.

RE: Model 90 dogbones - lasurveyor - 10-30-2017

Thanks so much for the info, always learning. I had already checked them and decided to swap them all out, everything gets disconnected restuffing the bakelite caps anyway. Not fully understanding things I was looking at them after removing them to see if the reading was the same and taking a closer look at the percentage of drift, more out of curiosity.

Early on I thought this chassis was untouched, probably because it still had original electrolytics in it (Sprague, not the copper ones, dang), but when I got started I saw that someone bypassed bakelite cap 23 with a 0.02 and in the process shifted around a half dozen resistors. I've had to take it slow and try to be sure that I'm putting things together per the schematic. Pretty happy with things so far, nice to have all of that elbow room in the chassis, easy to work on.

Alan