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Model 95 wire resistor question - Printable Version

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Model 95 wire resistor question - Guest - 11-11-2005

I recently got a very nice condition model 95 Philco and everything looked to be in top shape. Most of the caps had been replaced alreeady, so I skipped the variac and plugged it in, only to find a big plume of smoke coming out beneath the smaller power x-former. I pulled the chassis and looked underneath and saw what appeared to be a type of wire wound resistor had fried. The resistor (if thats what it is) is open wire wound around a rectangular piece of some sort of laminate, roughly 1.5-2 inches long. It attaches to the main wire cluster that runs along the back of the chassis, but I'm clueless as to what the part might be, as well as why it fried. Pulling the power rectifier tube doesn't help. I have some pics of it but not sure if I can attach them (I'll try).
Any and all help is appreciated in getting this beauty up and running again. The photos are taken from the area directly under the power x-formers and tubes. Thanks in advance!

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- Ron Ramirez - 11-11-2005

Hi Flashback

From your description, it sounds like the dual bias resistor has died. This resistor has two sections of 70 ohms each.

While you're inside, check the very large resistor also under the chassis. Its value is 8300 ohms, and these resistors are usually bad.

You should obtain a copy of the service information for this set. I can get you started with a schematic:
http://www.philcoradio.com/tech/images/95e.jpg
http://www.philcoradio.com/tech/images/95.jpg

but you really need the under-chassis view so you will know which part goes where. I suggest you visit here to obtain the complete service info for your set at a modest price:
http://www.philcorepairbench.com/schematics.htm

Good luck.

- Guest - 11-13-2005

Could I substitute 2 70 ohm resistors, or do they need to be of identical design to the original? According to the schematics I have, the 1st resistor goes to E and the 2nd half goes to ground...or am I reading these incorrectly?

FB

- Ron Ramirez - 11-13-2005

Yes, you can use two individual 70 ohm resistors. I'm not sure at the moment of the wattage needed (taking a break from spraying cabinets, no time for calculations right now), but try 5 watts each as a start.

- Guest - 11-15-2005

I'm at a bit of a loss with this one. The resistor still works (although most of the structure other than the wire is carbon by now) and I can't see where the problem is. If I checked the center tap wire to ground, I see 70 ohms. I also see 70 ohms between the beginning of the resistor and the center, as well as 140 (give or take a few) ohms to ground ...this seems correct. I checked the 100000 ohm resistors where E goes into the filament, and it read 100K as it should. So...it seems I have no shorts to ground and I can't figure out why the resistor heats up so badly.
On a seperate note, I see two large resistors...one is roughly 800 ohns and about 2 inches long, while the biggest is at least 4 inches in length (biggest wire would item by far) and measures 8000 ohms (give or take a few) resistance. Is this the large resistor you referred to (that should be 8xxx ohms?). I look forward to any input on this problem. Thanks for all of the help to date!
On a side note, I replaced the resistor in question with a few 10 watt resistors and they too heat up quickly. Since it looks like the voltage comes out of the nearby transformer, could it be the x-former that is bad (although I know they usually die and not allow higher voltage thru)? The dial light lights up normally, I'm just at a loss to figure out why the problem is there since there aren't any shorts on the E line. Is it something so obvious I should shock myself a few more times for good measure? Icon_rolleyes The caps should be OK as most were changed with modern equivalents and they still store up a pretty good charge, even after powered off for a spell.

**********ADDENDUM***********

It doesn't make any difference if "E" is connected or the 45s are pulled, the resistors still get hot quickly. A local tech suggested I check "C" to ground, but I'm not sure which line it is as there are several caps in the area and its hard to see what is what. A possible shorted transformer was also mentioned as a potential problem, along with a shorted cap. I'm still getting nowhere.


Jim

- Ron Ramirez - 11-17-2005

Hmmm...something is causing resistor (49) to draw way too much current! In normal operation it should run cool.

Line "C" is the main B+ coming out of the filter network. A quick way to check this is to measure the resistance between terminal 9 of the large filter cap block ( 48 ) and ground, with the set UNPLUGGED.

Questions:
* Do you have the complete service info for this set yet?
* If not, have you contacted Chuck at the link I gave you above?

You are really going to need to see more than just the schematic; and you need the complete service data for that. I have the Model 95 manual (16 pages) in high-resolution PDF format; I can send it to you if you have a broadband connection (13 MB). If you're on dialup it is better to order from Chuck.

Let me know...

EDIT: Yes, the long ceramic resistor is 8300 ohms and the shorter ceramic unit is 800. If these measure okay, that's a very good thing.