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Model 96 Restoration - Printable Version

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RE: Model 96 Restoration - rfeenstra - 12-03-2017

After checking the info on Philco speakers, It looks like both sides of CT are way out.  Primary resistance should be about 550 ohms plate to plate.

RE: Model 96 Restoration - Electrothaumaturgist - 12-03-2017

Excellent work!!!   Icon_biggrin

RE: Model 96 Restoration - rfeenstra - 12-04-2017

Well, I fired it up and it works!  The transformer sizzles and fries through the speaker but gives about 150v on one plate and 250 on the other.  Another resistance measurement of the primary showed NO continuity!  I assume the the high voltage  is working through carbon tracks between the ends of the broken wires.  And the sizzle is arcing across the break.  Anyway it worked long enough for me to check voltages, bias voltages, etc.  Interestingly, I had 2 24A's fail during the testing causing me some head scratching.  I lost my bias voltages and finally found 1 24 had shorted from filament to cathode.  Then the radio quit working and eventually was surprised to find about 70v on the grid of one of the other 24's.  Thankfully I found a 124 Arcturus and another 24A in a box of old tubes.  They worked.  I was actually quite surprised at the sensitivity and selectivity with about 40' of antenna in the basement.

Now to repair the OT, cleanup the bottom cover and the tube shield.  Then, start on the cabinet.  I'm not a big fan of finish work! There is a shop that does a lot of radio cabinets in Grand Rapids, MI about 15 miles from here.  I may see what he charges, but I'm afraid I don't want to get a lot tied up in a common radio.  Golden Radio Service (goldenradioservice.com) sends his restorations to this guy for refinishing.  Golden Radio Serice is about 10 mile from me.  Never knew he existed.  I may call him to see if he has an OT for this radio in his junk box.

RE: Model 96 Restoration - Arran - 12-04-2017

It sounds like it's time to pull the power transformer and have a look at the leads, they may have some breakage in the insulation, and in the wires themselves that may be causing shorts, barring that there may be some other fault like a shorted bit of hookup wire elsewhere, or a wiring error. It's unusual to have a failure in most Philco power transformers without an external cause.
 The model 96 was a screen grid tubed TRF set, prior to the 1931 model year this was the top chassis that Philco produced, it even has AVC, so they were good performers. The main issue with TRFs is dial tracking, there is just no way to get every station spot on, which was why many of these radios didn't even denote frequency on the dial, just 0-100.
Regards
Arran

RE: Model 96 Restoration - rfeenstra - 12-04-2017

Thanks Arran.  right now I'm working on solving the output transformer issue.  However, having 2 tubes fail at almost the same time is suspicious, especially with the way they failed.  I will probably do what you said!

RE: Model 96 Restoration - rfeenstra - 12-12-2017

The output tranny has been rewound and the radio is now working wonderfully.  I have temporarily reinstalled the radio in the unrefinished cabinet and am listing to it as I type this.  It workes surprisingly well not being a superhetrodyne radio.  I really didn't know what to expect as this is a new experience for me with TRF receivers.  Late 1920's people had vairly reasonable radios to listen to even with RCA hording the superhet technology.  Sensitivity and selectivity are reasonably good.  Now to refinish the cabinet. That part I don't look forward to.  So far, though, it's been fun! I find, though, that the background noise is less on the Superhet radios I listen to. I don't know if this is characteristic of TRF radios. And Arran, Tracking is certainly not perfect, but it is close onough.

Thanks for all of your help in this project!

RE: Model 96 Restoration - rfeenstra - 12-12-2017

The 96 has been playing now for a day or 2.  2 problems for me to ask questions about:

the speaker cone was torn which is really not that much of a problem.  However, it is warped a bit.  One side is farther down in the "basket" than the other causing the voice coil to be crooked in the gap.  I can't hear it at normal listening volumes, but at very low volumes, I can hear what i think is the voice coil rubbing.  have any of you worked to try and straighten out the cone?  Perhaps my only option is to attempt a recone.

Second, and this is a repeat question, is there a way to "re-carbon" a volume control?  the specs say the volume control should be 500K.  Mine measures 3.2 meg.  As I suspected, most of the volume control happens in the first 1/3 of the travel.  I like the elegant mechanism in the control and would like to keep it.  How was the resistance element laid down in the first place?  Can it be duplicated?

RE: Model 96 Restoration - morzh - 12-13-2017

This series of radios has an interesting volume pots that have cylindrical resistive element and a brass wheel for the wiper.
Mine was fully open.
Unfortunately there isn't a good way to recarb pots. Whatever people try is unreliable.

RE: Model 96 Restoration - rfeenstra - 12-13-2017

So the solution is to stuff a standard control inside the original by removing the "elegant" mechanism?

RE: Model 96 Restoration - morzh - 12-13-2017

I just put a regular pot inside with the same parameters. Without re-stuffing.

RE: Model 96 Restoration - rfeenstra - 12-13-2017

Thanks!