Philco 91 Speaker Replacement - Printable Version
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RE: Philco 91 Speaker Replacement - dconant - 11-01-2024
I intend to use another Philco speaker and add 2K resistor in series with the coil. The speaker I will use measures 1187 ohms. The coil in original speaker should measure 3275 ohms. Will this work once I get a new output trans?
RE: Philco 91 Speaker Replacement - morzh - 11-01-2024
It should.
Make sure your resistor wattage (I do not know what it should be as you need to look at the current that flows through it) is adequate.
The Hammond transformer will match just about any speaker to the output.
RE: Philco 91 Speaker Replacement - dconant - 11-01-2024
Thank you. Someone mentioned earlier that 5 watts should do. I have ordered some other stuff and included a 5 watt 2K. I have a 10 watt. I will measure the current draw once I get this working. I replace the E caps prior to firing up any radio. The trans has been ordered. I did some cabinet work yesterday out in the garage while we had a nice day. Needs a fair amount of veneer work. That will test my skills.
RE: Philco 91 Speaker Replacement - morzh - 11-01-2024
Replace all caps, not just the electrolytic.
Leave only mica caps, they should not be touched.
RE: Philco 91 Speaker Replacement - Arran - 11-01-2024
I guess I should clarify, it's possible that the filed coil on the original speaker, barring something like finding a dead short across the B+ on the other end, may just have a broken lead at one end, it's worth investigating. I can't remember what style of speaker the model 91 uses but in some of them the pole piece can be pressed out, and the bobbin with the field coil removed and repaired or rewound. This is easier to do on one of the older pie pan shaped speakers that the model 70 and 90 used, I don't know about the later 8'' pincushion shaped ones, on the 12'' console speakers the rear bracket and pole piece is held on by pins that can be pushed out once the cone is removed.
Regards
Arran
RE: Philco 91 Speaker Replacement - dconant - 11-01-2024
I did take the cone out but I still need to deal with the distorted spider. The voice coil was pushed out of the center piece for what looks like a long time so the spider now maintains that state. Don't know if I can get it flat again. Maybe I can put little weight on it and let it set for several days. Now that the cone is out I'm not sure how to get it back in without rubbing. There is no access to the center piece from the top to use shims. I can check for a broken lead. Might as well since I have nothing to loose at this point.
RE: Philco 91 Speaker Replacement - RodB - 11-01-2024
You can center the voice coil using 4 long 1/4 inch strips of paper placed in the gap opposite each other, then slowly drop the vc into the gap. If it's too tight to give you some cone movement use thinner paper. Make sure the voice coil wires are in the correct position for the OT. When you have some movement then secure the cone and pull out the strips. I just did one and was very satisfied with the results.
RE: Philco 91 Speaker Replacement - Arran - 11-01-2024
What I have used for speaker shims are thin strips of plastic cut out of rolls of 25 mm photographic film, though you could probably use any strip of stiff, but thin plastic, such as that used for baked goods in the stores, or used as windows in packaging, though the latter may be thicker then photo film.
Regards
Arran
RE: Philco 91 Speaker Replacement - RodB - 11-02-2024
Arran, it's not that simple. The spider is mounted in front of the voice coil/cone blocking access to the magnet pole. That's why putting strips of flexible paper in the gap before inserting the vc centers it, then you can secure the cone and remove the paper strips.
RE: Philco 91 Speaker Replacement - dconant - 11-02-2024
Here are some pictures to help show why this might not be possible.
RE: Philco 91 Speaker Replacement - RodB - 11-02-2024
That's what I'm referring to. In addition, that spider is made of a dense cardboard material which is 80 years old and getting kind of tired. The low frequencies are kind of muffled and highs are barely there. People have traced and replaced the spider with a stiff plastic one resulting in very improved response. The plastic is flexible enough to produce the lows and stiff enough to handle the highs.
RE: Philco 91 Speaker Replacement - dconant - 11-02-2024
Oh I was not aware the spider was responsible for that. Since mine is distorted I might try that. Once the coil is back in how do I get the shims out?
RE: Philco 91 Speaker Replacement - RodB - 11-02-2024
That's why you use long 8-1/2 inch paper strips. They radiate outward from the gap so you have access to remove them.
RE: Philco 91 Speaker Replacement - RodB - 11-02-2024
The spider holds the cone in suspension over the pole piece and the center of the spider is secured to the center of the pole piece to allow the cone to move freely.
RE: Philco 91 Speaker Replacement - dconant - 11-02-2024
Got it. Thank you.
It is going to be a while before I can get to this. But if I can't repair the field coil it may be a moot point. But would give me experience to try a new spider and put the cone in anyway. I have another speaker (Philco 89) where the cone is shredded, so maybe I could put the 91 cone in that basket.