update, got a first coat of Maroon on the Escutcheon assembly plastic body, i used maroon because it's a bright lovely color but in line with the spirit of the original purple plastic color used for knobs in these old trucks. painting this plastic allows me to color match it to the control bushings behind the knobs, it protects the plastic from further UV damage, and covers up existing damage allowing me to reuse the original. i also painted a reproduction escutcheon to see if i like that one more when i'm doing the final fit.
The steel housing is ready for paint, i'm going to paint it inside and out, originally it was not painted inside. I masked off a few places where i want metal to metal contact with the guts later on. if i had a better housing i would not use this one, it's in bad shape, i suspect it was left outdoors for decades. i cleaned it up, straightened it up and fixed some of the damage on it the best i could, hopefully it will turn out well. -s
hi everyone, here is an update on my radio project, now that fall outdoor activities have ended i can resume working on my inside stuff.
i painted the housing Rust-Oleum Brown (210880 Hammered Metal Finish), i was gonna use the copper hammered finish but it seemed a bit too bright this brown looks very satisfactory for me. photos attached showing the masked areas and how it turned out, paint really does hid the many imperfections
i may wait to glue on the reproduction decals until i'm ready for final assembly that way I don't damage them when i invariably have to take something apart many times to make assembly corrections.
All the misc. riveted bits go into the chassis at this stage, I don't want to be driving rivets home when there are electrical parts or transformers installed later on.
Cleaned up the excess zinc plating on the holes and edges of the chassis. The vibrator clamp will be replaced as it has broken tabs. The new one will be riveted with tiny steel rivets in place of the spot welds in addition to the socket rivets which go through the clamp, chassis and socket. I would not recommend dip galvanizing, it's a pain and not original. It would be better to spend more time getting the electroplating to work out as it was originally done, but getting the inside corners to plate is difficult. I will live with this learning experience for now on this radio.
I riveted the tube sockets back in using my handy small engine valve clamped into my table top vise. Some insulating papers were not the best shape, i found a very similar cardboard at my local junk store in San Jose Cali. If anyone is near the bay area, check out Excess Solutions, you will spend a whole day rummaging around
One of the wires had broken off the audio transformer, the remaining were not looking good. Carefully took the transformer apart to solder intermediate 30 gauge wires onto the tiny input side windings, these wires are in turn soldered to the larger wires that exit the transformer.
I used friction tape to wrap the transformer, it can be locked in place by applying cyanoacrylate to the tape ends. Once installed onto the chassis it is soldered in place on it's folding tabs. There are only 3 wires on the audio transformer because one side of output is tied to chassis ground. The speaker plug will return speaker current back to chassis ground at the speaker plug.
While soldering big stuff with the propane torch I also installed the triple electrolytic capacitor. The capacitor body is the common terminal of the electrolytic. At lease one mounting tab must be soldered to the chassis to ensure a good connection to ground. I often use tinfoil as a heat shield when soldering this way, the torch will quickly burn things or cause discolorations if not contained.
The power transformer also gets one edge soldered to the main chassis. The center tap of the input side of the power transformer is tied to chassis ground internally; this soldering is necessary to ensure the best performance from the power stage.
update Without burning my fingers... i have managed to install all the main chassis components. It's starting to look like a radio again!
Put fresh wire on the I.F. transformers, the old wire was faded and very oxidized internally. The painters tape is to protect the parts during assembly. I used colorful red shrink tube on the component leads in place of the original black cloth tubing which has all gone hard, i like the new red look, if someone prefers black that's easy too.
Most of the new resistors are now metal film type which are more stable and lower noise than the original carbon composites; these are likely overkill for this application, but the absolute price difference is not significant so why not splurge (pennies) on better parts right?
The large circuit capacitors are mostly PP or PET types that I got at the local junk store. As long as they have the correct value and sufficient voltage ratings that's all that matters for the most part. All trimmer mica caps are original, they will outlive modern civilization. I did disassemble some partially to clean them, but that was not electrically necessary, cosmetic only.
A sharp eye will notice i added a capacitor across the vibrator pins and also two on the main power input under the power transformer. The vibrator capacitor will help save the points inside the vibrator, this capacitor is standard on the next generation radios that came after this design. The bulk capacitors are to help with incoming noise from the vehicle. These locations likely would have had a capacitor when the radio was designed, and then they were omitted along with other parts we will never know about in order to reduce cost. -s
Now that the main chassis and tuner unit are complete, i will require a speaker to connect to them when i do the alignment. So it is time to tackle the speaker.
This radio came with an original electro-dynamic speaker, part number 7255903, this one is completely rotten and frozen with rust and dirt. A side note - There is some evidence that later on these radios came with a PM (permanent magnet) speaker. If you find a PM speaker (possibly part 7256355?) in your radio it could be the original too. If the pole magnet is too weak you can order a replacement magnet when rebuilding a PM speaker.
After carefully extracting the voice coil (because i might reuse it), I pressed out the pole piece. It presses out relatively easily from the back side towards the front while supporting the top plate with a large socket or pipe. Once the pole is out, the field coil slides out with the cardboard shims and the copper plate. I am not certain about the thick copper plates purpose. Either is is just a gap filler or the designers were getting fancy and thought this plate could be a 1 winding shunt for any AC ripple current presented to the field coil. Either way, it will be going back in, it's 1/16 thick and is needed to keep the field coil tight.
The original voice coil seems re-usable, however the paper may continue to warp so i will order a new one and decide which to Using paper shims to fit the original voice coil snug onto the pole I measured it's ID. (this way i know it's round and not oval) I will order a new mylar backed 1.000 ID voice coil which is probably what this original coil is suppose to be.
The spider cup needs to be about 2.2 inches in OD and about 0.2 inches high. The closest size to get is 2.171 OD x 0.197 height, I prefer to go the nearest size too small, as anything too big just never fits well and flat.
For anyone else who is rebuilding new or old speakers, my source for parts is The Speaker Exchange https://reconingspeakers.com The next post will be re-assembling the speaker, and i will include the specific part numbers for the replacement parts used. -stan
Last edited by 2ManyTrucks; Wed Dec 11 2019 08:49 PM.
speaker assembly follow up, i'll make two post today so i can put up more photos
material list: original speaker parts all cleaned up Devcon 18045 contact cement Devcon 20445 5min 2 part epoxy VC3000-4 - mylar/paper voice coil 1.000 ID, 4 ohms CS2171-C - spider cup 2.171 OD, 1 inch VC, 0.197 height W438001 - 6x9 cone DCP1100 - 1 inch dust cap (1.100" with down lip) R6X9 - mounting gasket for standard 6x9 PIGTAIL and SHIM KIT - included with most orders from the Speaker Exchange, these are the super flexible lead wires from the voice coil to the speaker terminals, and the shim kit has plastic card stock of various thicknesses to use instead of paper when spacing the voice coil onto the post.
The Speaker Exchange website has a good DIY section with photos on how to rebuild speakers. I had no idea how to rebuild speakers before a couple years ago, i just knew it was a thing that could be done, I've followed their guides and so far they all turned out great. https://reconingspeakers.com/faq/how-to-guides-2/ ……..How To DIY Recone with Unassembled Parts – most brand parts
What's specific to these Electro-Dynamic speakers is mostly the details of the field coil. I used more of the black friction tape as i did on the speaker transformer to wrap the field coil where it had lost the crumbling paper wrapping. Glue the ends of the tape with cyanoacrylate to keep it from unwrapping. The field coil slides in with it's copper plate and cardboard shims, then you press the steel pole piece back in from the front side of the speaker. The pole originally was a few thousands of an inch proud of the rear side, to get it there I first press it flush on the steel bed of the arbor press. Then the tricky parts comes in, the pole gap must be uniform, so measure it with a round rod/drill bit or any measuring stick of choice to check for uniformity. Assuming it's not prefect by luck this next step is how you center it and get the pole driven a tiny bit further into position.
With solid cardboard or leather supporting the speaker use a 1/4 inch steel punch and tap off center on the pole next to where the gap is largest. This action drifts the pole closer to the side you are tapping off center, closing the gap next to the punch (and opening the gap on the opposite side). Tap a bit and measure often, eventually you will get the hang of it and the pole piece will be reasonably centered. If it all goes bad, press it out and start again. If the pole is too loose, put a few dimples on the end that presses in and start again. There should be virtually no limits to how many times you can repeat this step to get it right.
Always test fit the parts before attempting glue or epoxy. The DIY guides cover the order of assembly quite well, but if you are not certain, plan it out yourself so that you know how all the steps will go before you start. I like to go slow, I leave the glue and epoxy cure overnight for a couple of the assembly steps. -stan