[Arran]

I don't like using abrasives unless I have to, (rust) I start off with a stiff brush and a shop vac, and if it's still really grungy I have been known for washing my chassis with a solution of trisodium phosphate, and hot water, usually two tablespoons to the gallon. I do not immerse the chassis of course, I pour or spray the solution on, let it sit, work things around with a toothbrush, rinse with more hot water, and then let the chassis dry for a week or more. I should mention that I usually wait until the warmer weather to do this as things dry up faster without help.
Regards
Arran

[eewill]

I'm going to have to replace most of these wires. The cloth insulators are all extremely brittle. What gauge is used under here? It looks to all be able the same size. Speaker wire and power cable are larger though.

[morzh]

Most wires could use AWG24. This said, I have not seen one sold under AWG20 if one wants cloth-covered with the 600V rating.

So I use either this or AWG18 for filaments in all sets that drew lots of current.

[eewill]

@morzh Thank you. I'll add that to my growing list.

[MrFixr55]

Hi EEWill,

Sorry I have not been following the thread; I've been juggling chainsaws lately.

Since the amplifiers in the radio are not "Op Amps", they are not as complicated as the audio circuits in even a simple Op Amp such as a uA741. No inverting and non inverting inputs (except in a Push Pull output stage), no mirror current or constant current supplies, etc.

I echo all others who state to resist "just powering it up". Electrolytic capacitors used in the power supply go bad, either being "open" causing extreme hum or shorting, destroying the rectifier tube, power transformer, etc. Paper capacitors also can short, causing resistor burnout, tube burnout, etc. In addition, bakelite block #69 is a simple "EMI" filter cap connecting both hot and neutral of the power line to the chassis. A short in one of these caps may cause the chassis to become "hot" (120V above ground) causing a shock hazard.

The can of Electrolytic cap # 67 is isolated from the chassis. This is common in earlier sets where the cathode of the audio output is at chassis potential but the "B-" terminal of the HV supply is NOT at chassis ground, it is more negative than the chassis. This is to gain the correct grid negative bias but keeping the potential between the cathode and heater of the tube to be as little as possible. Considering the size of 10 uF 450V caps, these can be placed under the chassis instead of "stuffing the can".

Re the wiring, it doesn't really matter that the wiring is brittle. If not disturbed, the insulation will stay on. I have not had to rewire any radio with cloth insulation, including RCAs of that vintage. Rubber insulated wire from the very late 1930s and early 1940s is a very different case altogether. Leaving this wiring in place will save you much time. The only wiring that you may need to replace is the wiring above and outside the chassis.

Exact replacement cloth power cord is not available because it does not meet UL standards. There are many sources of wire on eBay of varying quality (and safety). When I was a kid, I remember rewiring my grandmother's crystal lamps, ca 1920. In the late 1950s, early 1970s, modern lamp cord with a silk like cloth covering was still available at almost any hardware store. This is no longer. I found this cable, with attached plug which will be period correct looking. It is the common UL listed 18 gauge SPT lamp cord with a woven jacket over the cord, so it should be durable and safe:
https://antiquelampsupply.com/products/m...-of-length

I am not listing the above as an endorsement; I am merely showing one style that is available. There are others available on other sites but some of these are all cloth insulation and are not UL listed.

If the plug is polarized, the wider prong is to Neutral and the narrower prong is to hot. (I'm sure that you know this; I put this type of info into my posts for beginners in the hobby without an electrical or electronic knowledge. who read this post.)

For replacing caps that are not part of a Bakelite "block" a fast but (IMHO) legitimate method is to cut the leads as close to the body of the cap or resistor as possible, bend a loop in the lead, clean the connection, and pass the lead of the new part through this loop. Loop the new part's lead, crimp and solder. If no need to rewire, this method saves time because you are not disturbing the connections at the tube sockets, which tend to be fragile. In your case, 'stuffing" the paper caps is likely not worthwhile, as these caps are already replacements and appear to be molded with paper labels. "Orange Drops", yellow mylar caps, etc. are all legitimate replacements. the latest and greatest resistors are the metal film type for 2 watt or less.

If replacing caps that are part of a Bakelite block, there are 2 methods. If just soldering the replacement to the terminals on the block, it is very important to disconnect the cap inside the block from the terminal. this can be done by passing a drill through the rivet. The more correct way is to hollow out the block. Here is a link to Morzh's technique which works very well:
https://philcoradio.com/library/index.ph...soldering/

The rectangular "cans" on the top of the chassis house the "IF" (Intermediate Frequency) transformers. These are tuned to the specific "IF" frequency by variable "trimmer" condensers (capacitors) whose screws are accessible through the top of the cans. 4 of the 6 screws are the trimmers; the other 2 hold the trimmer assembly and the transformer coils to the can. The coils of these "air core" transformers are usually I would leave these in place and clean as best as possible. Some folks in this Phorum have gone as far as complete disassembly of the radio and replating the chassis. For this first go-round, just try cleaning, using increasingly strong detergents and solvents until you find one that works. The environment of the radio will determine what type of gunk that is on the chassis. In one case of an AA5 chassis that was totally polluted by nicotine and mouse waste, I covered the holes in the IF cans, put it in the bathtub and totally bathed it in Windex and took the shower massage to it, then took the hair dryer to it and finally allowed it to dry on top of the boiler for a week before working on it. It was dry by the time I powered it up. BTW, the disgusting nicotine runoff was a good incentive to not smoke. Kitchen grease will come off with various organic solvents such as isopropanol, acetone, or even WD 40 wiped on and off.

Prior to cleaning with liquids, taking an air gun, leaf blower, etc. to the chassis may be helpful, particularly for the tuning capacitor (remove the dial to protect it. It is likely delicate and brittle. Again, please wear protection such as an n-95 mask, shower and change clothes after.

If dealing with mouse droppings, urine, hair or carcasses, please do wear mask and gloves and wipe down with disinfectants. Hantavirus (carried by mice) can be dangerous to humans. Even if you do not get sick from it, antibodies to hantavirus can cause false results on certain immunochemistry tests for heart disease, cancer, therapeutic drugs, etc.

One area of difficulty may be the tuning capacitor. The gunk on trimmers should be cleaned but before turning any screw, mark a point on the circumference of the screw and the can and count the turns clockwise till it is tightened. Clean the exposed edges. try not to bend the plates. The plates are aluminum and do corrode, causing threads that are almost like the stalactites and stalagmites in a cave. These can short the tuning condenser, thereby shorting the condenser. Symptoms including being unable to tune stations at a lower frequency than the point where the places touch. The bearings and vernier tuning device must be cleaned and lubricated also.

One thing I like to do with these radios is to add an "aux" or "Phone " input. Although this is a "mod". it is a "mod" that was commonly done during the period that the radio was used (date of manufacture until about 10-15 years later). this radio uses a 42 (6F6) audio output tube and an 8" speaker and is capable of a nice, warm sound when an external source (CD Player, MP3 Player, Bluetooth, FM converter, pre-amplified and equalized magnetic cartridge phone, etc.) is inputted to the radio. A transmitter can also be used, but there will be much less distortion when a direct input is used.

Do not let all of this discourage you. You already work on stuff much more advanced than this radio. I would repair and restore the chassis but not make the chassis a museum piece on the first pass. This will give you the satisfaction of getting the set to work. The cosmetics can come later, but this is your set, your rules and your procedures. I am sure that you will succeed!

Good luck with this restoration.

[morzh]

I second Mr.Fixr's sentiment about the wires being brittle: those that are not rubber-insulated, however brittle (not really brittle: they are hardened) will do just fine and, if not disturbed excessively, will serve another 200 years. They do not disintegrate.

This is especially useful as, 1) you get to keep the authentic look, 2) don't have to re-wire a...whole lot, 3) light disturbance, such as unsolder-cut-clean-solder back will do just fine. Just don't bend the rest with small radii. 4) there are radios like the early Philco models that use a cloth-covered wire bundle. Go try to get this one. And making a new one is a tall order. I always keep the originals.


PS. Many don't give much hoot about the cloth-covered wiring, and I absolutely have no problem with this. Whatever makes the radio work properly.

[eewill]

Thanks guys. I was considering stripping everything off and re-working the whole thing. I see "layers" of capacitors that need to be replaced. It looks like some are even underneath that board mounted off to one side. In addition to that, I was thinking it would be easier to test resistors as they come out of the circuit.

I'm still not sure how I'm going to reach everything, but you may have changed my mind on a complete rework. There are a LOT of components under there.

[eewill]

What is the recommendation for the speaker? I thought it was in OK shape, but it definitely has a fairly large tear in the paper. If I'm not trying to keep it all looking original, what is the most economical fix? Repaper, find a replacement, or rework a newer speaker into it?

[jrblasde]

Is there a piece of the cone missing? If it’s a clean tear and there’s no paper missing, I’ve heard of folks painting on a bit of rubber cement over the tear to fasten it back together. But if it is a large tear or you have pieces missing, you may need to re-cone it. There are folks around who have the skill. Turns out there’s a guy in the local Heartland Antique Radio Association club here in Tulsa who makes a living at all things speakers, including re-coning.

[eewill]

It's all there. I could glue it back together. It's definitely very very fragile. Is there anything you can do to "condition" it and maybe make it a little more robust?

[RodB]

Hi Will,

Whenever this subject comes up everyone moans when Rod responds. Here's what they're moaning about. The speaker is designed as a stiff cone to move in and out to produce the sound. If there's a tear or hole in the cone, the whole cone is not moving together. Hence, buzzing or distortion. Repair it with a similar material (stiff paper) using acid neutral adhesive (not necessarily necessary). The surround, however, is where all the action is. It's designed to provide flexibility doing all the bending and often is a different, softer material. Older speakers benefit from a coating of contact cement around the surround, it stays soft and bonds the fibers in the surround material. It will also add a little bass response to the speaker. I've done this to many speakers with good results. But, it's one of those things that you won't know what it sounds like if you do it some other way. This method always seemed logical to me.

[dconant]

I have and do use Weldwood contact cement. The same stuff I use to glue big pieces of veneer on cabinets. Works really well. It is pretty flammable so well ventilate and stay away from flames (water heater). Keep in mind the stuff is very sticky so once you apply it you can't separate the pieces.

Dan

[MrFixr55]

I don't know if the other folks approve of these methods. Yes, I definitely coat the corrugated section of the outer circumference of the speaker (the "surround") with a thin layer of contact cement. You can spread a little cement around the tear, place some toilet paper there as a patch and push it all together. When I was a kid, I would coat a weal cone with a layer of Elmer's Glue - All. This DID strengthen the cone, but I bet others are cringing as they read this. There are also spray contact cements. However, you want the stuff that dries. The stuff that stays sticky will attract dust.

Whatever technique that you use, don't cause the cone to warp. This may affect the centering of the voice coil, and rubbing of the voice coil on the pole of the magnet will cause distortion.

Hope this helps.

[eewill]

The Bakelite block #66 was stated as a 0.3 uF on the parts list. Taking it apart I discovered that it’s actually two 0.15 uF in parallel. I ordered the 0.3 uF without realizing it. I can think of a couple of reasons the parallel combination might be preferred. How critical is it? Could I just use the single 0.3 and be OK? I’m not familiar enough with the operation of radios this old.

[jrblasde]

Based on the schematic, it looks like it’s being used as one capacitor. You’ll be fine to use the 0.3 uF capacitor you bought.