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 Post subject: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Tue 28, 2021 9:26 pm 
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Joined: Aug Mon 11, 2008 1:01 pm
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Location: Lancaster, PA 17601
I have a few of these that obviously are in need of replacement after 100 years!
I want to maintain the originality of the sets, so I'm curious what others have done to replace this 1 mfd common capacitor in early 20's battery sets?
It is sealed and not wax-filled at one end, so I don't know how to get the guts out of this without damaging the case. I also can't hide a new one, since these lay on the mounting board for all the other components.
I think I would also need to use multiple smaller value (Maybe 0.1mfd) capacitors since I think the diameter of a 1 mfd would be too large. THe physical size is 4"H x 1-3/4"W x 1/2"D.
Any recommendations are greatly appreciated.

Thanks
John


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20210928_160658.jpg
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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Tue 28, 2021 9:43 pm 
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Find another brand of 20's era, flat, canned cap and re-stuff that. There are new oval wound caps that can solve the can problem. May have to use vendors like Mouser, Allied, Farnel/Newark.

You can fake a label if need be if the label is missing or 'shop a scan of a label.

That cap can looks typical of RCA and Stromberg-Carlson, likely a few others.

Kudos in trying to keep repairs authentic.

IMHO no harm in authentic repairs with parts from the 20's rebuilt...

Chas

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Tue 28, 2021 9:56 pm 
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Location: Lancaster, PA 17601
Thanks Chas!
I wasn't worried about getting a replacement to fit inside, It was the getting inside part that worried me. Where these (3 in different sets) are located, the size is somewhat restrictive. I may have to purchase some other 20's era cans, since I don't think I have anything similar.
These are in 3 different Electric Equipment Co. Wenger's Super Receiver sets. I plan to post some other requests for information related to these later. So I'm trying to keep them as original as possible.

John

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Tue 28, 2021 10:08 pm 
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jjfritz wrote:
Thanks Chas!
I wasn't worried about getting a replacement to fit inside, It was the getting inside part that worried me. Where these (3 in different sets) are located, the size is somewhat restrictive. I may have to purchase some other 20's era cans, since I don't think I have anything similar.
These are in 3 different Electric Equipment Co. Wenger's Super Receiver sets. I plan to post some other requests for information related to these later. So I'm trying to keep them as original as possible.

John
Like a LOT of 20's era off brands, data is either scant or non-existent.

Post some images of the problem areas and closeups of the cap.. It is a "B" bypass and can be located in other ares, Generally a Pacent, Fletchthiem, Dublier, Aerovox, Tobe all made a smaller 1 mf cap some even had a 2 mf cap.

Some close up images of that cap will reveal how to get inside, if need be...

Chas

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Tue 28, 2021 10:29 pm 
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Location: Boston, Massachusetts
I have a Vishay 1UF x 250V mylar box radial cap, has short leads $5ppd in US if you want one (this will fit right in). 75 cents each additional one. Also have a couple NIB Pilot bypass caps not sure what condition they are in.

Metallized Polyester Film Capacitor (Non-Inductive, Low Self Inductance, flame Retardant Encased) MKT. are non-inductively wound with metalized Polyester dielectric / electrode and copper-clad steel leads encapsulated in a plastic case sealed with epoxy resin.

Getting those out are easy, just heat up the can and pull it out,loosening up as you go with a knife. Turn on the oven,put over the heat vent from the oven on a piece of aluminum foil. Propane torch will work as well.

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Tue 28, 2021 11:27 pm 
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Location: Long Island NY
First off, it is not a foregone conclusion the capacitors are bad. 1920s paper capacitors are generally not impregnated with oil or wax, so they may still be fine unless they were under water. The 1930s and later "midget" tubular paper capacitors we all know and love (?) so well needed oil or wax in the paper so they could be tightly wound on semi-automatic machinery. That oil or wax breaks down over time (ever see oil go rancid?) and that's what destroys the leakage resistance of the caps. Test the old caps before condemning them; you might save yourself some work.

It looks like you could heat that capacitor up enough to melt the pitch, and slide it right out of the can. Then it would be easy to hide one or more capacitors inside. I would not try to change the values of the capacitors. Just use whatever they used. 1920s battery sets are a lot more complicated than they look when you consider all the possible places feedback and oscillation could occur. Changing the values of capacitors could upset the delicate balance that was set when the radio was made.

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Tue 28, 2021 11:59 pm 
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Joined: Aug Mon 11, 2008 1:01 pm
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Location: Lancaster, PA 17601
Some additional information -
I included a top and bottom picture of the Capacitor. It is all metal, not wax or tar, and it appears to be sealed, either solder or a clear coating or both.
I also included a picture of it on the board. Directly above it is a rheostat I have removed (That's Another problem!), so the space between it and the capacitor is very little.
There were no labels on any of the three on these sets, so maybe a lower cost "generic".
The missing rheostat is supposed to be 250 ohms, but MANY of the winding have broken, requiring a new one, or re-winding. The wire is very fine (#32 Gauge), but I have ordered some and will give winding it a try. I have 4 that have the same problem.
I also need some RF transformers, but will put those is a separate post later. I don't have high hope for finding these, but I plan to give it a try.
Thanks for all the information so far from All.

John


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20210928_183054.jpg
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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Wed 29, 2021 12:09 am 
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Location: St. Louis, MO
jjfritz wrote:
I think I would also need to use multiple smaller value (Maybe 0.1mfd) capacitors since I think the diameter of a 1 mfd would be too large. THe physical size is 4"H x 1-3/4"W x 1/2"D.


Nonsense. You could get 1uF film or ceramic capacitors that would easily fit inside.

Seriously, you wouldn't believe how small they can make high spec ceramics now.


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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Wed 29, 2021 12:14 am 
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Joined: Aug Mon 11, 2008 1:01 pm
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Location: Lancaster, PA 17601
As I originally said, I wasn't really concerned about that, but I am concerned about how to get inside it, without damaging it.

John

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Wed 29, 2021 12:25 am 
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Put paint stripper or lacquer thinner over the last 1" of the connector end to get a lot the paint off. Use a large soldering iron and de-solder the connections that pass through the center of the insulator and free up the electrode wires. Use same iron with solder braid and de-solder the joint all around the terminal end of the end cap. Clamp the body so not to damage and apply heat all around the end cap, using a chisel shaped block of maple, tap off the end cap...

Warm the can all around and with long nose plies extract the windings. Apply more heat and clean out the can of all potting, do so with end cap too. Remove any excess solder used to secure the cap to the can on both the cap and the can. Re-shape the cap and can if need be and prepare to re-solder. Insert new cap(s) and connect to terminals re-solder, paint black lacquer.

In this application where no pulse noise is expected generic metalized caps are fine. These can be found with oval windings, O.K. to put several in parallel to reach desired MF. 400 volt units are O.K.

If the old windings have not been destroyed, Warm them to drive off moisture and use a AC bridge that may give a balance reading of the cap. I suspect any where from 1 to 4 mf, no more, even 4 mf is pushing it considering the package size and application.

The higher resistance rheostats and potentiometers often failed as the resistance wire of the time was prone to rust. If the "C" battery or any carbon/zinc battery was stored in the case, sal ammoniac fumes accelerated the rusting out. You may find the constantan wire may have the near correct resistance/foot, if you can get lacquer or enameled resistance wire all the better.

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Wed 29, 2021 12:41 am 
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Joined: Aug Mon 11, 2008 1:01 pm
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Location: Lancaster, PA 17601
Thanks Chas!
I'll give that a shot. Nothing to lose at this point, sounds promising! I have a couple additional units that are all the same, so I can practice on one, if necessary.

All the 250 ohm pot's have the same problem one is much worse, and looks like a porcupine! No C Battery in these.

John

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Wed 29, 2021 12:51 am 
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To expand on the suggestions, since you don't have a schematic for the set, and it may not be possible to find one, I would also suggest that you try to measure the capacitors before you open them. Unless a cap is nearly a short circuit you can still measure the values with an AC capacitor tester, as long as it has a power factor or dissipation control so you can perfect the null. Leakage may make a capacitor unusable in conventional circuits, but it does not change the capacity. Do not use a digital capacitance meter; most inexpensive ones do not have a way of separating resistive from reactive currents so they will give erroneous readings if the caps are leaky.

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Wed 29, 2021 2:11 am 
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Could you post more pictures of the set

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Wed 29, 2021 2:16 am 
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Andrew-
Absolutely. I plan to do that tomorrow. I will also include the schematics.

John

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Wed 29, 2021 7:13 am 
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If you look at page 18 of my Grebe article, I restored similar capacitors.

https://www.worldphaco.com/uploads/THE_GREBE_MU-1.pdf

But it looks like yours have a different top ( where the terminals are ) soldered to the body. So you would need to de-solder it as best possible, by adding fresh solder and using solder wick and a high wattage iron (Don't put a propane torch anywhere near it, the temperature is way too high and will destroy the insulation on the lugs). If you had a temp controlled oven you could heat it till the solder just melted, though that might be a bit harsh on the fiber insulating washers, so its better to try working around the top first to the the iron & wick.

Since modern film capacitors are relatively small there will be plenty of room in there. Once finished, you will need to rub the case down and re-spray it black to give it a new appearance. As noted in my article, don't be tempted to significantly increase the uF value, even if there is room, it can have some undesired consequences.


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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Wed 29, 2021 1:09 pm 
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Joined: Aug Mon 11, 2008 1:01 pm
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Location: Lancaster, PA 17601
Thanks Acornvalve! Very good article on the Grebe!!
I had previously also restored a capacitor similar to the one you show, and it was pretty easy. This one, as you indicated, is certainly a little different. I'll try some things and hopefully I won't damage the case. Thanks for the tips!

John

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Wed 29, 2021 2:31 pm 
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Joined: Aug Mon 11, 2008 1:01 pm
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Location: Lancaster, PA 17601
Here is some more information, hopefully addressing questions or comments previously -
I checked the capacitor using my EICO Model 950 RC Comparator Bridge and it was 1 mfd. Just for kicks, I tried to measure it with my DVM, Capacitance range, and it was not worthwhile.
I am attaching a schematic I revised based on the actual wiring of the M33 set, and pictures of the front and inside. You can also see the location of the Cap.
Curious on opinions on the type of circuit?
This particular set has all 3 RF transformer open. They are Mu-Rad T-11. The left side of the Inside picture has an extra tube socket laying inside. It is not used, but came with the set as I got it.

Thanks
John


Attachments:
M33 Back Loop Schematic.jpg
M33 Back Loop Schematic.jpg [ 821.13 KiB | Viewed 240 times ]
Wenger's M33 Front.jpg
Wenger's M33 Front.jpg [ 290.63 KiB | Viewed 240 times ]
Wenger's M33 Inside.jpg
Wenger's M33 Inside.jpg [ 530.03 KiB | Viewed 240 times ]

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Wed 29, 2021 3:42 pm 
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jjfritz wrote:
Here is some more information, hopefully addressing questions or comments previously - I checked the capacitor using my EICO Model 950 RC Comparator Bridge and it was 1 mfd. Just for kicks, I tried to measure it with my DVM, Capacitance range, and it was not worthwhile. I am attaching a schematic I revised based on the actual wiring of the M33 set, and pictures of the front and inside. You can also see the location of the Cap. Curious on opinions on the type of circuit? This particular set has all 3 RF transformer open. They are Mu-Rad T-11. The left side of the Inside picture has an extra tube socket laying inside. It is not used, but came with the set as I got it.Thanks
John
Not that it is a name of the circuit, it is "similar" to one of the ACME variations. Single circuit tuned front end followed by untuned RF stages. Note that the RF transformers may have broad response to low, medium & high portions of the BC band. So may be labeled as such. Without the "Q" of the loop, directly connecting an antenna & ground I would expect very poor broad tuning response from this set...

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Wed 29, 2021 4:21 pm 
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Location: Lancaster, PA 17601
Here are 2 of the earlier versions, both model M32's, but different circuit configuration. I did notice that the Mu-Rad RF transformers in the M33 were the same model, but the 1st had an "A", the 2nd a "B" and no marking on the 3rd.

John


Attachments:
M32 Early Top Loop Schematic.jpg
M32 Early Top Loop Schematic.jpg [ 788.18 KiB | Viewed 226 times ]
M32 Later Front Loop Schematic.jpg
M32 Later Front Loop Schematic.jpg [ 756.41 KiB | Viewed 226 times ]

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 Post subject: Re: 20's Battery Radio Capacitor Replacement
PostPosted: Sep Wed 29, 2021 4:46 pm 
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The Murad RF transformer design is broadband. So much so that "special" construction for portions of the BC band are not required.

In a "way" that is good because the internal design should be relatively easy to repair.

I have found with ACME RF transformers, the paraffin was acidic and corroded the copper windings. So when repairing, if potting is to be used to be sure it has a neutral Ph. This would be true of any compound used to re-pot. It is possible there is no potting in the Murad. What is important in RF transformer repair of this type is replicate the wire type and size, the number of turns and the direction of the winding... All of which is self-evident when disassembled, well and good unless the corrosion is so severe that the turns come off in small bits :roll: Then hope the transformers are alike and the others are not so bad. Recourse is to fall back on 20's era construction articles for RF transformers...

A somewhat more difficult challenge is to determine what the inductance of the loop is and create or find a loop of similar inductance.

Although loops were sold with taps for example the D.T.W loop.

https://www.radiomuseum.org/r/tobe_dtw_ ... tenna.html

and

https://radio-guy.com/product/large-dtw ... p-antenna/

I have the large model D.T.W. but it needs minor repair. I do have the correct base :)

It may be of interest to know that this radio does not radiate. It is not regenerative nor have an oscillator like a superhetrodyne.

Such a receiver has "value" for its user as it is not detectable in use and would not would disturb any other radio in the vicinity... To its detriment, it cannot detect CW.

chas

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Last edited by Chas on Sep Wed 29, 2021 5:08 pm, edited 1 time in total.

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