June 28, 2021 at 4:23 pm #17004
I received a Crosley 181 and am relatively new to radio restoration and am looking for advice regarding replacing duo caps. This radio has three duo caps and I have never come across this in my brief time since I took up this hobby.
The first pic is of an .006 / .05 cap #37 and #38 on the schematic and the second pic is of #19 and #20, a .1 .1 mfd cap. Someone has previously replaced some of the electrolytics and other caps in the past.
Both of the ones shown have a metal lug with one soldered to the chassis and the other soldered to a terminal strip. I don’t know the significance of this lug.
I haven’t read anything about these types of caps and hoping someone can advise me on how to properly replace these.
Attachments:June 28, 2021 at 4:29 pm #17007June 28, 2021 at 4:57 pm #17008Alistair ThomsonForum Participant
Dual caps are simply two caps in the same housing, normally sharing a terminal. In the case of 37 and 38 the two caps with the common terminal is clearly seen in the schematic. But that common is not ground! You should check that! In the case of 19 and 20 the common terminal is grounded.
In the early days they used common cans with multiple caps inside to save space and cost but nowadays single caps are tiny in comparison so there’s no need to do that. So all these dual caps can be replaced with single ones.June 29, 2021 at 7:42 am #17009
Thanks Alistair but bare with me. I’m still learning and these questions are probably basic. I’m getting better at reading schematics but I have a ways to go.
The schematic shows where 37 and 38 are but does not assign a value for each respective cap. Since it’s listed first on the parts list can I assume the 37 is the .008 and the 38 the .05. The schematic doesn’t indicate a value. Also the existing .008/.05 cap only has two wires coming from it, one to the tone control/switch, yellow circle on enclosed photo, and the other to a terminal strip. This same lug on the terminal strip also contains the + connection for two of the previously replaced 8 mfd electrolytic caps as well as a wire going to pin 3 of the 2A7 and from there going to the tone control/switch, blue circle on enclosed photo.
All this to say I am still confused as to how to wire in the 37 and 38 caps or how to check when you mention that the common is not ground.
Also does the metalband that circles the cap have any purpose? Is it there just to secure the caps?
I appreciate your patience.
Attachments:July 1, 2021 at 4:09 pm #17019Gary AlbachForum Participant
Hi Robert – you are correct that C37 is .008 uF and C38 is .05 uF. As Alistair pointed out, these two (2) capacitors are in the same cardboard tube. Two wires come out of the tube and there is a metal band circling the tube. One wire comes from one end of the .008 uF capacitor, and the other wire from one end of the .05 uF cap. The other ends of theses two capacitors are connected together and connected to the metal band.
To replace this dual cap you can use two individual modern poly caps, .01 uF (instead of .008 uF) and .05 uF. Connect the replacement .01 uF cap between the two lugs on the terminal strip that previously held one wire from the dual cap (the .008 uF section) and, on the other lug, the connection to the metal band.
The lug that was connected to the metal band also connects to pin 2 of the 2A5 (plate) and the output transformer.
The lug previously holding the .008 uF wire from the dual cap should also connect to pin 3 of the 2A5 (the screen grid) and the tone control.
For the .05 uF cap, (C38) connect one lead from the new replacement cap to the tone control, via the terminal strip (your yellow circle), and the other lead to the lug on the terminal strip that used to hold the metal band (but now also anchors one side of the new .01 uF cap). The other wire from the tone control returns to pin 3 of the 2A5 as before.
Replacing the other dual cap C19/C20 is easier. Again, the metal band is a shared connection for one end of each of the two caps inside the cardboard tube, and each of the wires emerging from the tube connects to the other end of each of the caps. Simply replace this dual cap with two individual 0.1 uF modern poly capacitors as shown in the schematic. One end of each of these caps is soldered to the chassis. (I had to search for these two caps on the schematic because they are drawn in very different places!)
For reference I have attached a couple photos of the construction of a dual cap.
Gary in VictoriaJuly 1, 2021 at 4:14 pm #17020Gary AlbachForum Participant
Here are the photos.
Attachments:July 1, 2021 at 6:29 pm #17023
Thanks Alistair and Gary for your help. Clears up my confusion. I can understand it now especially knowing the purpose of the metal band. I’ve seen metal bands before holding older large paper caps, but their sole purpose was to secure the cap.
I’m really enjoying attempting to resuscitate old radios, mostly meeting with success, mainly because of expert advice from this forum and other online information.
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