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American Bosch 5AC - Printable Version

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American Bosch 5AC - dseverson - 06-16-2015

[attachment=7466]Hello, all.

Just picked up this American Bosch 5AC (I think) and am getting ready to recap it and replace the resistors.  The schematic calls for twelve caps but I only see six under the chassis. I know that three are the filter caps (C19, C20, and C21), one is a mica, one is buried under the terminal strip, and one is a flat square labeled G.H. Longlife Condensor .006mfd.  I'm having a heck of a time trying to see where the other six are.

Here are links to the schematics as well as some photos.

https://app.box.com/s/l832e6urmwid8ponc5co

http://www.nostalgiaair.org/PagesByModel/566/M0029566.pdf

Dave

RE: American Bosch 5AC - dseverson - 06-16-2015

Here are the photos.  

           

RE: American Bosch 5AC - jerryhawthorne - 06-16-2015

dseverson some times they are well hidden! Have you explored the silver metal box shown on your third picture about dead center next to what I'm guessing is the output transformer? Many model radios stuffed low value caps in such cans.
Best, Jerry

RE: American Bosch 5AC - dseverson - 06-16-2015

I was wondering about that box right in the center. I'll take a look.

RE: American Bosch 5AC - Radioroslyn - 06-16-2015

Hi Dave
Should be easy to find. Note the parts list tell where the caps are connected. My bet is on the oval can next to the power xformer.
Note the power supply is drawn upsidedown. Bottom rail is B+. Top rail w/R-12 is B-

Terry

RE: American Bosch 5AC - jerryhawthorne - 06-16-2015

Dave, Terry is much smarter than me and indeed that oval can probably holds caps. My guess is the e-caps but there seems to be a label on it that might give you a hint. Unusual package size but who knows? Not me! Wire tracing to the schematic should help.
Best, Jerry

RE: American Bosch 5AC - Radioroslyn - 06-16-2015

Nah I just have a louder keyboard than most!!!


Terry

RE: American Bosch 5AC - dseverson - 06-16-2015

I am pretty sure that oval can does hold three caps - two 4mfd filter and a .08 field cap. The label on it is just a bunch of patent numbers and manufacturer info. It's completely filled with tar so it's staying as is. Just going to clip the wires and add in new caps under the chassis.

RE: American Bosch 5AC - jerryhawthorne - 06-16-2015

Your approach is certainly the easiest and will work well. I enjoy diving into the tar. It just keeps things look right underneath, but who will be looking? Tar is not that bad, a little heat gun after a large screw is driven into it and a yank. Well some times it doesn't work quite that well but you get the idea.
Best, Jerry

RE: American Bosch 5AC - dseverson - 06-16-2015

I know what you mean, Jerry. It's just a lot of tar. Might be able to pave part of my garage floor with all that tar. The metal box under the chassis is full of tar, too, and it appears that is where the rest of the caps are located. It's got ten wires coming out of it, so it holds five caps. I am pretty sure I can figure out which caps they are following the schematic. But now I am leaning toward attacking both the cylinder and this box with a heat gun to keep the chassis looking clean.

RE: American Bosch 5AC - dseverson - 06-17-2015

Correction. Looks like it holds nine caps with a common ground. Does that look right to you guys? I can't see where they are grounded, though.

RE: American Bosch 5AC - Arran - 06-17-2015

 Check the parts list page, it's pretty self explanatory what goes inside each block condenser can, it looks like it even gives the colour code for the leads. The filter condenser can has two capacitors inside according to the list, (in fact they may be large paper ones given the age of the set) since it has three leads, one goes to the transformer center tap, one goes to the filament connection on the rectifier, and the third goes to the B+ connection on the terminal strip. The bypass condenser assembly, no doubt the metal box under the chassis, dead center, has four capacitors, a 1 uf, a .01 uf, a .05 uf, and a .25 uf, so there are four wires, the ground end of each is likely soldered to the tin box which is screwed or riveted to the chassis, possibly with a blob of solder as well. One nice thing about this set is that if you want to break down and restuff the filter condenser can, the filter caps can easily be replaced with large poly film capacitors since they are only 4 uf each.
Regards
Arran

RE: American Bosch 5AC - dseverson - 06-18-2015

Just took the tar out of the bypass condenser. It definitely has 8 caps. Hopefully, I read the schematics correctly and have all the wires labeled for the correct caps. The wires have lost their colors. Next comes the filter condensor.

RE: American Bosch 5AC - dseverson - 07-04-2015

Happy Fourth, everyone.

Well, I replaced all the capacitors, including those in the oval can on top of the chassis and the metal box under it. I also replaced the resistors and a couple bad tubes. Problem is I am only getting a hum from the speaker that is not affected by the volume control. I don't get a hum when I touch the center post of the volume control. It does, however, measure close to 10k at full volume - what the schematics says it should be. I need to measure the tube voltages which are listed on the schematics but I don't know how to do it. Where do I attach either the positive or negative probe of my meter? Also, I measured the coils and I think they seem to be okay but could any of you give me the proper way to do it and possibly what the correct ohms should be?

Thanks again for all the help.

Dave

RE: American Bosch 5AC - Radioroslyn - 07-04-2015

Hi Dave & happy 4th!
Well there is a good reason why you don't get a buzz from the center tab on the volume control. It's not in the audio circuit but in the antenna circuit. It varies the volume by reducing the amount of RF that goes to the ant coil. If you want to hear a buzz go to pin3 of the 47 tube.
Most of the time you want the connect the - meter lead to the chassis and use the + lead to measure with. If you are using a VTVM or digital meter reading maybe a little higher.

Terry