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 Post subject: Have never seen a cap like this
PostPosted: Jan Sun 27, 2019 6:26 pm 
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Joined: Feb Wed 15, 2017 11:49 pm
Posts: 221
Location: Kingsville, OH 44048
Hi all,
I bought this American Bosch 515 cabinet for $4 and figured I could find a cheap chassis for it. Well I did- it's an American Bosch 505. Everything seems to line up so far.
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I need a dial and pointer. We will see if they can be found online.
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The speaker needs some TLC too. It's bent a little and the cone is torn but VC and transformer ohm out good.
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But here's the interesting thing to me. I know most of you have seen these before but they are new to me. It's a dual .05mfd Micamold cap with the ground in the center attached to the chassis through the mounting bracket. Also just above that is a cheap generic cap with just a typed on sticker on it. There's a few of those throughout the chassis. Must have been a cheap way out.
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Anyway I just thought that was interesting HAVE A GOOD DAY!!

Dick


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 Post subject: Re: Have never seen a cap like this
PostPosted: Jan Sun 27, 2019 7:12 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 8510
Location: Beaver Falls, PA. USA
Oh, yes; Crosley and Belmont liked to use those double capacitors. It is easy for a "newbie" to mistake one for a single; I have seen it done.

Radio Daze might be able to make you a dial.

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Tim KA3JRT


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 Post subject: Re: Have never seen a cap like this
PostPosted: Jan Sun 27, 2019 7:47 pm 
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Joined: Sep Thu 14, 2006 3:27 pm
Posts: 11704
Location: Carmel, Indiana
Even if you did get a dial, how would you mount it? It looks like your chassis is missing the mounting assembly that attaches the dial on to the chassis.

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Michael Feldt
www.indianaradios.com


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 Post subject: Re: Have never seen a cap like this
PostPosted: Jan Sun 27, 2019 10:08 pm 
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Joined: Feb Wed 15, 2017 11:49 pm
Posts: 221
Location: Kingsville, OH 44048
Thanks Michael and Tim. I kind of thought there was something missing for the dial mount. Do you know of a picture of what it might look like? Maybe I could fabricate one. Thanks again

Dick Sowry


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 Post subject: Re: Have never seen a cap like this
PostPosted: Jan Sun 27, 2019 10:15 pm 
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Joined: Apr Sun 01, 2012 9:55 pm
Posts: 9877
Location: Seattle, WA
I like these radios, they have an attractive edge-lit dial.

The rear part of the assembly is there, which holds the dial lamp brackets.

There's also a front metal frame that the dial glass clips to, that masks off the edges of the dial. I'm sure such a thing could be fabricated, but it would take some effort.

EDIT: I'm wrong about the paperboard mask. I just went and looked closer with a flashlight. There's black paint on the back of the glass, and the rest of what I thought was masking is actually on the front of the dial pulley. It's a black disc to keep you from seeing the hub of the pulley through the dial glass.

Here are some photos of my Bosch 620, which uses very similar metal stampings.


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AmBo_620_chassis_frtop.jpg
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AmBo_620_dial_lit.jpg
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Rodney -- KG7EPW
Measure it with a micrometer, mark it with chalk, cut it with a chainsaw.
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 Post subject: Re: Have never seen a cap like this
PostPosted: Jan Sun 27, 2019 11:06 pm 
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Joined: Apr Sun 01, 2012 9:55 pm
Posts: 9877
Location: Seattle, WA
Here's a better picture.

I apologize, I'm rethinking this as I type. I'm going back to the mask theory. I've never actually disassembled my dial, so I'm describing what I can see from the front with a flashlight. I'm now thinking the dial glass is clear everywhere with no black paint on it.

You can see there are 4 concentric circular regions to one of these dials (numbered in green).

    1. This is the metal mask, in front of the dial glass.

    2. This part of the dial glass has a black mask behind it all the way to the edges of the glass. Likely paperboard or a metal sheet. Thin enough that I thought it was a layer of paint. I'm now thinking it's a mask, because you can see it's not quite aligned with the dial. It's not just the angle of the photo and the thickness of the glass; I confirmed with a flashlight that mine are slightly misaligned.

    3. This part of the dial glass lets you see the dial pulley through it. The pulley has the dial pointers attached.

    4. This part has a black disk behind it. The disk is attached to the pulley so you can't see the hub.

Hope that explains it.
Rodney


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AmBo_620_dial_detail.jpg
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 Post subject: Re: Have never seen a cap like this
PostPosted: Jan Sun 27, 2019 11:32 pm 
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Joined: Feb Wed 15, 2017 11:49 pm
Posts: 221
Location: Kingsville, OH 44048
Thank You very much Rodney. That's just what I needed to see. I know I can fab a bracket like that and then mount the dial on it with some kind of clips. I was just going to ask about the masking when I refreshed and saw your edit, so that's OK. If I have to paint the inside of the glass or maybe use picture frame matte it can all be under the clips holding the dial. Mine has been doctored before. In the cabinet there is a bunch of small nails and black masking on the inside around the dial hole. I just saw your PERFECT next post. Thank You very much. This pic is what's inside my cabinet. I doubt yours has this.
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Thanks again for all your effort on my behalf. But then again I suppose that's what this forum is all about This post is a perfect example of that.


Dick Sowry


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 Post subject: Re: Have never seen a cap like this
PostPosted: Jan Mon 28, 2019 4:06 am 
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Joined: Nov Tue 14, 2017 5:09 am
Posts: 1250
Location: Austin, Texas
Are you trying to get something like the original glass or just something that looks close to original?
If you will settle for something close, I suggest:
Copy the image above.
Use a photo editor to get rid of the pointer.
Print it the correct size.
Cut out the areas that say BROADCAST and SHORTWAVE.
Laminate the paper and mount it behind a piece of glass.

A pointer line on the black disk will show through the areas that are cut out.

Jay


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 Post subject: Re: Have never seen a cap like this
PostPosted: Jan Mon 28, 2019 5:48 am 
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Joined: Apr Sun 01, 2012 9:55 pm
Posts: 9877
Location: Seattle, WA
Dick, you're welcome. Glad to help. And no, I don't recall any tacks or black tape inside my cabinet.

Jay, not a bad idea, but there's a catch. From what I can find, the 515 (and the 505) are only 2 band radios, while my 620 is a 3-band radio. I think Dick would have a much easier time ginning up the graphics if he started with a photo of the right dial! :)

Also, not for a Bosch but for another radio, I've had Radio Daze create a repro edge-lit glass dial, and they did a very nice job. If you decide to go that route, note that the color layers (red and green on my dial) have a layer of white paint behind them.

-Rodney


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 Post subject: Re: Have never seen a cap like this
PostPosted: Jan Mon 28, 2019 7:06 am 
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Joined: Nov Tue 14, 2017 5:09 am
Posts: 1250
Location: Austin, Texas
I found this for the 515 but it needs a little work:
Attachment:
bosch-model-515.jpg
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Jay


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 Post subject: Re: Have never seen a cap like this
PostPosted: Jan Mon 28, 2019 7:47 pm 
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Joined: Feb Wed 15, 2017 11:49 pm
Posts: 221
Location: Kingsville, OH 44048
Thank you both for the help and replies.

So last night I was surfing and found on Ebay a 515 with a the bar missing across the grill and a few other blemishes. I offered the guy $30 and he took it. So I'm getting the correct chassis for my cabinet that is much better shape. I would have spent more than that on knobs for this thing let alone the dial if I couldn't make one.

This way I have 2 chassis and cabinets to make 1 good and correct radio.

I want to thank you guys for all the suggestions. That's what keeps us old guys kicking---making our minds work!!

Thanks again


Dick


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 Post subject: Re: Have never seen a cap like this
PostPosted: Jan Wed 30, 2019 6:53 am 
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Location: Seattle, WA
Congrats! Keep us posted on your progress, once you get the new unit!

-Rodney


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 Post subject: Re: Have never seen a cap like this
PostPosted: Feb Sun 03, 2019 3:45 am 
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Joined: Feb Wed 15, 2017 11:49 pm
Posts: 221
Location: Kingsville, OH 44048
Hi Guys

I received the 515 from Ebay in good shape but after checking it out this thing had major changes to it. The main thing being the speaker. It was replaced with a PM speaker but the output trans. was only 250 ohms so he added another trans in series (I'm guessing) to get the resistance up to what the original output trans. was--517 ohms. This actually boosted the resistance up to 663 ohms. I have an original speaker for this radio but it was stripped of its output transformer. I happen to have another output trans. when put in series with this small trans. would produce 530 ohms.
Would that be feasible or am I causing more heart ache for myself? The sec resistance is spot on for the Voice coil. I would just have to mount both trans. in a decent looking way. Maybe a baby Franenstien.
Also another question on the subject-- could you just add a resistor in series with the small output trans. to get the right resistance required? Thanks for any input

Dick

Dick


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 Post subject: Re: Have never seen a cap like this
PostPosted: Feb Sun 03, 2019 6:32 am 
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Joined: Nov Tue 14, 2017 5:09 am
Posts: 1250
Location: Austin, Texas
The DC resistance of the winding is not at all critical. What is important is the turns ratio between the primary and secondary. The specified load impedance for a type 42 tube is 7000 ohms. If you have a 3.2 ohm speaker, the impedance ratio is 7000/3.2 or about 2200 to 1. The turns ratio you need is then the square root of 2200 or about 47 to 1.

To check the transformers you have, apply about 10 volts AC to the primary winding and measure the AC voltage on the secondary winding. For a 47 to 1 transformer, the secondary voltage should be 0.21 volts with 10 volts on the primary. If you can't get exactly 10 volts on the primary, just measure both the primary and secondary voltages and divide the primary voltage by the secondary to get the turns ratio.

See if you can check the turns ratios on the output transformers you have available. If one seems to be in the ballpark, calculate the load impedance at the 42 plate by squaring the turns ratio and then multiplying by the speaker impedance. Older speakers are probably 3.2 ohms and more modern speakers will usually be 4 or 8 ohms. Something in the range of 5000 to 10000 ohms will work OK with the 42.

For speakers, the DC resistance and AC impedance are usually close to the same. A 3.2 ohm impedance speaker will usually measure about 4 ohms on an ohmmeter. The 4 and 8 ohm impedance speakers will measure an ohm or two higher on an ohmmeter.

Jay


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 Post subject: Re: Have never seen a cap like this
PostPosted: Feb Sun 03, 2019 8:01 pm 
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Joined: Feb Wed 15, 2017 11:49 pm
Posts: 221
Location: Kingsville, OH 44048
Thanks Jay After I wrote the post I saw another on speaker turns ratio and found a site that explained it pretty good. It was still a little confusing when you are just reading about it. Now at my bench with your instruction and the test equipment I see it much better.

I happen to have an output trans. that measures out to just under 6000 ohms so I think I'm in good shape there. Now I just have to mount it and see. Thanks for all the help.

Dick


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 Post subject: Re: Have never seen a cap like this
PostPosted: Feb Tue 12, 2019 4:24 am 
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Joined: Feb Wed 15, 2017 11:49 pm
Posts: 221
Location: Kingsville, OH 44048
Hi guys I know you missed the pain in your backside so here I am.
I'm still working on this American Bosch 515--replaced all caps and all but 2 resistors. Got the output transformer on the speaker. Had an open in the police band and got a donor from my 505 chassis. All other coils measured good. Here's the problem---I get 1 local station @ 102kc(supposed to be 97kc) and nothing else. To get that station good I need to grab hold of the antenna wire. I have a new 75' long wire antenna and when it's attached to this radio nothing but static. If I grab hold of the ant. wire it comes nice. By the way I do have the chassis grounded on copper water piping.
Even when I hold onto the ant. wire I still only get that 1 station.
I took some voltages: 80 Plate 302ac 302ac Fill 5
42 " 224dc Screen grid 230 control grid -16
75 " 143 " " " " -1.2
6D6 " 230 " " 83.8 " " 1.6
6F7 " 229 " " 83 " " 0.6 Anode grid if it's pin 4--121
if it's pin 5--2.2
http://www.nostalgiaair.org/pagesbymode ... 022317.pdf


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 Post subject: Re: Have never seen a cap like this
PostPosted: Feb Tue 12, 2019 4:33 am 
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Joined: Feb Wed 15, 2017 11:49 pm
Posts: 221
Location: Kingsville, OH 44048
Sorry about the last post. I'm not very tech savvy and I ran out of room and couldn't finish.
The recommended voltages are on the schematic if you can figure out the mess I made.

I just can't understand why I'm such a good antenna. Although I do know that lightning does like me.

Anyway thanks for any suggestions-- I really appreciate this forum.

Dick


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 Post subject: Re: Have never seen a cap like this
PostPosted: Feb Tue 12, 2019 4:35 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1164
Location: Cedar Rapids, Iowa, USA
On the left end of that Micamold cap, is that green covered wire protruding from the cap?


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 Post subject: Re: Have never seen a cap like this
PostPosted: Feb Tue 12, 2019 4:57 am 
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Joined: Feb Wed 15, 2017 11:49 pm
Posts: 221
Location: Kingsville, OH 44048
No That is actually the wire to the grid cap of the 75 tube tying to a terminal block. The wire goes thru a hole in the chassis to the grid cap.


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