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  #1  
Old 05-21-2009, 04:45 PM
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mashaffer mashaffer is offline
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Sparton rebuild

Geez, Seems like I have been posting here at AK forever and I just found this radio forum yesterday. Oh well, no one ever accused me of being observant.

I posted in another of the AK forums a while back about a few pieces that I picked up.

http://www.audiokarma.org/forums/sho...hlight=sparton

On of the neatest is the Sparton radio featured first in the above thread. It appears to be highly modified so it will be an interesting challenge. I just got an order of parts from radiodaze that should cover most of what I need so I intend to start on the project very soon. If there is any interest I will post occasional progress reports here.

mike
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Old 05-28-2009, 07:53 AM
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The Sparton is a nice mahogany console. Maybe a Danish oil treatment would hide most of those scratches. You could hit it with a light colored scratch pen first. Do keep us posted on your progress!
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Old 05-29-2009, 05:36 AM
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Thanks for the interest. Do you know any good sites where I could get a little history of Sparton gear?

I think this one has been heavily modified as the manual refers to the controls in terms of left and right as if front mounted and this one is on top and has no markings for the controls.

It has a very interesting and clever self inverting strategy which seems to take the signal impressed on the screen supply of one output tube to drive the grid of the second one.

mike
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Old 05-29-2009, 07:16 AM
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I don't know about it being modified, it would have been a lot of trouble, and for what? I did notice in the pics that the dial scale is a little out of square with the adjacent molding, but that could be sag in rubber mounts or whatever. It is odd there are no markings for the knobs. Most of these square sets had a door for the TT and a door for the radio, both on the front. So this is a bit unusual. Do you see any evidence of a former shelf or old mounting holes for the chassis? If not it is probably original.

I think I have a little Sparton history book marked on my other PC. I'll see if I can post a link.
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Old 05-29-2009, 09:07 AM
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Looks interesting!

Howard's Restore-A-Finish should get rid of most of those pesky scratches, I use it on all my old radios. I'd use The oak or walnut on those cases. Try oak first, if not dark enough, try walnut.

Welcome to the radio forum. I too, used to not be aware of it, so you're not alone..hehe

But I want to see those beauties cleaned up!!!
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Old 05-29-2009, 09:33 AM
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Here's some history of the Sparks-Withington (Sparton) company:

http://www.radiomuseum.org/dsp_herst...ompany_id=3407

And a writeup about a nice Sparton Equasonne 301, one of the icons of late 20s radio:

http://www.antiqueradios.org/gazette/sparton1.htm

They made some fabulous radios, including the 1936 Sparton Bluebird, which I would dearly love to have, but they go for crazy money.

http://www.antiqueradio.org/spar04.htm

Attached Images
File Type: jpg Sparton Bluebird.jpg (41.8 KB, 197 views)
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Old 05-29-2009, 10:10 AM
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There was an outfit named Xonex that made reproductions of the 1936 "Bluebird" here a few years back...IIRC, they were AM/FM sets w/cassette players, & I THINK, were tube sets...They went for ridiculous money, too, so I doubt if many were sold..The only thing about stuff like this is that they have the same problem as the 1959/60 Cadillac-the Height of Style & fashion RIGHT NOW, but in a few years, they tend to look almost insufferably silly.
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Old 05-29-2009, 11:03 AM
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Well, the repro with a cassette deck might look silly, but the original, never.
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Old 05-29-2009, 07:26 PM
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Thanks for the tips guys. The lacquer or whatever it is on this unit is quite thick. After using the wood restorer would there be some way to adequately fill in the missing clear coat or would one have to remove the old clear coat and reapply?

mike
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Old 05-29-2009, 11:37 PM
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Good question. I've never tried to do that. I know what you mean, but I don't know how to fix that.
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Old 07-14-2009, 11:03 PM
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Late this week I will finally get a chance to get started (slowly) on this taking the time to do it carefully. My plan is to Start at the output and work my way back. The PS caps will be replaced first. I intend to leave the can in there put but replacements under the chassis. There are only about a 1/2 dozen paper caps which I will replace with polyester. There is one 4uf electrolytic which I have a 4.7 to replace it with.

As I work my way toward the front end I will probably replace the CC resistors with MF and CF until I get to the rf/if sections. At that point I plan on leaving everything alone at first so as to avoid throwing the alignment off. If I end up needing an alignment anyway then I would probably replace those resistors too.

Does this seem like a reasonable approach? Also I imagine that I will spend a lot of time with the iron running but not in use. Since I don't have temp controlled soldering station should I put the iron on the variac and just run the voltage down a bit between uses to make it ready for quick heat up? What voltage would be a good starting point in that regard (30W iron)?

mike
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  #12  
Old 07-27-2009, 05:53 PM
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I got a copy of the Sams from Just Radios and I am glad I waited to get it as it clarifies alot of stuff. The picture on the front shows a different style radio than mine but there are a couple different models that this Sams covers so that is not too surprising. The chassis and controls look identical so I am quite sure that I have the right one.

I had assumed that the PS filter (which is CLCRC with field coil as L) would use the caps in 10-15-15 order. It turns out it is 15-10-15. It shows the rectifier as a 5Y3 but I am almost certain that it was a 5U4 that I pulled out of it. IIRC the 5Y3 has more voltage drop so I may need to procure one especially since the line voltage is higher these days. The 6F6 output tubes had been replaced with 6V6 however so will have to check the plate and screen voltage ratings as the 6V6 may be able to handle the higher voltage.

The document also has pretty detailed alignment procedure in case I end up needing it. It is interesting (I have never done an alignment) that the first step has the generator set at 456KC and the tuner tuned to 1600KC. In the procedure they specify a dummy antenna value. There are three different loads used; 0.1uf, 200pf and 400 ohms. I assume this means that you disconnect the antenna and replace it with the specified component. Is that right?

Interestingly no mention of the AVC in the alignment procedure but for the voltage map it states that AVC should be made inoperative (doesn't say how, I guess experienced tech knows how) and bias provided by 3V battery. I guess I need to trace out the circuit and figure out how to do that.

Another interesting fact is that all interstage trannies (coils) are fixed with a separate parallel variable cap. To this tyro this seems like a nice sturdy design.

mike
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  #13  
Old 07-27-2009, 06:18 PM
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If you posted a schematic or a link to a schematic there are circuit geeks hereabouts who would doubtless guide your efforts.
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Old 07-28-2009, 10:06 AM
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From what I've seen in old radios and TVs, sometimes a 5Y3 or other smaller rectifier is replaced with a 5U4 because that was on hand, but the 5U4 can draw more current for the filament, which may overload the transformer.
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  #15  
Old 07-28-2009, 03:26 PM
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Quote:
Originally Posted by toxcrusadr View Post
If you posted a schematic or a link to a schematic there are circuit geeks hereabouts who would doubtless guide your efforts.
Since this schematic is identical to the free one on the web I don't think there is any problem with posting it.



mike
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