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 Post subject: Silvertone 7171 Finished
PostPosted: Sep Tue 21, 2021 5:15 am 
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Joined: Sep Wed 19, 2012 3:34 am
Posts: 989
Location: Bethlehem, PA
This is one of those simple-yet-difficult projects. I got this one cheap about a year ago at Kutztown as part of a package deal and did not pay much for it.

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File comment: "Before"
Screen Shot 2021-09-20 at 11.24.32 PM.png
Screen Shot 2021-09-20 at 11.24.32 PM.png [ 528.87 KiB | Viewed 218 times ]


The electrical restoration took less than an hour. After replacing the capacitors it played, and there were only a handful of out of tolerance restores. The hardest part of the electrical restoration was a bad feedback problem causing a very loud squeal/howl. This I tracked down to the 6F5, and I tried subbing a 6F5-MG thinking a metal tube would solve the problem by having a built-in shield. But as it ends up, I could not get the set to play with any metal 6F5. There was no shield mounting/grounding bracket on the chassis to indicate there ever was a shield on this tube to begin with, so I used a goat style shield over the 6F5-G, drilled the top of the shield and bolted a jumper to the top of the shield which I then bolted to the chassis (I did not have a goat-style shield mount for the chassis and I reused a hole on the chassis for the chassis side of the grounding jumper so that the repair would be reversible down the line should a purist object to a shield being on that tube- this was before I knew how badly I was going to have to modify the set to make the mechanicals operate!).

Meanwhile, I stripped the cabinet by using a pocket knife to scrape of the original finish after photographing the toners used to make it easier to try to reproduce the coloring scheme.

Attachment:
File comment: Stripped
Screen Shot 2021-09-20 at 11.28.42 PM.png
Screen Shot 2021-09-20 at 11.28.42 PM.png [ 403.81 KiB | Viewed 218 times ]


I then used Aquacoat clear grain filler to fill the pores, hit it with a few coats of clear lacquer, let it set for a week and applied toner where indicated by the original finish.

Meanwhile, the mechanical aspect of the tuner became a nightmare I fought with for days (the thread on that saga is here).

Howard, who made the set for Silvertone, used a big plastic light diffuser disc to also control the tuning capacitor. The tuning knob freely spins on its own, with some pressed together fittings holding two big brass/copper washer-like fittings that "grab" the edge of the light diffuser disc. So when you turn the knob, it turns the disc using friction, and that disc is pressed into a pot metal part on the end of the tuning capacitor's rotor shaft.

The problem is, the light diffuser disc was in pieces and had been severely melted by the pilot lamps, which had also melted away the 12 o'clock position on the dial face. Someone had wanted to repair this in the past, but gave up when they could not take apart the pressed-together fittings, broke one of the tabs holding the dial glass on and broke part of the pot metal contraption that was seized onto the tuner's rotor shaft (I ended up having to cut it off).

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File comment: Diffuser disc
Screen Shot 2021-09-20 at 11.37.17 PM.png
Screen Shot 2021-09-20 at 11.37.17 PM.png [ 668.79 KiB | Viewed 218 times ]


After cutting and grinding apart the tuning mechanisms, I ended up having to make something new to work in its place and used a salvaged radio string pulley, glued together o-ring material, and some repurposed parts of the original assembly epoxied together with JB weld to come up with this contraption (below). The tuner's rotor shaft, interestingly enough, was tapped & threaded quite far (like, multiple inches) from the forward position, enabling me to use a small bolt to hold the dial needle to the rotor's shaft by simply screwing it on. I could not reuse the original dial needle screw because, in cutting off the pot metal mess on the end of the rotor's shaft, I had increased the gap between the rotor shaft and the dial face and now it wasn't long enough.

Attachment:
File comment: New tuning mechanism
Screen Shot 2021-09-20 at 11.39.24 PM.png
Screen Shot 2021-09-20 at 11.39.24 PM.png [ 856.62 KiB | Viewed 218 times ]


I was worried that the new dial face position would be recessed into the cabinet by about 1/4-inch but as it turns out, this was not the case. The tuning knob does protrude about 1/4" less out of the cabinet compared to the other two knob shafts (vol & bandswitch), but this did not end up being a problem for the knobs. Speaking of which, the set came with 3 mismatched knobs and I suspect only the middle one in my "after" picture (at the end of this post) is correct but I am not even sure of that. A few years ago I did a run of Chicago-independent repro knobs which I used to go on the left and right which look okay but well, obviously don't match. When I get back into making repro parts for myself I will try to replicate the middle knob for the left and right sides. My attempt at making my own knobs did produce functional results but I feel that 1- the surfaces just aren't smooth & shiny enough and 2- the resin is very easily stripped by the grub screws if I am not careful (its not as strong as real bakelite).

The tuning knob wobbles and has some play in it, but the set does function again and that's good enough for me. Sometimes it has a lag where it hangs up when starting to rotate the tuner, which can make fine tuning stations a little difficult. But at this point I really didn't have much to loose and I didn't want to give up on a set that worked fine.

Next I had to come up with a way of illuminating the dial, as the big pulley that now turns the tuning condenser takes up the space that originally would have been used by the pilot lamps.

I settled on using 1/8-inch thick light diffuser plexi to make this contraption:
Attachment:
File comment: New diffuser
Screen Shot 2021-09-20 at 11.48.56 PM.png
Screen Shot 2021-09-20 at 11.48.56 PM.png [ 1.1 MiB | Viewed 218 times ]


This plastic assembly simply slips over the tiny screw/bolt for the dial needle, and rests on top of the chassis. I had to extend the leads on the pilot lamp sockets (which now house LED pilot lamps so no more melting plastic). I flattened out the dial lamp brackets and drilled holes in them to bolt them to the new diffuser. I then used a high gloss metallic black to cover the forward facing parts of the diffuser that aren't behind the dial face, to try to minimize any light loss where it is unproductive.

The hardest part of this was getting the dial lamps as close to the dial as possible and getting the diffuser cut and shaped to fit below the board that holds the speaker. But this was not bad.

The new pilot lamp and diffuser arrangement works but not vibrantly. In normal room brightness, you can see the dial illuminate faintly. Under low or no light conditions the dial is easy to read. But if you don't watch the set come on, it is hard to tell that the dial is illuminated under normal room brightness or outdoor daylight conditions.

Radio now looks presentable and works, but it will never be as good as it should be. I will hold off on having RadioDaze make the dial until I know how long my repair will last. I do have a high res scan of the dial if anyone needs a Silvertone 7171 dial done by Radio Daze and don't have a good one to start from. Someone would need to use photoshop to repair the 12 o'clock burned spot and then having a new dial made will not be difficult. I'm just not sure my set after all these cobbled together repairs is worth the ~$35-40 it would take to have them do it.

The glaring flaw to my repair is that the dial is slightly positioned wrong, so the border of the left side of the dialface is obscured. But the JB Weld is holding so strong I can pick up the whole chassis by the dial face and don't want to cut it back off to try again.

Attachment:
File comment: Dial is off center
Screen Shot 2021-09-21 at 12.08.12 AM.png
Screen Shot 2021-09-21 at 12.08.12 AM.png [ 1.36 MiB | Viewed 218 times ]


But, the end result is pretty good considering the troubles encountered.

Attachment:
File comment: "After."
Screen Shot 2021-09-21 at 12.05.13 AM.png
Screen Shot 2021-09-21 at 12.05.13 AM.png [ 885.33 KiB | Viewed 218 times ]


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