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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Fri 20, 2020 2:13 am 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
Interesting experiment tonight - a 6J5 has the same basing as a 6C5, and is similar characteristics,
except a higher transconductance by a bit. So I substituted one of those in place of the stock osc.
tube.

The oscillator now runs on the high band, over about half (lower half) of the dial. So no wiring error,
something is possibly low Q as mentioned above, or the 6C5 I'm using (well, both of them that I tried)
is a bit of a dud.

At the upper range of its operation the oscillator can be more or less killed by touching the coil.


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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Mon 23, 2020 7:57 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
The top band can be aligned now, up to around 30 MHz. I think I will leave the 6J5 in there.

Is there any spec on how much signal is supposed to be on the grid of the 6L7 mixer? On the lower
bands it's very high.


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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Tue 24, 2020 8:58 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
Possibly it's time to re-wind the coil for that top band. It's phenolic right now, and that apparently has a pretty bad loss tangent. My go-to material would be teflon I suspect.


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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Wed 25, 2020 12:57 am 
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Joined: Jul Thu 12, 2007 9:44 pm
Posts: 87
Location: Zumbrota, MN
One of my favorites, I've done a couple of those. Great performers with unmatched audio into an adequte loudspeaker. Push pull 6l6s man! Here's a couple I've done


Attachments:
IMG_0156.jpg
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IMG_0065.jpg
IMG_0065.jpg [ 132.87 KiB | Viewed 455 times ]

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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Wed 25, 2020 2:28 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
Hmm. Those brass thumbscrews look oddly familiar.

Also - yours is missing the pointers on the knobs, like mine. Honestly I think that looks nicer that way.


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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Wed 25, 2020 3:33 pm 
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Posts: 87
Location: Zumbrota, MN
Was that you that turned those thumb screw for me Jim. It was 20yrs ago so? Yea those pointers get brittle and dont last sometimes.

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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Wed 25, 2020 5:16 pm 
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Joined: May Sun 22, 2011 11:27 pm
Posts: 361
Location: Dallas,TX
Brian your sets look great. You guys are inspiring me to dig mine out and get to work.

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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Wed 25, 2020 7:11 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
Yep, was me. Did I sent a print with those? Seems like, I need a few more now!


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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Wed 25, 2020 8:58 pm 
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Location: Zumbrota, MN
Right on, Thanks again. You can get them online and even ACE I found some once. Here's Home Depot. https://www.homedepot.com/p/Everbilt-10 ... /203537783

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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Mon 30, 2020 6:59 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
Band 5 oscillator: still not working correctly, apparently. So I removed the oscillator coil to see what's up.
Here's what it looks like:


Attachments:
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coil_2.JPG
coil_2.JPG [ 222.54 KiB | Viewed 390 times ]
coil_3.JPG
coil_3.JPG [ 326.82 KiB | Viewed 390 times ]
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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Mon 30, 2020 7:01 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
And here is what the space where it was, inside the set. The 100 pf capacitor indicated on the photo, is marked as 100pf
and is listed on the schematic as 100 pf. When measured it's really only 50 pF or a little less. So this needs to be replaced while
I am in there.


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100pf_1.JPG [ 231.54 KiB | Viewed 390 times ]
100pf_2.JPG
100pf_2.JPG [ 153.25 KiB | Viewed 390 times ]
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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Mon 30, 2020 7:03 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
In the meantime the main idea was to produce a similar coil using low loss materials. I chose teflon for the coil
form and for the wire insulation. First step was to draw what I needed to build.


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coil_dwg_2.JPG
coil_dwg_2.JPG [ 336 KiB | Viewed 390 times ]
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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Mon 30, 2020 7:05 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
Next was to fabricate the teflon form to match the phenolic original. Rather than make the copper right
angle brackets from scratch, I stole a few from the parts set I have on hand.


Attachments:
coil_form_new.JPG
coil_form_new.JPG [ 198.18 KiB | Viewed 390 times ]
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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Mon 30, 2020 7:07 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
The brackets in the original coil are held on with hollow brass rivets, which I could not source. So I manufactured them, out of brass rod.
This is a small instrument makers lathe that I use for parts like this.


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rivet_mfr.JPG [ 278.97 KiB | Viewed 390 times ]
lathe_rivet.JPG
lathe_rivet.JPG [ 244.62 KiB | Viewed 390 times ]
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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Nov Mon 30, 2020 7:10 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
It was a bit tricky to assemble it all but in the end it came out OK. The coil was then wound with solid wire as the original
was done, but using the same size teflon tubing as insulation as the original insulation, to keep the spacing correct. The
terminals were too complicated to copy so I used stake-in pins instead.


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assembled_form.JPG
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finished_coil_1.JPG
finished_coil_1.JPG [ 299.04 KiB | Viewed 390 times ]
finished_coil_2.JPG
finished_coil_2.JPG [ 357.69 KiB | Viewed 390 times ]
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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Dec Tue 01, 2020 1:36 am 
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Posts: 9804
Location: Beaver Falls, PA. USA
Mica capacitors are causing some problems now. I was just about to suggest checking them, but you beat me to it. On testing old micas, I have found some like yours, which were off value.

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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Dec Tue 01, 2020 2:00 pm 
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Joined: Jul Thu 12, 2007 9:44 pm
Posts: 87
Location: Zumbrota, MN
Good job.

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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Dec Tue 01, 2020 4:17 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
The top band (5) works now, over the entire range. Although putting a scope probe on the osc. grid will cause it to quit about
2/3 of the way up. The alignment is a bit dodgy but then it probably always was. I might try adding a some trim to bring it closer.

Paint for the cover is proceeding at all due speed!


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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Dec Tue 08, 2020 6:50 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
And "after" photos of the cover paint job. It's missing the brass thumbscrews at the moment, which are in the works:


Attachments:
painted_cover_1.JPG
painted_cover_1.JPG [ 336.46 KiB | Viewed 248 times ]
painted_cover_2.JPG
painted_cover_2.JPG [ 296.29 KiB | Viewed 248 times ]
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 Post subject: Re: Hallicrafters S-11 project
PostPosted: Dec Wed 09, 2020 3:31 am 
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Joined: May Sun 22, 2011 11:27 pm
Posts: 361
Location: Dallas,TX
Your black wrinkle looks great. Did you use a heat gun or oven?

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