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  #31  
Old 05-17-2010, 05:28 PM
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Ah,that makes sense... I was thinking up/down and not left/right. I don't know the tracking force of the dual, but it is probably somewhere around 1-2 g, and crystals are ~6-8g.

I'll end up seeing if it works just for the heck of it... if not off to ceramicville
Can one test the cart using a DMM (or AMM) set to mV, or is the signal too unsteady?

Edit: Pics posted. #s 46-58. (Reminder: Here)

Last edited by VintagePC; 05-18-2010 at 05:00 AM. Reason: Added pic info
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  #32  
Old 05-18-2010, 06:24 AM
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I think they test cartridges using a standard record with a steady tone, maybe 400 cps. Music would be all over the place. The best test is to hook one up and "see if it works."

From the pictures, the changer could use being taken apart and all the old grease and dirt cleaned out and white lithium grease and light oil used sparingly, keeping any oil off the rubber idler wheel. The wheel and every part it bears on can be cleaned with alcohol for better traction.
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  #33  
Old 05-18-2010, 06:51 AM
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Yep... working on that

I've already gone through the control tower and greased the sensing arm and linkages for the on-off switch. You can see a few shots (1042-1044) from when I started cleaning the control switch "plates"- they return to a light ivory white, and were nearly brown at first.

Someone did maintenance on it not too long ago. Many parts are still well-lubed and working smoothly (or the old grease hasn't dried out).

Next chance I get I'm going to pop off the motor and check that the bearings are still well oiled- if so, then I should be able to hook it up to something and get a signal (well, if the cart is still good). I also need to lube the speed selector mechanism; it feels a little chunky. The table itself glides smoothly, and I Li-greased up the changer gear under it to keep it quiet.
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  #34  
Old 05-18-2010, 11:56 AM
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Cartridge info?

Does someone have _definite_ specs on the cartridge? It is a TC8S, with (as mentioned, TC8G and TC8RS styli). Some sites say stereo, some say TC8 was mono, etc. etc...

It seems to be wired for stereo, with one of the three pickup wires being a common ground (bridged at the terminal block under the turntable), with the other two going to the center pin of the phono plugs. Yet another site suggests that there was one wire for each needle... Very confusing.

Also: there's an adjustment screw at the top of the changer tower, under the tone arm (in the block that holds it to the shaft). What is this screw for (visible in lower left of image 1039- perhaps auto-return trip point adjustment)? I _will_ need to remove that spring assembly from the shaft at some point, how critical is it to get that back to that exact position?

With regards to the rest of the set: Once I finish the turntable, I'm going to re-stuff the electrolytic multi-cap. do I still need to do the others, because they seem to be plastic/metal sealed (and not wax/paper). There's a better chassis shot in the last bunch of photos.

I'll also be checking the resistors and replacing any that are out of spec so I can get them in with my order of caps.

Sorry for all the questions I'm not experienced in this area at all, but I'm fascinated by this stuff and can't learn enough- there's something awe-inspiring about watching the intricacies of such mechanisms at work.
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  #35  
Old 05-18-2010, 03:08 PM
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What kind of audio wiring do you find in the changer assembly? There should be
two shielded cables with a common ground, with the inner conductors connected
to the each of the live terminals (Left and Right) of the cartridge. The third
terminal on the cartridge should be connected to the common ground (shield) of
the cables.

Regarding capacitor replacements, at least the three interstage capacitors
should be replaced. If they are leaky at all, they will allow a positive bias
on the first grids of the 6AU6 or 6AQ5 tubes, which may kill them and other
components in short order. Those capacitors are C10, C14 and C19.
The DC voltage on the grids of these tubes (pin 1 for the 6AU6 and pin
7 for the 6AQ5) should be zero at all times, as they are connected to the
ground through the potentiometers and no grid current is normally flowing.
If you choose to go with the existing capacitors, at least do hook up a
DC voltmeter and check each of these voltages. Also, do not operate
the amplifier without a load connected to the speaker outputs. A 2 watt,
8 or 10 ohm resistor connected between the 8 ohm tap and ground of each
transformer would be fine if you don't want to hook up the speakers.
Good luck!

P.S.: Another tip - do not do any restoration work yet (except replacing big
capacitors such as C5/C6/C7 if you wish) in the tuner area, it is too easy
to disturb things there.
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  #36  
Old 05-18-2010, 05:02 PM
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Hmmmm... the wiring is indeed as you describe (sorry if I wasn't clear).

- I took undergrad physics, so let's see if I learned anything:
The load is needed so that the back-EMF from an open transformer doesn't fry the output tubes, right? (and I should check those for opens/shorts too)

Thanks for the info on the caps. I'll have to look and see what I have in my parts bin; if I have to order, then I may as well get them all to get the most out of the shipping costs.

Slow going for a bit (some other stuff on the go) but I'll start a detailed HTML page soon.

VintagePC
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  #37  
Old 05-19-2010, 05:29 AM
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Good place for caps, in case you don't know, is Just Radios, Canadian, very helpful folks.

http://www.justradios.com/
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  #38  
Old 05-19-2010, 10:46 AM
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My preferred source is DigiKey (excellent customer service) but they've recently changed their shipping setup on the web site... so if I have to pay $20 for shipping (used to be flat-rate $8.00 except for oversize/heavy), I'll definitely go with JR.
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  #39  
Old 05-19-2010, 11:10 AM
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Quote:
Originally Posted by VintagePC View Post
My preferred source is DigiKey (excellent customer service) but they've recently changed their shipping setup on the web site... so if I have to pay $20 for shipping (used to be flat-rate $8.00 except for oversize/heavy), I'll definitely go with JR.
Digi-Key is fine for the latest SMT components and the like, but for
the kind of parts used in old radios, a supplier like justradios is
definitely recommended. I have bought a general purpose kit
of capacitors from them and was fully satisfied. Also, do a web
search with the keywords hamfest and the name of the nearest
large city. A hamfest is a kind of flea market organized by and
for amateur radio operators (hams), and all kinds of goodies related
to the old radio hobby can be found there. But maybe you already
know that from your old computer hobby...

Bye for now!
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  #40  
Old 05-21-2010, 06:29 PM
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Good news: I repaired the dial string and it looks to work: I cut some strong cotton thread to the same length as the original, coated it in candle wax, and strung it up. The tuning knob now works, so all I'll need to do is give the needle a nudge if it is in the wrong spot.

Here's where things get difficult: I've noticed some differences between my set and the schematic, such as cap and resistor values. Perhaps it is based off the 2053 but with some revisions?

There's also some bad news- one side of the coil marked L2 appears to be frayed. any suggestions as to what I can do?

Thanks,
VintagePC
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  #41  
Old 05-21-2010, 10:08 PM
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Can you post a clear close-up of the coil? I just ran into such a situation. The fix depends on how the coil is made. If you can check continuity with your ohmmeter it may be OK, though.

Sending you a PM.
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  #42  
Old 05-23-2010, 06:36 PM
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Ok... quick updates:

- I have snaps of the coil, but they'll have to wait until Tuesday; large photos aren't dial-up friendly

- I've been de-rusting the chassis... a couple of spots that I want to take care of before they get bigger.

- First tests of the LP deck: motor works and runs smoothly. A bit of a hiccup with the auto- shutoff not catching, but some Li-grease and a spring adjustment later, and all is well. Can't test cartridge yet, as the tone-arm hinge was broken. The epoxy is now curing. There's not much stress at that point, so it should hold.

- Working on a restore log... watch for it soon
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  #43  
Old 05-25-2010, 05:24 AM
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Okay... two birds with one stone.
Here's the build log so far. There is a picture of the frayed coil as the last item on the page; you can click any of the images for a larger version.

Enjoy!

http://vintagepc.co.nr/site/index.php/stuff/radio/

Also, feel free to leave comments as to what you think of the site's layout/design. I've put some time in to revamping it and I'm happy with the result- simple, clean and elegant.
Hope you like it too!

Last edited by VintagePC; 05-25-2010 at 06:46 AM.
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  #44  
Old 05-25-2010, 08:07 AM
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I like your website with the built-in links and all. That coil got lunched, didn't it? Hard to tell but if it was just the outer wires, I'd make a careful drawing of the orientation of the coil in the set and where all the wires go, unsolder it, take it out, and try to scope which broken wires go with which ones. But this coil "looks" like it's beyond that.

One thing you could try, then, would be to carefully unwind the broken turns of the coil, keeping the wire, until you get to just one wire coming out of the good part of the coil. Then carefully scrape to bright copper and solder that wire to the broken pieces one after the other and wind back on as neatly as possible. It's important to wind in the same direction as the coil was originally wound. You won't be able to wind like the machine but that's OK. Have a candle going nearby and drip wax on the coil as required to keep it together. Reassemble and it might work. It might require the tuning cap trimmers readjusted to get it to track.

Another fix would be an oscillator coil out of a junked plastic table radio. Someone on the forum might have a junker that he could send you the coil from: I don't have one at present or I would.

If not, AES sells replacement oscillator coils. I don't know which of these would work in your set, but they're cheap and one of them would: I'd get both and tack them in and try them. Search "oscillator coil:" see the first two $1.95 coils on the page.

http://www.tubesandmore.com/
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  #45  
Old 05-25-2010, 08:54 AM
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Quote:
Originally Posted by Reece View Post
I like your website with the built-in links and all. That coil got lunched, didn't it? Hard to tell but if it was just the outer wires, I'd make a careful drawing of the orientation of the coil in the set and where all the wires go, unsolder it, take it out, and try to scope which broken wires go with which ones. But this coil "looks" like it's beyond that.
Thanks- glad you like it!
I wonder if it was the mice, or whether it was something else; there aren't any bite marks in the wax, so it looks more like careless handling or a scrape against a sharp edge.

I'll give the repair a try and see what happens. I think it looks worse than it is because of all the fluff that is present. If not, I may have a spare coil from a junked stereo set I can use- I've amassed quite the pile of spares over a few years; all manner of toroids, transformers, and so forth. We'll see what happens- Thanks for the link to AES.

There are two coils on the same core there... I take it one is for the oscillator, and the other is a "hum-bucking" coil?

Regarding the trimmer adjustment, what would that entail? I don't have extensive sophisticated tools on hand.
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