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Author Topic: HEATHKIT GC-1108 clock owners??  (Read 5502 times)
KD2E
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Posts: 231




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« on: December 03, 2011, 05:04:10 PM »

Anyone have this clock?  It is a bit more rare than the earlier ones.
I'd like to find out the procedure for changing from 24 hour time to 12 hour time.

Of course, its not a switch Huh
If it involves too much, I'll put it in the shack and use it as is. Sadly, I don't have the manual.

Thanks!
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KS2G
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Posts: 410




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« Reply #1 on: December 04, 2011, 12:05:15 PM »

Are you sure it's not a GC-1107?

(I can't find any reference to a GC-1108 online.)

The selection of 12/24 display in both the 1107 and the similar earlier GC-1005 is determined by the position of a single jumper during assembly.

You can find a schematic for the 1107 at:
http://www.vintage-radio.info/heathkit/

73,
Mel - KS2G
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KD2E
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Posts: 231




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« Reply #2 on: December 04, 2011, 02:41:25 PM »

I have both those two, but no...this is a GC-1108....with 9 volt battery backup.
It probably is a simple jumper or two, but not sure without the manual.
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N7NBB
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« Reply #3 on: December 04, 2011, 05:46:55 PM »

The wesite listed above
(http://www.vintage-radio.info/heathkit/)  offers a "FREE DOWNLOAD" of the schematic, and perhaps other info, it would certainly be worth a few seconds download to perhaps get "close enough" for your purposes.  You must have a RARE ONE !  I can hardly find any info, photos, etc on the GC-1108.
Hope you have good luck finding what you need.  My quest is about to begin in searching for parts for another Heathkit oldie - their IM-103 Line Voltage Monitor (meter)
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KD2E
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Posts: 231




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« Reply #4 on: December 05, 2011, 05:08:30 AM »

Thanks OM!!  But that website does not have the 1108   Embarrassed
By the way...I have an unbuilt IM103.
I also have a document which suggests which components to change....common failures.
I was thinking if I build it, swap out those components from the get-go with higher wattage.

.....Dave
« Last Edit: December 05, 2011, 05:10:44 AM by KD2E » Logged
N7NBB
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« Reply #5 on: December 05, 2011, 07:26:22 AM »

Sorry, in re-reading my post (above) I forgot to say the schematic WAS for the 1107 (not 1108) but I was hoping the schematic / board design would be close enough get you in the ball park as to which jumper might be the one you were looking for.
Thanks for the heads up on the IM103, yes I have the mods they suggest, and plan to implement them on my re-build.  Guess originally the components they chose to include in their kit were almost underrated to design tolerances, and the devices failed.  Still I really liked my meter hanging on the wall, if for nothing more than a conversation starter.
Wishing you best of luck in finding your information.
73
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W9GB
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« Reply #6 on: August 26, 2012, 06:23:52 AM »

Yes, I have the GC-1108 that I built as a kit around 1989.  I set up as a 24-hour display.
The unit is not rare, BUT it was one of the last clock kits that Heathkit offered from 1984 to ~1991.  
This model replaced the earlier GC-1107 (which used a fluorescent clock display).
The GC-1108 clock used Green LEDs for main clock display.

I will have to dig out the assembly manual, 12/24 hour conversion required wiring a couple of resistors and jumpers.
I will also have to check what clock IC chip Heath used in this model.
« Last Edit: August 26, 2012, 06:34:15 AM by W9GB » Logged
K4BNC
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Posts: 33




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« Reply #7 on: August 26, 2012, 02:44:26 PM »

Are you sure it's not a GC-1107?


The selection of 12/24 display in both the 1107 and the similar earlier GC-1005 is determined by the position of a single jumper during assembly.


73,
Mel - KS2G
I managed to find the old assembly manual for the 1107.  It shows the choice between 12 and 24 as involving both the positions of 4 jumpers and also adding 2 diodes for 24.
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KD2E
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« Reply #8 on: August 26, 2012, 07:43:11 PM »

Tnx w9gb!   Yup, that's the one....green LED. And does not use the wood grain plastic like the previous two.
If you find the info, could you email it to me at kd2e@comcast.net?
Tnx...Dave
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W9GB
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« Reply #9 on: August 27, 2012, 03:30:08 PM »

I have NOT found it, was not in my file cabinet.

Complete GC-1108 Assembly manual is on eBay right now.
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W9GB
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« Reply #10 on: November 23, 2012, 03:00:37 PM »

Quote from: KD2E
Anyone have the Heathkit GC-1108 clock?  It is a bit more rare than the earlier ones.
I'd like to find out the procedure for changing the displayed time from the 24 hour wiring to 12 hour wiring.
YES, I have the Heathkit GC-1108 clock.  This clock kit sold for $27.95 in 1990.
I found my Heathkit assembly manual over the holidays.

You MUST remove the 24-HOUR wiring (jumpers) before proceeding to the 12-HOUR wiring steps.
4 resistors and 2 diodes are required for 12-hour operation.
===
Pages 14 and 15 of GC-1108 Assembly Manual

NOTE: You can wire the alarm clock to display in a 12-hour or 24-hour format.
If you prefer the 12-hour format refer to the 12-Hour Wiring.  
Refer to 24-Hour Wiring, if you prefer a 24-hour display format.

Refer to PICTORIAL 2-2 for the following steps.

12-HOUR WIRING (Part A)
- R11: 1200 ohm resistor
- R14: 10 Kohm resistor
- D6: 1N4148 diode
- R4: 10 ohm resistor
- Install a 3/8" jumper wire at holes N and O.
- R10: 220 ohm resistor
- Install a 3/16" jumper wire at holes AA and AB. NOTE: You will have to reform this wire to fit the hole spacing.
- Install a 3/16" jumper wire at holes Y and Z.  NOTE: You will have to reform this wire to fit the hole spacing.
- D7: 1N4148 diode
- Solder the leads to the foil and cut off the excess lead lengths.
This completes the "12-Hour Wiring"

24-HOUR WIRING (Part B)
- Connect a 3/8" jumper wire at holes V and WW.
- Connect a 3/8" jumper wire at holes T and U.
- Connect a 3/8" jumper wire at holes R and S.
- Connect a 3/8" jumper wire at holes X and Z.  NOTE: You will have to reform this wire to fit the hole spacing.
- Solder the wires to the foil and cut off the excess wire lengths.
This completes the "24-Hour Wiring"
« Last Edit: November 23, 2012, 03:12:08 PM by W9GB » Logged
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