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Central Electronics 10B




 
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Author Topic: Central Electronics 10B  (Read 4541 times)
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kb3ouk
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The Voice of Fulton County


« on: April 07, 2013, 06:09:22 PM »

On this transmitter, there is a single 3PDT relay, is it only for when you use VOX or should it work when you key the transmitter up manually? Had it turned on, the relay doesn't operate when I key it up (that's why I wanted to know if it was only for VOX) and after letting it sit turned on for a while the rectifier started arcing and smoke start rolling up through the chassis, looks like the power supply choke let go, it was warm to the touch and smelled horrible.
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WQ9E
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« Reply #1 on: April 07, 2013, 07:01:27 PM »

It may be too late for the choke but the problem is likely downstream from the choke, something is drawing too much current.  Have you made sure the proper size fuse is installed and checked/replaced filter capacitors?  If not do both and hope your choke survived.

The relay is activated when in transmit, either by VOX or manual control.

CE relays are known for having a high failure rate (open coil) with age.

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Rodger WQ9E
kb3ouk
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« Reply #2 on: April 07, 2013, 07:32:52 PM »

I figured that there was something wrong with the relay, so I'll have to see if I might have something suitable to replace it with,and I can't be too sure it the choke wasn't a replacement to begin with, it looks a lot newer than the rest of the parts. Same with the two modulation transformers, I'm almost certain they are replacements. Didn't have a chance to check the fuse, I can't get the stupid holder open, the cap is stuck somehow and won't twist off.
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WQ9E
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« Reply #3 on: April 07, 2013, 07:46:56 PM »

The first CE-20 I bought had a 20 amp fuse in the holder along with a shorted 6AG7, I am glad I checked.

The modulation transformers and relay both are prone to open windings from the very small gauge used.  I found that a pair of RS filament transformers made a fine substitute for the original modulation transformers.

You will find that it is easier to use a modern selectable sideband receiver with good filters to adjust the transmitter rather than a scope.  The pattern produced by a poorly adjusted phasing transmitter is difficult to interpret-especially if there is also some hum and poor carrier balance.  I use a spectrum analyzer which makes adjustment quite simple since you can view both sidebands and the carrier simultaneously but a scope (which is one of my favorite pieces of test gear) is the most difficult method to use and even more so if you are using a service grade instead of a lab grade scope.  If you are new to phasing type exciters it is very easy to misinterpret the scope pattern.
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Rodger WQ9E
kb3ouk
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« Reply #4 on: April 07, 2013, 08:42:41 PM »

I've found replacement coils for the relay, but $65 is a lot for one. The modulation transformers look ok, but they are not the originals, which I believe were potted, you can see the spots on the case where the circular cases were. Since for now I intend on using it for AM once I get it running, I'm not too concerned about the sideband suppression, but I think having the capability to be able to run LSB/USB with carrier might be handy on a crowded band, so I'll probably adjust that eventually.
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WQ9E
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« Reply #5 on: April 07, 2013, 09:17:00 PM »

If you aren't concerned about museum looks substitute a modern 110 VDC relay with a coil resistance of 10 to 12K.  You should be able to find one much cheaper than the $65 replacement coil.

With a modern receiver or transceiver you should be able to align you 10B in an hour.  If you don't have an audio oscillator use another receiver/transceiver in SSB mode with its calibrator on and the tuning offset to produce the desired audio tone. 

But make sure you have replaced all suspect caps before beginning alignment or you will end up chasing your tail.
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Rodger WQ9E
kb3ouk
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« Reply #6 on: April 07, 2013, 09:43:45 PM »

I might have a suitable relay, since functionality beats out museum looks with this one (chipped paint, rust spots, one knob has a piece missing). I'll probably just replace all the electrolytics in it.
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Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible
WD5JKO
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WD5JKO


« Reply #7 on: April 08, 2013, 06:40:16 AM »



Good reference on this little rig...
http://amfone.net/Amforum/index.php?topic=27305.0

Also my comments elsewhere apply.

Jim
WD5JKO
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kb3ouk
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The Voice of Fulton County


« Reply #8 on: April 08, 2013, 08:39:51 AM »

This one must be an early one since it doesn't have the plug on the back for an oscilloscope.
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Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible
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