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Author Topic: National NCX 3  (Read 13700 times)
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xe1yzy
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« on: April 28, 2010, 09:39:21 PM »

Guys,

I have a problem with the PTT circuit in my NCX3, my rig is an old version, and use a 6AN8 as a Relay control, all the schematics that I can found have a 6GH8 tube insted the 6AN8 (V7).

Does anybody have a copy of the schematics for the early NCX3 ?

Any help will be greatly appreciated!

Gracias!

XE1YZY
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Pete, WA2CWA
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« Reply #1 on: April 28, 2010, 11:12:41 PM »

Guys,

I have a problem with the PTT circuit in my NCX3, my rig is an old version, and use a 6AN8 as a Relay control, all the schematics that I can found have a 6GH8 tube insted the 6AN8 (V7).

Does anybody have a copy of the schematics for the early NCX3 ?

Any help will be greatly appreciated!

Gracias!

XE1YZY

Whether it's the V7 triode section of the 6AN8 or the V7 triode section of the 6GH8, just different pin numbers, all the connecting parts, resistors, capacitors, diode, etc. are the same and wired the same way. Trouble shooting the parts associated with the relay control can be used with either schematic as long as you remember the 6AN8 plate, pin 1, grid pin 2, cathode pin 3 and 6GH8 plate pin 1, grid pin 9, and cathode pin 8.
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« Reply #2 on: April 29, 2010, 10:25:25 AM »

Look at the schematic here http://bama.edebris.com/manuals/national/ncx3schem/


It shows the 6AN8.

Bill
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Bill KA8WTK
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« Reply #3 on: April 29, 2010, 10:56:42 AM »

If modifying be sure to go with a NOS 6GH8A.

Carl
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xe1yzy
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« Reply #4 on: April 29, 2010, 05:47:25 PM »

Many thanks to all...

Well, this relay must be energized when the rig is on RX, and for some reason I don't have enough voltage to close the relay, Im going to troubleshooting the circuit.

I let you know what I found!

Gracias!

XE1YZY
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WU2D
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CW is just a narrower version of AM


« Reply #5 on: April 29, 2010, 09:23:03 PM »

I had an NCX-3 in high school and college and used it mobile and even in my dorm room and had it in my first rental. I ran it on the heath mobile supply and the Heath AC Power supply and it did fine. I would say I owned one for about 10 years.

Hot Receiver and an excellent single conversion design. Good audio talk power too and it did not use up the sweep tubes - they lasted forever. But no RIT or CW offset and no CW sidetone, not that you would want to use CW since you would walk up the band with no offset! Mine did not drift.

Be careful of that relay circuit because it is a weakness of the radio. Like the brakes in my 65 Dodge Dart, the relay circuit needed pretty much a new tube every 10000 miles. That is a poor circuit at best. I even managed to burn up a relay when the tube must have shorted but was lucky and found another relay and put it in.

The triode is overloaded for that circuit in my opinion and it causes them to go soft in short order. This is a place where a mosfet would be a great thing to put in as the relay driver.

Can anybody think of a dual tube with the same footprint but a bigger triode?

Mike WU2D
 
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xe1yzy
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« Reply #6 on: April 30, 2010, 04:30:03 PM »

And the problem is...

  The relay are overloding the circuit, unfortunatly I don't have any relay like this in the junkbox  Sad
any recomendation about where to buy it please?

Regards

Pedro XE1YZY
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WU2D
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CW is just a narrower version of AM


« Reply #7 on: May 02, 2010, 04:25:14 PM »

The NCX-3 is backed by National's exclusive One Year Guarantee . . . your assurance of superb engineering and trouble-free operation... Hi.

Well I have to assume that you have removed the relay (A-50798) from its socket and have checked the 115 VDC coil and it is open.

Method 1 - Buy this http://www.onlinecomponents.com/buy/ALLIED-CONTROLS/TF154-6C-115VDC/


 Method 2 - Remove the coil - chuck it up on your cordless drill and attempt to rewind it with fine wire. Glue the coil back in place.

Method 3 - Replace it  with a 48V relay and a bigger tube and adjust the series resistor accordingly.

The physical layout is about 5/8 " wide and 1 1/4" long. one end has 1 pins ,labeled 1-2 and 3-4 these feed the coil. About 3/8" past the 2 pins is a small threaded stud,almost behind the 3-4 pins.the other end of the relay base has 18 pins{flat} in rows of 3,total of 6 rows. Other markings are on the coil DCL-725 and what looks like 9000 ohms. The ncx-5 also used the same relay.

Allied Controls made these in many voltages and quite a few hams will have something like them in their junk box - but most will be 48V or some other voltage like this:

http://www.swordfishingcentral.com/store/Relay-160421574532.html

http://www.maraindustrial.com/cart/electrical/relays/allied-control-tf154-cc-cc-48vdc-tf154cccc48vdc-relay-shelf-a33-ck.html

You can use a 24 or 48V relay but only if you want to wire in a mosfet switch and provide a separate power supply for it.

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xe1yzy
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« Reply #8 on: May 02, 2010, 10:49:58 PM »

The NCX-3 is backed by National's exclusive One Year Guarantee . . . your assurance of superb engineering and trouble-free operation... Hi.

Well I have to assume that you have removed the relay (A-50798) from its socket and have checked the 115 VDC coil and it is open.

Method 1 - Buy this http://www.onlinecomponents.com/buy/ALLIED-CONTROLS/TF154-6C-115VDC/



Hola Mike!

Well, can't complain about the National superb engineering HI HI, after all, this radio is almost 50 years old!,and  is a good looking Radio, isn't?.

Well my option with out a doubt is Method 1, and make some improvements to the circuit (Mosfet keyer), maybe I want to install a CW side tone too, and figured out what to do about the offset.

Someone at some point of the life of this rig, take away the relay base, and weld all the wires directly to the relay contacts, so I have to buy a new base too!, I guess Im going to make a complete restoration at once, ( change electrolitics, burned resistor, deep cleaning , etc.).

Many thanks for your help Mike, I would let you know about my progress!

Muchas gracias!

Pedro XE1YZY



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WU2D
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CW is just a narrower version of AM


« Reply #9 on: May 06, 2010, 07:05:37 PM »

Pedro,

The friends on the AM Forum are here to please! AM and boatanchors forever. 

¡Los amigos en el foro de la están aquí a por favor! La y el barco ancla por siempre a amigo.

Mike WU2D
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