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Author Topic: HELP!!! concerning a Drake 2-C receiver (circa 1965-68)  (Read 1307 times)
NN6EE
Member

Posts: 32




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« on: February 07, 2013, 01:03:01 PM »

Recently I purchased a 2-C sight-unseen and paid the price (not really working)  :-(((

In a nutshell what I did to TRY and resolve the problem was to replace ALL of the tubes (5) and 1 power audio transistor which made a slight improvement in audio out (but NOT MUCH!) The audio output is STILL relatively low and when I adjust it's (PRESELECTOR) when peaked for any one particular band it ONLY increases the signal barely!!!

Can anybody out here "POINT" us in the right direction to try and resolve this PROBLEM???

In advance a BIG "THANKS!!!",

Jim Davis-nn6ee
Concord, CA.
Ham since 1962 (but not versed in "Trouble-shooting!")
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K9YLI
Member

Posts: 859




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« Reply #1 on: February 07, 2013, 04:44:24 PM »

tube type equipment depends on  proper voltages through out.
first  thing would be to verify  all the  voltages being correct.

coupling capacitors also could be the probem.

touch you finger  the center pin of the  volumn control.
you should hear a thump inthe speaker. or a buzz.

you could feed audio  to the center pin from another source, see if  you can get
loud audio that way..
either an audio  amp problem  or  back in the  receiver  problem

seperate and substitute!!
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W4OP
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Posts: 408


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« Reply #2 on: February 07, 2013, 07:10:12 PM »

I have been restoring tube gear fro maybe 15 years or more. In all of that time, I have had one bad tube.
By shotgun replacing the tubes, you have pretty much guaranteed that an alignment is  now in order.
Get a schematic and follow the signal path backwards. One good place to start is the wiper of the audio gain pot.

GL,

Dale W4OP
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KA4POL
Member

Posts: 1965




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« Reply #3 on: February 08, 2013, 01:48:17 AM »

Usually capacitors suffer most from age.
There is a Drake Yahoo group where you'll find real expert information.
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KE3WD
Member

Posts: 5694




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« Reply #4 on: February 08, 2013, 07:00:13 AM »

So the "new" tubes didn't change the result. 

So put the old tubes right back in the holes, then find the Service Manual and Schematic for the beast and start troubleshooting. 

Voltage points from the schematic are a good starting place. 

Pencil to note any readings taken that greatly differ from what's on the schematic. 


73
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AD4U
Member

Posts: 2157




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« Reply #5 on: February 08, 2013, 08:16:19 AM »

I also restore old tube gear.  First since none of us can see the rig, we will assume that nobody has been "messing with or modifying" the basic design.  Since you have eliminated a bad tube being the problem, this is what I would do if it were mine

1.  Visually inspect each component for signs of over heating etc.  Resistors will buble or crack or look burned and SOME bad capacitors MAY start to bulge or leak out goo.

2.  Clean and then exercise all switches, pots, and tube sockets (remove tubes and then replace them and wiggle them while the tube socket is still wet) with DeOxit.

3.  Check all voltages at tube sockets against the voltage chart in the manual.  I would start at the power supply rectifier tube (6X4 or maybe the 2C uses silicon diodes) and go from there.  I have a set of tube "extenders" with numbered pins that enable one to check tube socket voltages on top of the chassis.  That make this process SO MUCH simpler.

I will bet this will bring the rig back to life at least a little.

4.  Perform a complete alignment per the manual.

5.  If the rig still is not up to specs, you will have to go stage to stage in typical trouble shooting manner until you find the problem.  "Bad" coupling capacitors usually will not cause improper DC voltage readings at test points.  They have to be located by trouble shooting stage to stage.

Good Luck

Dick  AD4U
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W0NTS
Member

Posts: 60




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« Reply #6 on: February 10, 2013, 12:12:09 AM »

I don't know if the 2-C is similar to a 2-B ( just a rehash of the S-B with slight circuit changes and different cosmetics), but the 2-B's were terrific receivers. I have had the pleasure of owning two. I know the 2-B had problems with the electrolytic caps in the power supply circuit and they need to be replaced by modern types. This may also apply to the 2-C. Since tubes appear not to be the problem with your 2-C I would suggest you clean all switches, pots and tube socket contacts. I recommend Caig De-Oxit for this. Many times dirty, corroded or oxidized contacts can cause problems such as you describe. If this doesn't bring back the audio, level use a signal generator to put a low level, modulated RF signal into the first RF amplifier (you can feed it into the antenna jack). From there use a signal tracer or oscilloscope and check each stage of the receiver. You should get progressively more signal gain with each stage, working toward the speaker. If you reach a tube/stage where it appears that the gain falls off, there is a very good chance you have isolated the problem to that area of the receiver. From that point start looking for a faulty capacitor i.e.: a coupling capacitor or a resistor that has changed value. There is a very good chance you will find your 2-C's problem using these procedures. Don't overlook the possibility the speaker may be the culprit. Try a substitute. LOL  Dennis Hoffman W0NTS
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