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Author Topic: Swan 350 schematics question.  (Read 7116 times)
KK4CPH
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Posts: 154




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« on: October 29, 2011, 01:46:55 PM »

I have a question on the schematics on my Swan 350.  If I'm reading it right, after the jones plug, current goes thru the voltage regulator tube (OA2) first.  If that tube is bad, will nothing work?  When I turn on the unit, the power supply turns on but that's it.  Neither the S meter or VFO lights come on.  None of the tubes glow.  I can take the tube and have it tested but wondering if there's anything else I can check before making a 30 mile trip just to check the tube.  I have another power supply and the same thing happens.

Eric
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AC5UP
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« Reply #1 on: October 29, 2011, 02:00:02 PM »

Without looking at a schizmatic.............

Does the 0A2 tube light up purple when the power is turned on? Probably not, as what you describe is a total lack of power to the radio. The 0A2 is a shunt regulator meaning there will be a DC voltage greater that 150 vdc (but less than 185 vdc) in series with a power resistor in the ~ 1K range and the 0A2. The resistor limits the current to something the 0A2 can handle and there will be (almost) exactly 150 vdc across the regulator tube when it's operating correctly.

If the resistor is open there will be no voltage across the 0A2. If the 0A2 is bad (not too common) there will be no purple glow and the regulated 150 vdc line will read higher than normal. This has absolutely no connection to pilot lights or filaments as that's an AC circuit on a separate power transformer winding................
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KK4CPH
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« Reply #2 on: October 29, 2011, 02:51:33 PM »

Yes the tube lights up purple (took off the cover and looking at it from the side) 

Eric
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AD4U
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« Reply #3 on: October 29, 2011, 02:53:24 PM »

A bad OA2 will not cause the entire rig to not work.  The tube filaments should still light.  An OA2 regulates voltage around 105 volts at a few milli-amps.  Most of the tubes in the rig do not depend on the OA2.

Dick  AD4U
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KK4CPH
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« Reply #4 on: October 29, 2011, 06:48:08 PM »

Only the OA2 is lit up.  Is it possible the transformer has gone bad?

Eric
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AC5UP
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« Reply #5 on: October 29, 2011, 08:18:01 PM »

A transformer can go bad. To find out for sure if YOUR transformer has gone bad requires a schematic and voltmeter..................  Wink
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N2EY
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« Reply #6 on: October 30, 2011, 09:47:48 AM »

Only the OA2 is lit up.  Is it possible the transformer has gone bad?

Possible but not likely.

What's probably going on is that you have an open circuit in the heater circuit somewhere. Could be as simple as the power cable not being seated fully.

Do you have a voltmeter?

73 de Jim, N2EY
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KK4CPH
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« Reply #7 on: October 30, 2011, 12:56:53 PM »

Only the OA2 is lit up.  Is it possible the transformer has gone bad?

Possible but not likely.

What's probably going on is that you have an open circuit in the heater circuit somewhere. Could be as simple as the power cable not being seated fully.

Do you have a voltmeter?

73 de Jim, N2EY

Yes, I have a voltmeter.

Eric
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N2EY
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« Reply #8 on: October 30, 2011, 01:48:07 PM »

Yes, I have a voltmeter.

Then the first step is to determine why you don't have heater voltage.

How much experience do you have with tube gear? Do you have a manual and schematic for both the 350 and the power supply?

The first step is to determine if you have 12.6 volts AC leaving the power supply. This is measured first in the power supply itself, then in the rig. See the manual and schematics. Be SURE to observe proper safety precautions! Note that the 120 AC line voltage is sent through the power cord to the rig and back to the power supply so the power switch can be on the rig panel; there's voltage present on those wires even when the rig is turned off.

You probably have a bad connection, open wire, or other failure in the heater circuit somewhere. The power transformer has several windings and the B+ which makes the 0A2 glow is from a different winding than what powers the heaters. The 0A2 has no heater; it needs only B+.

73 de Jim, N2EY
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KK4CPH
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« Reply #9 on: October 30, 2011, 03:06:36 PM »

Jim
I have no experience with tube gear.  I have the schematics and a voltmeter/ohmmeter.  Looking at the schematics, it shows pin 4 is "12.6V to heaters" and pin 6 is ground.  I connected my voltmeter to those pins and it shows .72 volts.  So my power supply is toast?
Thanks for your help.

Eric
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N2EY
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« Reply #10 on: October 30, 2011, 03:56:48 PM »

Jim
I have no experience with tube gear.  I have the schematics and a voltmeter/ohmmeter.  Looking at the schematics, it shows pin 4 is "12.6V to heaters" and pin 6 is ground.  I connected my voltmeter to those pins and it shows .72 volts.  So my power supply is toast?

Maybe. More likely there's a bad connection or a short-circuit somewhere.

Here's how I would test it:

First, Unplug the power supply from the mains outlet and make sure all the filter caps are discharged.

Second, Unplug the rig-to-power-supply cable at the power supply.

Third, Put a jumper from Pin 1 to Pin 2 on the power suppy Jones socket. (Note: MAKE SURE you have the right pins!) This jups out the power switch, so the power supply will be ON as soon as you plug it in.

Fourth, Connect the voltmeter to read AC voltage from the heater secondary (12.6 volts). I'd do this inside the power supply, because a bad ground or connection could be the problem.

Fifth, Plug in the power supply. It should turn on and the meter should read 12.6 volts or a little more.

Sixth, unplug the power supply, make sure all power supply capacitors are discharged, and remove the voltmeter and temporary jumper.

It is highly unlikely that the power transformer is bad. You'd smell it, and it would probably blow the fuse in the power supply.

It is much more likely that there is a bad connection somewhere in the heater circuit. The transformer must supply 12.6 volts at 5.5 amps, and a bad solder joint, loose ground lug, loose contact or other problem could easily cause the problem.

Was the rig working, and then it failed? Or did you just get it? What's the history?

73 de Jim, N2EY



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KK4CPH
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Posts: 154




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« Reply #11 on: October 30, 2011, 04:14:20 PM »

Jim,
I bought this at the hamfest in Gray, TN 2 weeks ago in the tailgate section.  The guy said it turned on and that was it.  Both the PA tubes were missing so i bought them.  Other than that it was very dusty inside.  I don't know it's history.  For all I know I could have just bought a boat anchor.  I bought it because it was cheap ($50) and I figured I could learn something.  (Wanted to put all that stuff I studied for to pass the General and put it to use  Wink  )  It cleaned up nicely but if it's going to become a money pit, then I'll get rid of it.  I will do the test procedure you listed and see what I find.
Thanks again for your help!

Eric
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KK4CPH
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Posts: 154




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« Reply #12 on: October 30, 2011, 07:19:24 PM »

Jim,
It's alive!!!  Grin  I took the Jones plug apart and found a wire off and another one came off as I took it apart.  Not a whole lot of room in the plug to solder, but it turns on.  The S meter moves as I turn the VFO but the only problem is no sound!  No static... nothing.  I tried a different speaker and still nothing.  Here's what I'm not sure of:  On the front of the unit, someone drilled into the cabinet and put in a mini-jack. (1/8"?) and the wires run beneath the board. (would have to take it apart to see where it goes)  Maybe he decided to use headphones and bypassed the speaker.  Huh  I have no idea.  I'll have to do some digging around to see if I have a set of headphones with that size plug.  At least it turns on so I have hope! 
Thanks for pointing me in the right direction.

Eric
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KK4CPH
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Posts: 154




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« Reply #13 on: October 30, 2011, 07:31:43 PM »

OK, just hooked it up to my computer speaker. (1/8" plug) and it works!!  And it sounds terrific!  Cool
Don't know why I can't get sound out thru the Jones plug so he must have bypassed something.  But since the wires can be accessed inside the unit, I'll just run them out the back and into the factory speaker.  Now to find out how accurate the VFO is and see if it transmits.

Eric
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N2EY
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« Reply #14 on: October 31, 2011, 02:34:00 AM »

Just an open in the power cable.

Undocumented mods are the curse of used gear - you don't know what is changed and what is original.

Couple of things about the Swan:

1) Read The Fancy Manual - cover to cover. It is here if you don't have it:
http://bama.edebris.com/manuals/swan/

2) When you install the final tubes, be sure the plate caps are on properly. Otherwise you can ruin those new finals.

3) Do NOT try to transmit until you read and understand the tuneup procedure. Then practice tuning up into a dummy load first.

4) Do not expect high accuracy from the tuning dial. Particularly at band edges. Does it have a calibrator?

5) Remember this is a 1960s vintage rig and doesn't have the protective devices of modern stuff. Besides the usual high-voltage hazards, it is completely intolerant of operator error. Read The Fancy Manual!

73 de Jim, N2EY
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