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Author Topic: SWAN MARK 6B POWER SUPPLY  (Read 799 times)
WA4JQS
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« on: December 03, 2017, 03:03:36 PM »

My old swan 6 mts amp had been setting unused for 10 years along with my 3 drake l4b amps. at 71 I have decided I wanted to put the old tube gear back in use . make a long story short I rebuild the drake supplies new caps ect all work great. ordered the swan pm upgrade kit rebuild the supply hooked up the amp and nothing. THE  amp will not power up. took the supply back to the bench checked all my work could not find anything I have messed up hi hi... hooked back up still will not power up did smell something getting hot put the supply back on the bench found the 200 ohm resistor under the mercury relay was very warm. also there is a can 40mfd at 350volts across it. looks like it has leaked over time big  hunk   of white junk around the lead. going to get a new cap and replace it and the resistor next. my question is ? I think this pulls the mercury relay in. ?? does this relay have a delay because it is mercury or are the contacts just mercury wetted ? could this relay have gone bad setting ? if so is there a replacement  upgrade ?. thanks for any help
73 Tony WA4JQS
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N3QE
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« Reply #1 on: December 04, 2017, 03:24:13 AM »

I'm not an expert in the 6B - but the 40mfd 350V capacitor at the relay sounds just like the Mark 2 power supply step-start. You can see the Mark 2 step-start circuit here: http://www.cbtricks.com/Amp/swan/mark_ii/graphics/swan_mark_ii_power_supply_sch.jpg

In any event it's "just the step start circuit". The 200 ohm resistor and 40mfd capacitor form a time constant that result in the turn-on delay.

If you wanted to replace the mercury wetted relay, an appropriate modern part would be something like a HVAC relay or contactor. I think the coil voltage on the original relay must've been 40 to 120VDC or something, some modern AC relays will run fine off DC (They use diodes to rectify internally rather than a shading coil) but you'd have to test the appropriateness of the step-start circuit for any modern relay. It's likely you'd change that 200 ohm resistor so it has appropriate loaded pull-in and holding voltage for the modern relay.
« Last Edit: December 04, 2017, 03:26:39 AM by N3QE » Logged
W1QJ
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« Reply #2 on: December 04, 2017, 05:50:32 AM »

My old swan 6 mts amp had been setting unused for 10 years along with my 3 drake l4b amps. at 71 I have decided I wanted to put the old tube gear back in use . make a long story short I rebuild the drake supplies new caps ect all work great. ordered the swan pm upgrade kit rebuild the supply hooked up the amp and nothing. THE  amp will not power up. took the supply back to the bench checked all my work could not find anything I have messed up hi hi... hooked back up still will not power up did smell something getting hot put the supply back on the bench found the 200 ohm resistor under the mercury relay was very warm. also there is a can 40mfd at 350volts across it. looks like it has leaked over time big  hunk   of white junk around the lead. going to get a new cap and replace it and the resistor next. my question is ? I think this pulls the mercury relay in. ?? does this relay have a delay because it is mercury or are the contacts just mercury wetted ? could this relay have gone bad setting ? if so is there a replacement  upgrade ?. thanks for any help
73 Tony WA4JQS

Tony, My investigation into you question turned up some interesting information.  First off, let me tell you what I know after I looked into this for you.  Just by looking at the schematic we see that K2 is a "contactor relay" or just plain "contactor".   It is used in contactor fashion because s you can see in the schematic it controls the line voltage and current that turns the power supply on.  It actually has a demanding job in that it has to carry the full current  the power supply draws from the line.  On 120v it could be quite substantial but half that one 240v.

That said, investigation I did turned up two different types of K2.  I am assuming the early version of K2 was a typical open frame high power relay contactor with a value of 120v AC.  (117v in those days).  It was indeed a full AC relay.  If you had your power supply set for 120vac, you would put a jumper across  the 1.5K 20 watt resistor.   If you set up for 240v you would remove the jumper across the 1.5K 20 watt resistor and it would "chew up" the other 120vac that the relay did not need and still see it's 120vac it wanted to see.  I can assure you that the 1.5K resistor would get quite warm.  Moving on,

At some point in time probably the second version if the Mark II (there were 2 distinct versions of the Mark II) but that is another story.  Anyhow, Swan made a change to K2.  The difference  was that K2 was changed to a "Mercury wetted" type relay contactor.  I won't go into the explanation of what that is, but suffice to say it was an intended upgrade to K2.  I have worked on quite a few Mark II amps but I never had to deal with K2.  Most of what I had to do was to rebuild the power supply or do work on the RF deck or in most cases, convert them to 6 meters.  I actually own a Mark II at the moment but it is in storage. 

So like I say, K2 was later changed and the schematic shows a change in circuitry as well.  As you pointed out there is an electrolytic capacitor, a 200 ohm 5w resistor and a diode that shows up in the revised schematic.  The 1.5K ohm  20 w resistor is still shown in the later schematic as well, and you still have to change a jumper if you switch line voltage.  So what does this all mean?  Well I do not know for sure what the value of the new mercury relay is but looking at the schematic I can try to take an educated guess as to what it is.

The change in the schematic  with the additional 200 ohm 5 watt resistor and the diode and the 40mfd electrolytic capacitor tells me that the new mercury relay is probably a DC relay and NOT an AC relay like the older version.  Question is, what is the voltage?  Going back to the revised schematic  we still have either 120 or 240v heading to K2 like before, but now it hits a 200 ohm resistor.  That 200 ohm resistor will have a voltage drop across it based on the current through it.  Remember this 200 ohm resistor for a moment, we will come back to it.  Now we hit a diode, this diode will act as a rectifier and will rectifier the voltage passing through it.  It makes it pulsing DC where the peak voltage will be 1.414 of the AC value.  Then it either hits the 1.5K 20 watt resistor or it hits a jumper.  It then passes a parallel connected relay (K2) with a capacitor of 40mfd at 350v.  That cap will smooth out the AC ripple from the rectification of the diode and the relay will be looking at a fairly nice DC voltage.  My guess is that the 200 ohm 5 watt resistor drops the extra voltage that comes out of the rectifier so that the relay does not see a higher voltage than required. 

If you can take a look at the mercury relay, it should say on it what it's value is.  My bet is that it is rated somewhere between 110-117vdc.  So in either case I would suspect that the 200 ohm resistor would get warm and so would the 1.5K if the amp is on 240v. 

See if you can see a marking on that mercury relay. 
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W1QJ
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« Reply #3 on: December 04, 2017, 06:13:03 AM »

Tony, with all I said above, I don't know if that really answers your question.  But if that 40 mfd cap is puking its guts, it sure could be why the relay is not working.  I would change out that cap for sure if it is leaking.  Anything close to 40mfd would be fine.  I would also check the diode and see if it is ok and not shorted or open.  Make sure that if your PS is set for 120v that there is a jumper across the 1.5K 20 watt resistor and that if you have it set for 240v that the jumper across the resistor is removed.  Also check to make sure that the 200 ohm resistor is not open.  There isn't too much in that circuit.  The on/off switch just returns and completes the circuit of the AC loop.  Maybe the on/off switch is bad?  I doubt that if you were getting heat at the 200 ohm resistor so the switch seems OK.  Check the diode and resistors and replace the cap.  If you do that it should work, if not, maybe the coil opened up on the relay coil. 

I only hope that you did not have the amp set for 120v and then changed it to 240v and did not remove the jumper across the resistor.  That would burn out the relay coil in short order.
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N3QE
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« Reply #4 on: December 04, 2017, 06:42:58 AM »

Huh, I just relooked at the Swan Mark 2 schematic that has the 40mfd cap and the 200 ohm 5W resistor.

I had ASSUMED that was a classic RC time delay DC coil step start. But I'm wrong!

That relay isn't for step start, it's the HV transformer primary main power relay. Why put a time delay on that if it's not part of a step start? No wonder they went to mercury wetted contacts, they'd be welding the contacts in short order.
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W1QJ
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« Reply #5 on: December 04, 2017, 06:48:11 AM »

Huh, I just relooked at the Swan Mark 2 schematic that has the 40mfd cap and the 200 ohm 5W resistor.

I had ASSUMED that was a classic RC time delay DC coil step start. But I'm wrong!

That relay isn't for step start, it's the HV transformer primary main power relay. Why put a time delay on that if it's not part of a step start? No wonder they went to mercury wetted contacts, they'd be welding the contacts in short order.

Coreectomundo
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WA4JQS
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« Reply #6 on: December 04, 2017, 02:29:06 PM »

Thanks for the info it is wired for 220vac i do not recall ever putting a jumper across the resistor but will check. hope to get out to the shop tomorrow and go thru the parts cab's i should have some 40mfd 350v caps know i have a ton of orange drops i keep for restoring BA's . i do not recall the amp having a power up delay either but 10 yrs and at 71 years i could be wrong hihi... i have it on the bench in the ham shack work area and ill look at it again in the morning. i will also recheck the W8CQ rebuild kit to make sure i have not messed up when i build it.. thanks for the history on the Mark II Supply knew there were two relay types but did not know which was the latest. can see now why they went to the Mercury  contactor..
73 Tony WA4JQS
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WA4JQS
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« Reply #7 on: December 04, 2017, 03:12:24 PM »

update just ran by and checked only jumper is across B and C.. and its wired for 220vac.. the relay is 120vac coil .
 contacts rated at  20 amp 120vac  10 amp 220 vac. will replace the cap resistor and diode tomorrow..
73 Tony wa4jqs

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AA2UK
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« Reply #8 on: December 05, 2017, 02:09:32 PM »

Hopefully the relay and its associated circuits will fix the problem. On the off chance it doesn't carefully look at the multi-pin connector on the rear of the amplifier. I had another issue related to this connector. I re-seated and cleaned this connector and it
resolved the problem.
Bill, AA2UK
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WA4JQS
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Posts: 78




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« Reply #9 on: December 05, 2017, 02:51:28 PM »

gone thru my parts cab's did not realize i was about out of caps. found a 20 mfd at 450 volts and a 100 mfd at 500 volts.. going to have to order a few restocks and get some 40 mfd at 450 volt units while i am at it. Ill take the connector apart tonight and check it. hoping the cap replacement will fix the problem as was working when i pull off the desk a bunch of years  back.
thanks for the help
73 Tony WA4JQS
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WA4JQS
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« Reply #10 on: December 07, 2017, 04:10:53 PM »

ordered parts now to get them installed.
73 Tony WA4JQS
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W1QJ
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« Reply #11 on: December 08, 2017, 06:09:05 AM »

With a diode and that electrolytic cap I am pretty sure the relay is seeing DC voltage.  I guess the relay will respond to either.
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WA4JQS
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Posts: 78




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« Reply #12 on: December 08, 2017, 01:47:18 PM »

The relay in the Mark II and Mark 6B power supply is a
mini relay made by C.P.Clare & Co. of Chicago Ill it is
model MR-11  N.O. and the Coil is 120v 60 HZ.

73 Tony WA4JQS
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