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Author Topic: SEEKING INFO ON EARLY NCX-3 POWER SUPPLY? NOT REALLY BOAT ANCHOR BUT OLD  (Read 2409 times)
KM1H
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« Reply #15 on: September 20, 2018, 06:01:07 PM »


Any small 0-12 to 25V DC PS will be just fine. Use as a normal PS or reverse leads whenever you want a negative voltage.

Carl
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N6QWP
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« Reply #16 on: September 20, 2018, 08:13:13 PM »

Thanx Carl--For the gas tests, will I only need a variable positive bias voltage.....or will there by any need of any negative bias during that basic test?

I think I finally have all of the information that I need to set up the test platform.  Will be looking for some "safe" enclosure for the tubes and a variable supply for the bias while I am updating the AC-200 supply.

Looking forward to getting all this together and finding out the pre-story on all of the old tubes that I have collected.  Do not want to risk another blown up "good 30L-1".

After the preliminary test, I will get that old basketcase 30L-1 set up to run the tubes that pass, with some higher voltage and some RF.  I just found an original Collins transformer for it and have the parts to rebuild the old original power supply boards.

Hopefully, all of this effort and aggravation will yield some good solid 811A tubes that I will be able to use in my good 30L-1,

Couldn't have come this far with this project without all the great help from everyone who contributed their time and expertise.  Thanx all.....73



« Last Edit: September 20, 2018, 08:21:21 PM by N6QWP » Logged
N6QWP
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« Reply #17 on: September 21, 2018, 03:14:00 PM »

Well, managed to get two pieces of the project together today.  Plugged in the AC-200 using my variac but did not recap or replace the diodes=(was in too much of a hurry to find out if it would work or not).  After adjusting the AC to get exactly 12.6 vac for the filaments, here's what it puts out:
At 112 vac input:           NO popping, no smoke=ran for over a half hour.
                          12.6 vac @ 5 amps
                           900 vdc @ 300 ma
                           442 vdc @ 200 ma
                          -103 vdc @ 10 ma


I also managed to "fix" my HP 6824A variable ac/dc power suppy that had a bad switch.  

It will now deliver 0-80 volts at up to 1.2 amps.  That should deliver what I need for the bias in testing out the 811A tubes.

Now just need a caged chassis to install two sockets in for safely testing the tubes-two at a time.  

Making acceptable headway.
« Last Edit: September 21, 2018, 03:34:01 PM by N6QWP » Logged
N6QWP
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« Reply #18 on: September 21, 2018, 05:12:31 PM »

KE0EU...Mike, seems like your astute deducing the origins of this supply was pretty much right on target.  There are two chokes (one a later replacement) and while the voltages are a bit askew, (the HV B+ is low.....and the second lesser HV B+ is high), I now think that this is actually a NCX AC-500 supply that has been modified a bit....perhaps for another rig?  It is closer to that schematic.

The voltages that I get seem perfectly suited to use in the preliminary testing of my collection of old 811 and 811A and 572B tubes....according to Carl's suggestions (if I am correct in getting what he has been saying).

Thanx for getting me started on figuring out what I was starting with.  Made things a whole lot easier to get oriented and to comprehend what I was actually working with.

One thing that concerns me a little was that the bias voltage does not seem to have a bleeder resistor and it took about an hour for that -103 vdc to come back to 0.  The B+ voltages were very quick in doing so.

Don't know what this supply was last used for, but for my purposes it is perfect. Thanx again.

« Last Edit: September 21, 2018, 05:32:48 PM by N6QWP » Logged
KE0ZU
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« Reply #19 on: September 21, 2018, 08:42:51 PM »

Brad, the Bleeder for the bias supply is comprised of about 25K in the NCX-3 radio itself.  It is a series of 2 resistors and a 5K pot to adjust bias on the finals. You could just use a 27K 1 Watt resistor.
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Regards, Mike
https://mikeharrison.smugmug.com/
Pics and bold print are usually links.
N6QWP
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« Reply #20 on: September 22, 2018, 01:32:00 PM »

Thanx for that....will do.....eventually, along with caps and diodes.  

Do the voltages "seem right"?  They are higher than the A200....and the A-500 schematic seems very close.  Someone replaced one of the chokes.

Just trying to understand why the "lower B+" voltage was so much higher?  Not that it matters.  Could aging parts account for the differences?
« Last Edit: September 22, 2018, 01:36:53 PM by N6QWP » Logged
N6QWP
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« Reply #21 on: September 26, 2018, 07:58:32 AM »

Latest update:  Found a similar aluminum cabinet that is close to a good fit for the basketcase 30L-1.  Same basic design and colors.

Abandoning the idea of using the original transformer and power supply boards, in favor of just using the A-500 power supply for filament and B+....and the variable power supply for bias.

Using two of the tube sockets and disconnecting the output section, with the proper connections to sockets and plate caps,  I should have what is necessary to do the preliminary gas testing of those old 811, 811A and 572B tubes.

And it even looks close to "original"!  Now just have to figure out values for meter shunts for the old meter that I found.

Just wondering if the 300 ma @ 900 vdc of B+ that is available, is enough to test two tubes at a time....or if I should apply the B+ to them individually (getting the plates to glow by varying the bias voltage)?  They will be drawing current for some time during the testing....and "regettering".


« Last Edit: September 26, 2018, 08:11:18 AM by N6QWP » Logged
KM1H
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« Reply #22 on: September 26, 2018, 09:46:43 AM »

LMB Heeger used to sell a S Line size cabinet in their CO series, the CO-1 possibly.

As far as testing start with one and see what happens. The AC-500 is not a CCS supply but you can always use a pulser for two.

Carl
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N6QWP
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« Reply #23 on: September 26, 2018, 10:13:06 AM »

Thanx Carl--I'll test the tubes, one at a time.  Will take a bit more time, but safer and don't want to overstress the transformer.

If I understood your earlier replies, I'll want to increase the positive bias voltage until the plate starts to glow?  This will be for regettering the tubes after I let them cook for a while.

The one question I don't think was answered earlier, is does the position of the tube matter in regettering….or testing for gas???

I'll be using the old Collins 30L-1 which mounts the tubes horizontally.  I can of course, turn the amp testing platform so that the tubes are in a vertical position.....if that is better?
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KM1H
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« Reply #24 on: September 26, 2018, 12:49:38 PM »

If the tube doesnt arc over at HV application then go for the medium to bright red right away.....this is for 572's only. Orange is pushing it and yellow is BAD. Some fan cooling is good for long term regettering.

Getting 811 plates red only weakens the metal and changes its structure characteristics.You can try bringing up some plate current to barely color shows which is normal in ICAS SSB and then back down. That says the thing is at least conducting at DC, RF performance still unknown.

Vertical or horizontal with the large pins (filaments) vertical when tube is horizontal. The 30L1 is built that way as are all 811 and 572 amps back into the 50's. Early Chinese tubes had alignment all over the place and caused failures when the filament sagged into the grid.
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N6QWP
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« Reply #25 on: September 26, 2018, 03:45:50 PM »

Thanx for that clarification.  The 30L-1 deck still has the original fan, so I will make sure that it is hooked up.

Wasn't sure if the gettering material was affected by gravity.  I had read somewhere about swinging old tubes around in a sock to force the "mercury" (?) down to the bottom of the tube.

I have two tubes where the "coating" is spread up higher around the glass....thinner and further away from the getter.  It is no longer concentrated at the bottom.
« Last Edit: September 26, 2018, 03:52:06 PM by N6QWP » Logged
KM1H
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« Reply #26 on: September 26, 2018, 05:21:46 PM »

That coating was deposited by an old fashioned gettering process for sheetmetal anodes and once fired it cant be redone.

The shake the tube idea was used for mercury vapor tubes such as the 866A which can be as touchy as some hams on forums Roll Eyes Shocked I switched all mine to 3B28's and sold the 866A's at a fine price on Fleabay who like to stare at the purty glow. Kind of strange since most commercial gear has them in a cabinet where they cant be seen and were likely changed to the 3B28 or the plug in SS units many decades ago since they were a short life/high failure item.

Carl
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N6QWP
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« Reply #27 on: September 26, 2018, 06:32:29 PM »

OK....thought that might be erroneous information.  So, once the gettering coating has dissipated, there is nothing to be done.....horizontal or vertical mounting would not matter.  Got it!  

OK....last item on the list is a panel meter.  Figuring out the surplus meters that I have found, seems to be more than I can handle with the variable power supplies that I have (not graduated in easily read volts, closer than 5 volts).  Might be able to use a DMM for closer measurements?

Guess that I will have to "bust the bank" and try to find an original Collins meter for this old amp.  At least that way, the resistors and readings will already be correct.  Thanx and good evening.
« Last Edit: September 26, 2018, 06:41:23 PM by N6QWP » Logged
KM1H
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« Reply #28 on: September 27, 2018, 07:35:41 AM »

A $3 Harbor Freight DMM works fine...they are often on sale at that price and I have them scattered around in vehicles, garage, basement and every floor of the house.
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