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Author Topic: SUBSTITES FOR 30L-1 METER AND POWER TRANSFORMER AND POWER SWITCH?  (Read 4583 times)
N6QWP
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« Reply #45 on: September 12, 2018, 04:35:01 PM »

OK....that seems to agree with K5JXH's observations on his website....Just wanted some confirmation.  Thanx

ONE LAST QUESTION, regarding this project, concerns how you get the tubes to draw enough current to start to glow for testing for gas.

I was assuming that I would have to use the entire amplifier circuitry and load up a driven rf signal (from a keyed rig) and load the "test amp" into a dummy load.  Seems like a lot of stress on the driver rig to key it for long periods of time (over an hour?).

Your last reply about a variable bias power supply, seemed to infer that perhaps one could get the tubes to draw enough current by just adjusting that bias voltage (without using the entire amp and tank circuit)?

Are you able to get the "testing platform" (modified hf rf amp) to make the tubes draw enough current to cause the anodes to glow, so that "observable gas glows" can be seen and the tubes can be evaluated--WITHOUT USING THE OUTPUT CIRCUIT INTO A DUMMY LOAD (when driven by a rig)Huh

That would sure simplify the testing setup and procedure.

Once this is answered, I'll give us all a rest.  Many thanx for all of the great insightful information.
« Last Edit: September 12, 2018, 04:56:01 PM by N6QWP » Logged
KM1H
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« Reply #46 on: September 12, 2018, 05:35:39 PM »

What output circuit?  This is just a tube test jig and not an amp. I guess I wasnt clear enough in Post 29.

I use real amps for final testing and returning to the owners.

Quote
Once this is answered, I'll give us all a rest.  Many thanx for all of the great insightful information.

Promise? Grin Roll Eyes
Actually I enjoy doing this when there isnt some doofus sniping away Angry

Carl
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N6QWP
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« Reply #47 on: September 12, 2018, 06:14:24 PM »

Thanx Carl--I really enjoy "coming to school" and you are one of the best teachers that I have ever had.  I'm learning more here, than I could ever from ANY other source.

I guess that I am trying to use this old basketcase 30L-1 amp to accomplish BOTH TASKS.  I will install a heavy duty filament supply and use my variac to control how much HV I apply.

So....just to be sure that I get all this, by just varying the bias supply voltage, I can cause the tubes to draw enough current to cause the anode to start to glow....If I keep the HV below 1200 vdc, I can observe the "glows" to determine whether a tube is potentially going to flashover at higher voltage??

I guess I will have to "isolate the tank circuit with some kind of switch ) in/out....so that I can progress after doing the basic test and then proceed with the "loading it up test".

Is there anything else that I should know (Opps, I forgot to promise) when running an amp with an HF driver and into a dummy load, before I accept a tube as "good enough" to pass onto using it in my "good 30L-1"?

"By George, I think I've got it!"

« Last Edit: September 12, 2018, 06:36:24 PM by N6QWP » Logged
N6QWP
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« Reply #48 on: September 15, 2018, 07:25:42 PM »

 
      ********KM1H, CARL********

If you get a chance, could you please confirm that my understanding (as requested for comment, above) of the use of adjusting the bias is ALL that is needed to make the tubes draw enough current to test them for gas.

I just want to be sure that I actually have a good and correct understanding of what you were saying.

I just picked up a power supply at a ham swap meet today, for an old NCX-3.  Except for the correct filament voltage (will need another transformer for that), I think that I can use the power transformer from it along with a voltage doubler (original Collins 30L-1?) to run the tests on one 811A tube at a time.  I think it now delivers about 700 vdc at 200-300 ma.

I also picked up an adjustable power supply (0-50 vdc) that I hope I will be able to use for that bias voltage?

Thanx again, for helping me nurse along this project.  73
« Last Edit: September 15, 2018, 07:47:57 PM by N6QWP » Logged
KM1H
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« Reply #49 on: September 16, 2018, 08:54:24 AM »

Yes.

Back to a cranky lawn tractor and dishwasher
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N6QWP
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« Reply #50 on: September 16, 2018, 10:49:19 AM »

Great Carl--I guess I am finally ready to build up the supply to test the 811A's.

I just noticed that this supply (NCX-3 clone) ALSO has a -80vdc bias output on it.

That will only leave finding a 6.3vac  filament transformer.  If I put a pot inline with the bias voltage, I SHOULD be able to vary BOTH the HV (with the variac) and the bias for the initial gas testing.

Hopefully, here endeth the lesson......(for now ;-)  Vry 73's to all who contributed.
« Last Edit: September 16, 2018, 10:57:10 AM by N6QWP » Logged
N6QWP
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« Reply #51 on: September 16, 2018, 02:40:29 PM »

OK.....one mo' question (of course ;-)  

I notice that the NCX3 supply has a filament winding of 12.6vac @ 5amps.

Is there any viable way to reduce that voltage in half to 6.3, that will not affect the available current of that winding?

A single 811A needs 4 amps of current at 6.3 vac.  I am assuming that I will need another separate transformer for that...….but it would be much simpler (if some modification to the existing winding were possible) to use that 12.6 vac winding to supply the necessary 6.3 vac @ 4 amps.

I'd love to put two tubes in and wire the filaments in series.....but I fear that the current rating of that winding would not handle two tubes, each drawing 4 amps.

Anyone come up with an alternative solution?
« Last Edit: September 16, 2018, 02:57:34 PM by N6QWP » Logged
N6QWP
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« Reply #52 on: September 16, 2018, 06:08:37 PM »

Would adding another tube, WITH FILAMENTS WIRED "IN SERIES" ACTUALLY REDUCE THE VOLTAGE ON EACH TO 6.3 AND WOULD THE AMPS DRAWN "REDUCE OR DOUBLE.....OR REMAIN THE SAME"?= (THE POWER DRAW (AMPS) FROM THE TRANSFORMER)??

Would the 12.6 vac @ 5 amps winding be able to handle TWO 811A TUBES @ 6.3 VAC (4 amps each)Huh

Is this "THE SOLUTION"?
« Last Edit: September 16, 2018, 06:25:02 PM by N6QWP » Logged
G3RZP
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« Reply #53 on: September 17, 2018, 02:29:48 AM »

Two (or even 20!) tubes drawing 4 amps each wired in series will still draw only 4 amps. That's how the old tube TV receivers did it with a series heater string. This was common in Europe because getting rid of the mains transformer reduced cost considerably, and allowed the use on DC mains, and a half wave rectifier and big filter capacitors allowed the use of about 180 volts of B+ after filtering.

It had a downside, of course. The mains plugs in the UK 'standardised' as a fused plug with an internal fuse of between 1 and 13amps depending on application and defined live, neutral and earth pins. The power lead from the TV had, in those days, a red covered wire which went to the rectifier and a black, which went to the TV chassis. Red was always connected to the mains Live pin and black to the neutral: this meant that load on supply network had a lot of DC superimposed on it. When popular programmes were on TV and a break came leading to people switching on electric kettles, the extra load in addition to the DC was pushing the distribution transformers to saturation in many places, and they over heated and a number caught fire....usually on a Sunday night, when there were some very popular programmes.

The joys of 1950s and 60s Britain!
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N6QWP
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« Reply #54 on: September 17, 2018, 07:47:43 AM »

One further bit of explanation, please:  Two 811A's with the 6.3 vac filaments wired in series to a 12.6 vac @ 5 amp transformer will each get their required 6.3 volts.

The 5 amps "AVAILABLE" will then be SPLIT BETWEEN THE TWO TUBES? (providing ONLY 2.5 AMPS TO EACH TUBE)Huh   OR,

Will EACH TUBE BE ABLE TO DRAW THE REQUIRED 4 AMPS?Huh    If so, how?Huh

I'm having trouble seeing how the 5 amps (available) can still provide the TWO tubes with enough current (4 AMPS EACH) to heat up to the required temp.

This old brain keeps giving me visions of a 5 gallon bucket of water trying to fill two 4 gallon buckets.  Probably not a good analogy, but my thought process is hung up there.
« Last Edit: September 17, 2018, 07:54:09 AM by N6QWP » Logged
SM5GLC
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« Reply #55 on: September 17, 2018, 08:26:28 AM »

As the tubes are in series, they draw equal amount of current, i.e. 4A. Voltage is split in half over each tube. Just like two equal resistors in series.
No magic, just basic Ohm's law Cheesy If you have two items in series, the current always be the same, it cannot disappear magically, it is dependant on the sum of resistance. As the current is the same through the tubes, the voltage may vary (due to not perfectly matched filament resistance), and the filament power will vary accordingly.

And a 12V 5A transformer delivers 60W and having a 6V 4A transformer gives only 24W.
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N6QWP
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« Reply #56 on: September 17, 2018, 08:36:41 AM »

OK, thanx….

I guess I can see that happening, but I still have an issue of trying to get my mind to accept that a single 5 amp supply can deliver 4 amps to both of the tubes at the same time (without the transformer overheating or each filament getting less).  

I'll accept the premise based on Ohms Law....but I keep getting a vision of a water hose that is split into a Y.  When both are opened, the water flow is cut in half in each leg.  (I guess it is more representative of the voltage than the current).

This is great news, as I can temporarily use the same old power supply, pretty much the way it is.  Will replace the caps and use diodes, but the single transformer should provide what is necessary to run some preliminary gassing tests on those old 811A's.  

I'll still be looking for a separate filament transformer (6.3 volts at 4-5 amps) so that I can independently vary the HV with my variac.....to test one 811A tube at a time.
 
Tnx es 73 all
« Last Edit: September 17, 2018, 08:54:06 AM by N6QWP » Logged
N6QWP
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« Reply #57 on: September 17, 2018, 03:58:50 PM »

OK....."The Retard" is back.  Been pondering the above scenario all day and still having trouble making the case that each of the two tubes (when wired in series off of a 12.6 volt 5 amp transformer) is going to be able to get the FULL 4 AMPS OF CURRENT that each tube requires.

I get that the voltage will be halved....providing 6.3 volts to each tube.....AND I GET THAT while the current flow to both tubes might be 4 (or 5 if they are going to get the full measure of what the winding can supply).

Now that we have the correct voltage of 6.3 for each tube.....and that the maximum available current is 5 amps, why do  four 811A tubes "REQUIRE" 16 amps (4 amps each) of filament current when wired in parallel....and two tubes (each still requiring 4 amps INDIVIDUALLY) get away with achieving  their required FULL current from just a 5 amp source?Huh

I know that I am refusing to acknowledge something here, but if two tubes, no matter how they are accessing their REQUIRED CURRENT TO FULLY PERFORM, still require 4 amps each....4 amps plus 4 amps  equals 8 amps.  

I just can't get how one can get TWO tubes their FULL 4 amps each from a 5 amp transformer.  I CAN SEE HOW ONLY 5 AMPS IS AVAILABLE....BUT, it seems that they would have to split that available current AND RUN AT LESS THAN WHAT THEY REQUIRE?Huh?

Sorry to belabor the point so much.....I just wish somebody could get my stubborn brain into the correct "mode".  I'll give it up if nobody can clear this point up....but I sure would like to "get it" instead of just having to accept it ;-(
« Last Edit: September 17, 2018, 04:09:33 PM by N6QWP » Logged
W9IQ
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« Reply #58 on: September 17, 2018, 04:42:10 PM »

In a series circuit, the current through all devices is the same. When these are resistive devices like filaments, the current through the devices is the voltage of the supply divided by the total resistance of all of the filaments (I=E/R). Since a single filament needs draws 4 amps at 6.3 volts, its resistance is 1.575 ohms (I=E/R=6.3 volts/4 amps). Two of these in series (since resistances add when in series) is 3.15 ohms.

Now when you use a 12.6 volt transformer, the current is 4 amps (I=E/R=12.6 volts / 3.16 ohms). The short version of this is that if you double the supply voltage and place two of the filaments in series, the current through each is the same as a 6.3 volt supply and a single tube.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
N6QWP
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« Reply #59 on: September 17, 2018, 06:52:37 PM »

Thanx Glenn--I surrender!  Just confirm for me that the previous posting that stated that "2...OR even 20" would all get the required 4 amps from that same small filament winding was correct.
If that is, in fact true, I will accept defeat and go back to the books.   Tnx es 73
« Last Edit: September 17, 2018, 07:05:07 PM by N6QWP » Logged
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