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Author Topic: Power supply grounding?  (Read 7291 times)
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KC2TAU
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« on: October 22, 2013, 07:45:14 PM »


This may be a simple question but I'd much rather ask it than possibly make a mistake and damage something. I have a power supply for my Hallicrafters ARR-7 but the B+ is about 70vdc too low. I have a Lambda 28M that will supply the correct B+ level but the connections confuse me.

The power supply that I am currently using with the radio is a fixed voltage power supply where as the Lambda is variable and regulated.

The fixed voltage power supply has a B+ terminal, A+ terminal and ground whereas the Lambda has both a B+ terminal, ground terminal, B- terminal as well as an A+ and A- terminal. The schematic for the fixed voltage power supply shows the ground terminal going to ground whereas the B- on the Lambda does not. Would it be unwise to connect from the ground of the fixed voltage power supply to the B- and the B+ lead coming from the radio to the B+ connection on the Lambda?
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flintstone mop
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« Reply #1 on: October 22, 2013, 08:07:20 PM »

Snooping around on the internet I see that 250VDC is needed for B+ and 6.3 V for the filaments. 12 volts for the tuning motor. There was a modification needed to for a certain tube. Our own W3JN knows about the re-radiation tube that needs to be bypassed.
Here's the link:   http://www.antiqueradios.com/forums/viewtopic.php?t=130093&view=next

Anyway it should not be too hard to get 250VDC into the radio. The P.S. you have now is not for the ARR 7? Anything will do.
Your power supply is only 180 vdc?
This ARR 7 is almost equivalent to an SX 28.
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Fred KC4MOP
KC2TAU
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« Reply #2 on: October 22, 2013, 08:45:13 PM »


At the moment I am looking to substitute in another power supply for the B+ just to see if the extra 70vdc will help performance. This is why I am asking about the grounding issue. I am simply asking whether or not it would be wise (and safe) to connect the B- of the Lambda supply to the grounded Ground terminal of the fixed voltage power supply. This is purely for testing but I would like to know if this is okay before I proceed.
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wa3dsp
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« Reply #3 on: October 22, 2013, 11:18:02 PM »

I think the Lambda supply has floating outputs.  You can connect either B+ or B- to ground or just leave it float. I would check that with an ohm meter or look at voltage from the B+ and B- to ground to make sure. If that is the case then you can probably safely series it with the other supply (I think that is what you are asking) to increase the voltage. I would think that it would have a supply to ground voltage limit of at least 250 volts. That might be in the specs.

The supply that does not have the isolated ground would have to be the first supply. Its B- is always grounded. Its B+ goes to the B- of the Lambda and the Lambda's B+ is the output.
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Patrick J. / KD5OEI
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« Reply #4 on: October 22, 2013, 11:24:40 PM »

good but in case it comes up later when voltages are higher, why not consult Lambda for the insulation ratings of that unit?
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N0WEK
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« Reply #5 on: October 23, 2013, 12:11:34 AM »

To me it sounds as if he just wants to hook up the Lamda supply to the radio to supply the 250 vdc to the radio.

In that case all that is necessary is to hook the ground and B- connections of the Lamda to the ground connection on the existing supply, which it sounds as if he's still using for the filament power, and wire the Lamda B+ directly into the B+ input to the radio. The B+ from the existing supply won't be being used at all. Connecting the Lamda floating B- lead AND the ground connection to the existing radios ground will give it a return path for the B+ and ground the case of the Lamda to the radio for safety.

Correct?
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KA2DZT
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« Reply #6 on: October 23, 2013, 12:27:46 AM »

On any of those regulated supplies you can ground either the positive or negative terminal.  In your case just connect the B- terminal to ground, same for the A- terminal.

Fred
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KC2TAU
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« Reply #7 on: October 23, 2013, 01:07:55 AM »

To me it sounds as if he just wants to hook up the Lamda supply to the radio to supply the 250 vdc to the radio.

In that case all that is necessary is to hook the ground and B- connections of the Lamda to the ground connection on the existing supply, which it sounds as if he's still using for the filament power, and wire the Lamda B+ directly into the B+ input to the radio. The B+ from the existing supply won't be being used at all. Connecting the Lamda floating B- lead AND the ground connection to the existing radios ground will give it a return path for the B+ and ground the case of the Lamda to the radio for safety.

Correct?

Yes, my existing supply doesn't supply as much B+ as I'd like and so I am subbing in the Lambda just for B+ and only temporarily just to see if the extra 70vdc will help performance any. I have an issue with a slightly insensitive S-meter and so perhaps the lack of B+ is affecting IF gain.
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flintstone mop
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« Reply #8 on: October 23, 2013, 06:25:20 AM »

I'm not trying to get nit pickin' but 250vdc is the B+ needed by the radio to operate.
And there was a tube in the set that needed some modification and it had to do with sensitivity. I included a link up from this post. John W3JN, here in amfone has knowledge about the "RE-Raditaion supressor"

http://www.antiqueradios.com/forums/viewtopic.php?f=5&t=130265
If you have lack of sensitivity; then it might be a defective I.F. can.
Fred
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Fred KC4MOP
MikeKE0ZUinkcmo
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« Reply #9 on: October 23, 2013, 09:50:29 AM »

Those old Lambda supplies are pretty nice.   Its a bit difficult to find them any more but they just worked year after year.   

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Mike KE0ZU

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KA2DZT
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« Reply #10 on: October 23, 2013, 11:21:31 PM »

Those old Lambda supplies are pretty nice.   Its a bit difficult to find them any more but they just worked year after year.   



I scrapped most all the Lambda supplies I had.  Too big and too heavy for what they do.

Fred
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