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 Post subject: PS design for vintage low frequency receiver
PostPosted: Oct Tue 12, 2021 3:34 pm 
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I have a vintage military receiver 15-600 kc, and I could use your thoughts on power supply design. I'd like to reduce the risk of introducing noise into the receiver.

The original AC supply for the (typo fixed) RBA-3/CFT-14654 receiver has a line filter ahead of the transformer primary. The PS is in a shielded enclosure, and has an "armored" cable - I assume to mitigate noise.

Faced with the unlikely reality that I may not find the CRV-20130 power supply & cable, I'm thinking of designing a replacement supply:
6.3 vac 3a
200 vdc 58 mA
105 vdc 1 mA

I would go solid-state, and I have some line filters from medical equipment I could employ.
Any other design considerations to avoid noise?
thanks!
Jeffrey

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Last edited by SmoothOscillator on Oct Wed 13, 2021 3:49 am, edited 1 time in total.

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 Post subject: Re: PS design for vintage low frequency receiver
PostPosted: Oct Tue 12, 2021 11:30 pm 
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Location: Burke, VA 22015
The RAB-3 is a HF version of the RAA. Its power unit is a CRV-20016.
Image
Image

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 Post subject: Re: PS design for vintage low frequency receiver
PostPosted: Oct Tue 12, 2021 11:58 pm 
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If you go with solid state, would you also include voltage regulation, using 3 terminal types, or even discrete?
Are VLF receivers more susceptible to noise? If so is that related to the frequencies within that band?
It's likely that the extra shielding you described was used because of the conditions that would be expected in a location where large numbers of receivers and transmitters were operated simultaneously
and possibly within close proximity of each other.
Long ago I had an RBC that was recently overhauled and properly aligned. I listened to the entire world on it.
Probably its best feature was that it would not have any part of any extraneous noise showing up in the output.

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 Post subject: Re: PS design for vintage low frequency receiver
PostPosted: Oct Wed 13, 2021 3:51 am 
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Quote:
The RAB-3 is a HF version of the RAA. Its power unit is a CRV-20016.


My fault: I have an RBA-3 - I corrected my typo above!

Quote:
It's likely that the extra shielding you described was used because of the conditions that would be expected in a location where large numbers of receivers and transmitters were operated simultaneously

That's right - I've seen pictures of those setups.

Yes VLF are prone to natural, and man-made noise.

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 Post subject: Re: PS design for vintage low frequency receiver
PostPosted: Oct Wed 13, 2021 1:48 pm 
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This is the power supply's schematic diagram, taken right out of the RBA instruction book, with the part values from the part list. Noted features are the custom wound line filter chokes and the tapped 10H filter chokes.

Edit:
Enough data was given to wind the line filter chokes. However since their inductances were not given, the filter's frequency response is also unknown. My educated guess is that in this instance the line filter should knock out everything above a few kHz that may interfere with the signals in the band 15 to 600 kc. For example, to cut off everything above 1 kHz with 125nF, we need 0.2H chokes (obviously smaller chokes for higher cut-off frequencies). So the medical line filters you have, which are mainly for EMI suppression, may not be sufficient.

There was a solid HV power supply design recently done by Jim in this thread:
https://www.antiqueradios.com/forums/viewtopic.php?f=12&t=399951&start=80
It could be adapted for your use if you want to eliminate the bulky and expensive 10H chokes. Instead of a HV linear regulator, smaller chokes with parallel capacitors could also be used to notch out the 120 Hz ripples (also discussed in that thread). A zener (or a strings of zeners) could be used in place of the voltage regulator tube since the current demand is very low.

Good luck with your project. That's a nice receiver to have.


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CRV-20130_Schematic.png
CRV-20130_Schematic.png [ 410.41 KiB | Viewed 322 times ]

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 Post subject: Re: PS design for vintage low frequency receiver
PostPosted: Oct Thu 14, 2021 3:41 am 
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Binh,
thank you.

Quote:
medical line filters you have, which are mainly for EMI suppression, may not be sufficient.

You're right; I've done a little more research on those.
I'm playing around with filter designs, I can glean an inductance from the coil descriptions using a single layer coil formula.
I'm not in a rush for this project, just research stages.
It's a very nice radio :)

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