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Author Topic: ASTRON RS-35A  (Read 282 times)
W3UZI
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« on: April 26, 2007, 07:10:52 AM »

I have acquired a used RS-35A P.S. the output of which is 13.5 volts, both resting and under load. The terminals on the back state "13.8 VDC". There seems to be no internal adjustment. Is this normal? Any advice welcomed!
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K5LXP
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« Reply #1 on: April 26, 2007, 07:16:21 AM »

I would consider that to be a "nominal" voltage, and entirely acceptable.  There is a tweaker inside if you care to make it exactly 13.8V, but for most practical purposes 13.5 is fine.

Mark K5LXP
Albuquerque, NM
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N4OGW
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« Reply #2 on: April 26, 2007, 07:17:30 AM »

There is a small trimpot inside that can be adjusted.

Tor
N4OGW
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W3UZI
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« Reply #3 on: April 26, 2007, 07:42:28 AM »

Thanks for your reply! I cannot see the trimpot, is it under the circuit board?
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W3UZI
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« Reply #4 on: April 26, 2007, 07:43:02 AM »

Thanks for your reply! I cannot see the trimpot, is it under the circuit board?
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K7PEH
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« Reply #5 on: April 26, 2007, 08:19:39 AM »

What kind of meter are you using to measure the voltage?  Given the natural error that such devices typically have plus the error that might be in your measurement, the current reading is probably just fine.

I just looked at my own RS-35M with the analog meters and noticed that parallax alone could easily produce a .5 volt error in reading.
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W3UZI
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« Reply #6 on: April 26, 2007, 08:26:13 AM »

Thanks.It is a Radio Shack digital self ranging multimeter #22-813 in current production.
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K5LXP
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« Reply #7 on: April 26, 2007, 08:41:13 AM »

Here's a link that should be of interest to you:

http://www.repeater-builder.com/astron/astron-index.html

Mark K5LXP
Albuquerque, NM

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W3UZI
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« Reply #8 on: April 26, 2007, 09:00:43 AM »

Mark, very many thanks for the link. I now have a gif of the circuit to study! At first glance there is no trimpot associated with the UA723. I remain happy with the 13.5 volts out.
Thanks to you and all the Elmers who have responded.
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AD4U
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« Reply #9 on: April 26, 2007, 10:21:28 AM »

The voltage trim pot is located on the bottom side of the PC board.  You have to unbolt the PC board from the top of the filter cap to get to it.  Since you are reading 13.5V on a Radio Shack meter, I would forget about messing with it.  Most Astrons are "right on" as shipped from the factory.
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K8AG
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« Reply #10 on: April 26, 2007, 10:56:09 AM »

Many years ago I had problems with digital meter accuracy.  They have the precision, but not the accuracy to back it up.  The one I was using would not even repeat well.

Also be aware that there is a .1 volt drop from no load to full load as well.  Difficult to regulate any tighter than that.

73, JP, K8AG
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N2CLB
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« Reply #11 on: April 27, 2007, 07:21:49 AM »

13.5V is fine don't worry with it
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