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Author Topic: SB200 Standby Sw. Indicator LED  (Read 729 times)
SCUBA
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Posts: 74




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« on: October 18, 2008, 02:26:04 PM »

Hi,
A push-pull pot is on the way to allow the Rel Pwr Sens switch to function as a standby (blue wire, Harbach relay mod).  The push pull pot has extra contacts that I can use for a LED (or whatever) indicator (ie, 2 color LED to show standby or active status).  

Where, in the SB-200, can I tap a 5 to 12vdc power source to power up indicator LED?

Alternatively, if I should draw power from the meter lamp, what size/type diode(s) and resistor should I use?

I did a cursory search here, prior to posting this.

Thanks much,
Jack
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VR2AX
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Posts: 595




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« Reply #1 on: October 18, 2008, 07:48:09 PM »

The 3-500z tubes operate at 5V AC, so you could construct a simple half wave rectifier across the filament wires (not relative to ground). This should provide a DC volatage in the required range, provided the curent requirement is not too high (otherwise use a full wave rectifier).

VR2AX
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VR2AX
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Posts: 595




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« Reply #2 on: October 18, 2008, 07:51:01 PM »

I misread your post, the SB200 does not use 3-500z but rather 572b (6.3V filaments). Same procedure should however work. Apologies for the confusion, I must remember to put on my reading glasses.

VR2AX
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K0BG
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Posts: 9896


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« Reply #3 on: October 19, 2008, 06:39:40 AM »

Why would you want to bypass it, rather than turn is off?

The 572Bs are instant on (a second or two), and when I owned an SB200, I never worried about bypassing it. Ran 7 years until I traded it, on the original tubes yet.

Alan, KØBG
www.k0bg.com
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SCUBA
Member

Posts: 74




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« Reply #4 on: October 19, 2008, 12:20:17 PM »

Hi VR2AX,
Thanks, I have the parts on hand, and I can access that 6.3 volt right below the meter.

Hi Alan,
    I'm new to the SB-200; I did the Harbach mods, including the soft-start mod already.  Two Extra class hams strongly recommended install a standby switch (RCA jack going into the Harbach soft-key mod) to reduce stress on the tubes, etc, even though the Svetlana tubes are instant (or near instant) on.  

    I anticipate not using the linear all the time; by switching on if needed, or starting on and switching off.

    I'd like to take this opportunity to raise another question, if I may.  Using a peak reading watt meter, I am running about 550 to 750 output.  The book sez that I should show 2400 volts on the hi voltage, but I show only 1900 to 2000 volts.  Am I too low?

     I would speculate that it's the age of the amp that accounts or less than 2400v, and that the Harbach power supply upgrade and/or a full rebuild would bring it up to 2400.  Well, the bottom line is that the amp works great and brings in good compliments from distant stations.

Thanks much,
Jack
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KA5N
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Posts: 4380




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« Reply #5 on: October 19, 2008, 01:28:32 PM »

The high voltage is measured from a voltage divider consisting of three 4.7 meg 2 watt resistors in series with a small value resistor.  The 4.7 meg resistors change value with age and that will throw off the reading.  The Harbach power supply upgrade uses a string of 14 each 1 meg resistors in series (and other mods/parts).  Of course you can do like I did and use a piece of perf board to mount resistors on (and if you bother to calculate the correct series resistance is a bit less than 14 meg).  If the electrolytics are old that might also drop the voltage a bit.  I would recommend replacements.  Somewhere from 150 to 330 ufd 105 degree 450 volt units will do fine.
Allen
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K8KAS
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Posts: 570




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« Reply #6 on: October 29, 2008, 09:25:46 AM »

I have owned 3 or 4 different SB200 over a 35 year span and not one of them ever failed. Now I hear and read about all the Hardcrap junk and others selling this must have stuff for the SB200 and SB220 amps. They were trouble free for me for 35 years what has changed? Keep them stock and just use them. They were good designs to start with. Hams...Denny
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