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Author Topic: replacing an old relay  (Read 275 times)
NR5P
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Posts: 131




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« on: November 02, 2008, 09:37:07 PM »

Hi I have an hp 608 signal generator and it has a relay that actuates for 3 volts output which is not opperating or drawing the 5 ma through the coil like it should for some reason, I guess an open in the coil somehow.  It's a potter and brumfield rs1124 relay and should be 5ma coil current at 300 volts.  Is there anywhere I can find a replacement that would be a solder in?  I want to keep it as original as I can.  I guess maybe the only option would be to rewind the coil which would be a project I imagine in itself.  Thanks, Nathan
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N5LRZ
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« Reply #1 on: November 03, 2008, 01:48:31 AM »

Google is your friend....

Do a google using your part description as the search.  
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KB9CRY
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« Reply #2 on: November 03, 2008, 01:55:02 AM »

Mauser, Digi-Key, Ebay ?
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W8JI
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« Reply #3 on: November 03, 2008, 03:10:30 AM »

Nathan,

Relays like that, not common even when used when tubes were around, are now very very rare. Your only chance is a surplus relay.

A typical ~12 volt 50 mA relay has a 250 ohm coil resistance. To be a 5 mA 300V relay, the relay coil resistance would be in the 60,000 ohm range. I suspect you have a typical "plate circuit relay" which would be around 2000-10,000 ohms coil resistance.

Your best bet might be to look for a similar piece of gear or to build a solid state "converter" with an optical isolator. An opto-isolator will trigger with 5 mA and then you could use a regular 12V relay, commonly available at the sources others mentioned.

73 Tom

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W6OU
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Posts: 184




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« Reply #4 on: November 03, 2008, 10:43:09 AM »

I have a HP608C I am parting out. If you describe where the relay is and what is involved in removing it I can check to see if I have it and if it works.
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WB2WIK
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« Reply #5 on: November 03, 2008, 01:44:41 PM »

That was an option on the 608 and most 608s don't have the 3v output switch (relay).

Do you really need 3v output from it, or is this just to try to keep the unit "as original?"

I rarely use a signal generator at more than 1v...

I haven't looked at the 608 manual in many years, but does the generator still meet its harmonic/spurious specs at 3v output?  Somehow, I don't think it did, but must admit that instrument was designed when I was in second grade or so.

:-)

WB2WIK/6
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NR5P
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Posts: 131




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« Reply #6 on: November 04, 2008, 04:43:20 PM »

Just want to keep it original.  I don't think I'll need the 3v output anytime soon but just like to keep it fully operational.  The relay is under tube v4 look from top and find v4 and if you flip it over you'll see it within a few inches.  Let me know if you have it.  Thanks, nathan
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NR5P
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« Reply #7 on: November 04, 2008, 04:52:04 PM »

I meant to say its an hp606.  I got the model number confused with my other.  Sorry.  
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WA6HDZ
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« Reply #8 on: November 04, 2008, 05:00:48 PM »

You can try to rewind the relay coil, it's usually nothing more than many hundreds of turns of fine wire.  You may get lucky and have the open break very near the terminal.  But the optocoupler is the way to go if you''re really planning to use the beast, and there is plenty of room in a 608 to mount a small PCB. Also, whatever you do, check the tube that ran the relay- a heater/cathode or anode/cathode short may have been what killed the relay coil.
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