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Author Topic: ts-520 final bias problem  (Read 1467 times)
NR5P
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Posts: 133




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« on: September 29, 2012, 03:08:48 PM »

I have a ts-520 and the final bias won't drop below 70ma.  It uses no current under receive so the receive bias supply and tubes must not be an issue.  I did check the rectifier voltage and the cathode resistors.  I get no plate current on receive and under transmit I can adjust it over 70ma but can't get it to drop to the 60 ma required.  I've been looking at the schematic but it only shows the rf board section of the schematic vr1, 2, and 3 I understand from tracing down are the pins on the variable bias pot.  I'm guessing an output on the rf board goes to the relay (which I have cleaned) and this relay would change the bias no the 6146's grids for receive.  Is there anything else to look at?  I've checked the pot and it is fine.  Which resistors on the rf board would most likely be the cause?  thanks
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K4EZD
Member

Posts: 100




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« Reply #1 on: September 30, 2012, 06:15:43 PM »

I don't have an answer but here is the link to the Yahoo Group that specializes in the TS 520 and has 3198 members with the answers that you may need.

http://groups.yahoo.com/group/TS-520_820_530_830/

Good luck.



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WB2WIK
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Posts: 20636




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« Reply #2 on: October 01, 2012, 03:35:55 PM »

70mA isn't very high.

What's the HV read on the meter (switch in HV position)?

What's your AC line voltage?

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AD4U
Member

Posts: 2179




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« Reply #3 on: October 01, 2012, 04:33:10 PM »

The bias pot should be able to adjust idling current from 0 up to at least 100 mA.  However using the rig with 70 mA idling plate current is OK and will not hurt the rig as long as every thing else is up to snuff.

Dick  AD4U
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