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Author Topic: drake tr3 .33mf cap looks like resistor!  (Read 1366 times)
KC9VZB
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Posts: 45




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« on: January 02, 2013, 07:55:23 PM »

I'm going over parts while waiting for my turn on net. changed a few paper capacitors.Checking high value resistors,I found a little short,fat 33meg that showed open,I didn't have one so I soldered 3 -10 megs to make 30 and stuck it in there,turned the power on,and no difference!So I puzzle out schematic and it shows it to be a .33mf.This fix is teaching me a thing or two.Again.My high voltage is higher than specks like 40-50 volts,I thought more is always better.I adapted a heath supply.Could excess b+ cause tubes to cut off?I guess I'll get a resistor in there to back it down,maby in the supply there's a adjustable clamp type.
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W9GB
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Posts: 2597




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« Reply #1 on: January 02, 2013, 08:26:36 PM »

Replacing Capacitors in Old Radios and TVs
http://www.antiqueradio.org/recap.htm

Strategies to Repair or Replace Old Electrolytic Capacitors
http://www.nmr.mgh.harvard.edu/~reese/electrolytics/

Capacitor color codes
http://www.electronics-tutorials.ws/capacitor/cap_5.html
« Last Edit: January 02, 2013, 08:29:25 PM by W9GB » Logged
N4NYY
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Posts: 4742




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« Reply #2 on: January 03, 2013, 08:34:40 AM »

Occasionally, I come across a component that I cannot identify. I think early ceramic caps may pass for resistors or vice versa. In this case, I use the knowledge of AC5UP who has a wealth of experience because he is 100 years old. G3RZP, N2EY, and several others help me when needed.
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W4OP
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« Reply #3 on: January 03, 2013, 09:15:30 AM »

.My high voltage is higher than specks like 40-50 volts,I thought more is always better.I adapted a heath supply.Could excess b+ cause tubes to cut off?I guess I'll get a resistor in there to back it down,maby in the supply there's a adjustable clamp type.
______________________________
I would run the rig at spec voltages.
Remember, when these supplies were built, the A.C. mains were around 110VAC. Now they run 120 and higher. Measure your filament voltage- it is likely high too. That means more heat and shorter tube life.
I built a bucking transformer for my vintage gear to reduce the mains back to 110 VAC.

Dale W4OP
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KB4QAA
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« Reply #4 on: January 03, 2013, 09:23:52 AM »

I think the other lesson here is: Always compare the Schematic, the Parts List, the Actual Component markings and measurements before replacing.
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G3RZP
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Posts: 4360




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« Reply #5 on: January 03, 2013, 10:15:46 AM »

And in the case of the FT102, try to make a correlation between them all!
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N4NYY
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Posts: 4742




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« Reply #6 on: January 03, 2013, 10:48:22 AM »

I think the other lesson here is: Always compare the Schematic, the Parts List, the Actual Component markings and measurements before replacing.

They don't always match your. Revisions or bulletins did not always make it to the schematic.
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