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 Post subject: Mercury Model 1000 Tester Problems
PostPosted: May Wed 07, 2003 9:05 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2
Hi!<P>I have a Mercury 1000 that gives lower and lower readings on the same tubes (12ax7s) as the unit warms up (15-30 minutes). Additionally, even on known good 12at7's it never gives anywhere near the 3300 mhos listed as the standard in the test list. On inspection inside, I note that two or three large white capacitors are cracked and leaking. Also at least one resistor is cracked. The tube inside does test good on my EICO 667, though close to the low side of green.<P>Now my question is, if I replace the caps and resistor, will I need to recalibrate, and if so, are recalibration instructions for this unit available on the net? There are about 5 or 6 bias pots inside, but none have ever been adjusted, as indicated by the red ink still intact on each.<P>Thanks much,<P>LMark<P>------------------<BR>


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 Post subject: Mercury Model 1000 Tester Problems
PostPosted: May Wed 07, 2003 2:34 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4444
Location: Connecticut. USA
Mark,<BR>I would replace all out of tolerence resistors and replace all caps.<BR>Don't worry about the calibration pots, they may be ok if they have not been touched.<P><P>------------------<BR>Bill Benson


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 Post subject: Mercury Model 1000 Tester Problems
PostPosted: May Wed 07, 2003 9:40 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 30698
Location: Pocasset, Cape Cod, MA
A change over 30 minutes suggests a heat-related problem. Perhaps a capacitor that increases leakage as it warms. The usual tool for finding such things is a can of freeze spray.<P>Without seeing the schematic, I'd guess that most of the caps and resistors have nothing to do directly with the Gm circuit, so there's little point in replacing everything blindly. I'd take it one step at a time, and check to see if the meter suddenly changes. If it doesn't, you won't have to twiddle any of the cal pots. But if you go replace all the parts, you'll never know what caused a Gm change.<P>------------------<BR>


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 Post subject: Mercury Model 1000 Tester Problems
PostPosted: May Thu 08, 2003 3:25 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 446
Location: Winnipeg, Manitoba, CANADA
I like my 1000, but it has its quirks. The schematic does not list calibration instructions, just the wonderful disclaimer that it has been done at the factory, so don't screw with it. Thanks. Some manuals I have seen for the 1000 state that the 44 bulbs are part of the gm circuit (just like B&K). I'd look at the bulbs, and maybe some cold solder joints. There is the dual section filter at the meter (200X200uF/10VDC), and the two bias filters (100uF/25VDC), so changing the electrolytics isn't too much of a big deal. I'd measure the bias voltage at start up and after 15 minutes, and see what's up. If the capacitors are bad, the bias voltage would actually decrease, and the reading would increase, so I think that ain't it. But check anyway, and see if bridging the capacitors brings the C- voltage up at all. I look at the bulbs and the meter if it was my 1000. The tube inside is for the gas test, if I remember rightly. <BR>Oh, shoot! CLEAN THE LEVER SWITCHES! CLEAN THE LEVER SWITCHES!<P>------------------<BR>


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