heath kit VTVM model v-7A

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heath kit VTVM model v-7A

Post by CHUCKSUE on Fri Feb 13, 2015 4:24 pm

It's dead in the water. Only the pilot lamp burns and the tubes. The schematic shows the voltages for the electrolytic capacitor. Has anyone worked on one of these? I have no meter movement at all. I am checking the wiring since I have the construction manual.

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Re: heath kit VTVM model v-7A

Post by Wildcat445 on Fri Feb 13, 2015 10:02 pm

I have very little experience fixing test equipment.  I had a Heathkit VTVM that went wonky last winter.  I even forget what the matter was just now.  There may be a thread on here about it.  I would suggest you check the voltages, since you have the construction manual, and, presumably a schematic.  Could you post the schematic so we can follow along?  This sounds like something fun to dig into.  Would you care to share?  Maybe somebody with more experience fixing test equipment will chime in.  Start at the rectifier and power supply and go from there.  Please keep us informed on your progress.  Good luck.

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Re: heath kit VTVM model v-7A

Post by CHUCKSUE on Sat Feb 14, 2015 4:52 pm

The meter was wired correct. I don't know how to post. What I found was the copper traces are lifted and broken. The 12AU7 was worst of all. I made a bracket to mount a 9 pin socket and it will mount above the rectifier and filter cap. I hope this works. I wired the meter with jumpers and it works ok. I will try to complete the tube installation and let you know.

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Re: heath kit VTVM model v-7A

Post by Wildcat445 on Sat Feb 14, 2015 4:59 pm

I recently worked on a GE stereo that had a fairly severe case of lifted traces on the PCB. I rewired the PCB chassis with hard wiring and it seems to have worked well. Perhaps a similar procedure would save your having to replace a tube socket. Good luck.

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Re: heath kit VTVM model v-7A

Post by CHUCKSUE on Sat Feb 14, 2015 5:05 pm

The tube socket is put thru a 3/4 inch hole. Then the socket pins are bent over the copper traces and soldered. This in my openion was a poor attempt to place a socket in a printed circuit board. Most that I have seen are pushed thru holes for each pin.

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Re: heath kit VTVM model v-7A

Post by Wildcat445 on Sat Feb 14, 2015 5:21 pm

As long as the socket is still secured to the board, I would think that hardwiring what was there might have been easier for you. There is no wrong way, though. Whatever works, and good luck.

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Re: heath kit VTVM model v-7A

Post by 75X11 on Mon Feb 16, 2015 4:49 pm

You might get more bites on your other test equipment items if you put a pic or two with each of them, also.
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HEATHKIT GENERATOR

Post by CHUCKSUE on Thu Feb 19, 2015 3:33 pm

I finally got it working. here are some pictures. The only thing I did not like was the zero adjust for AC/DC-/DC+. When I switch between them the zero adjust knob has to be tweaked. The manual says if it doesn't stay stable it is the 12au7 tube and it has to be left on for 48 hours in order for it to burn itself in????

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Re: heath kit VTVM model v-7A

Post by 75X11 on Thu Feb 19, 2015 4:42 pm

That kind of warm up is not uncommon for such a sensitive piece of test equipment. It's looking mighty good.
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Re: heath kit VTVM model v-7A

Post by Wildcat445 on Thu Feb 19, 2015 6:05 pm

I always considered it good practice and a necessity to zero adjust the meter each time the range or function is changed. Glad you got it going.

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Re: heath kit VTVM model v-7A

Post by Alan Douglas on Fri Feb 20, 2015 7:53 pm

The 48 hours was when the tube was new. It should have stabilized by now, but if the two halves aren't well balanced you could try some other 12AU7s.

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Re: heath kit VTVM model v-7A

Post by CHUCKSUE on Sun Feb 22, 2015 11:12 am

I have a few 12AU7 tubes. I will check them in my Hickok 800 first.

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Re: heath kit VTVM model v-7A

Post by 75X11 on Sun Feb 22, 2015 11:26 am

When you do use it, it is a good idea lo let it warm up and stabilize before you use it. At least 2 hours. That should reduce any drifting the meter may exhibit.
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