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 Post subject: Hickock TV-7/u Help
PostPosted: Feb Fri 15, 2019 4:25 pm 
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Joined: Feb Fri 15, 2019 4:19 pm
Posts: 3
I'm having a problem with my TV7u tester. It's been a good tester with no problems for a year or so. Yesterday when I used it the mutual conductance switch (#3) stopped working. When the switch stopped working it was intermittent at first. We tested the meter with line adjustment and it was still working. We're not sure if this something we can fix or if we need to send it to be repaired. Any help or advice would be very appreciated.


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 Post subject: Re: Hickock TV-7/u Help
PostPosted: Feb Sat 16, 2019 1:43 am 
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Joined: Jan Thu 24, 2019 1:22 pm
Posts: 47
Location: Centennial, Colorado 80122
The #3 mutual conductance switch does 2 things 1 it applies plate voltage to the tube being tested and 2 it applies screen voltage to the tube being tested if the tube has a screen grid. The type 83 gas rectifier tube supplied the DC plate voltage and if it failed that could be your problem. The type 5Y3GT tube supplies the bias and the DC screen voltage. To simplify things try testing a triode tube, which does not have a screen. If you do not get any indication, then its likely in the plate supply. Its very unlikely to be the switch, since the switch is a DPST and if one set of contacts was not making it would drive the meter up or down scale. If you have access to a type 83 tube I would sure give it a try, but it being intermittent before not getting any indication is problematic. Maybe this will get other ideas flowing.


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 Post subject: Re: Hickock TV-7/u Help
PostPosted: Feb Sun 17, 2019 5:52 pm 
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Joined: Feb Fri 15, 2019 4:19 pm
Posts: 3
Thanks for this information, it's very helpful! We were testing a 6SN7 tube when it began failing. We'll check the Type 83 tube.


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 Post subject: Re: Hickock TV-7/u Help
PostPosted: Feb Tue 19, 2019 2:50 pm 
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Joined: Jan Mon 28, 2013 9:35 pm
Posts: 1311
Location: Santa Rosa, CA
What happens if you try to set the LINE voltage?
If you are getting no meter reading check the meter
rectifiers. Had the same symptoms you did and the
rectifier stack was making poor contact with its frame.

Also consider pinched wires as thats very easy to do
when putting the chassis in its case.

At the very least I'd take the chassis out of the case
and look for obvious things like loose wires or burned parts.
Steve

_________________
'cell phones and the internet are tools, not a lifestyle'


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 Post subject: Re: Hickock TV-7/u Help
PostPosted: Mar Fri 08, 2019 1:22 am 
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Joined: Feb Fri 15, 2019 4:19 pm
Posts: 3
Thanks everyone for your help. I thought I should check back in and let you know what we learned. We tried replacing the 83 tube and that did the trick. :D Thanks again for the advice and help!


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