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 Post subject: Re: Jackson VTVM
PostPosted: Apr Wed 01, 2020 1:00 am 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 3964
Location: Florida
Before I saw the schematic I mentioned 6.3 because that's the nominal filament voltage specified for the tubes. The schematic shows 5.7 which is what Jackson used for the design, so I'd stay close to that or a little above. If you use a resistor that gives 5.7 at your location that should be OK, although if it were my meter I'd probably use 5.9 or so just to keep it a little closer to the nominal of 6.3 in case the voltage drops a little.

That 100-125 is what I was looking for.

Look, we're not talking about a lab instrument and ballast tubes aren't precise regulators so unless things are way out of line all should be OK. I'd get things in the right ball park and go for it.

RRM


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 Post subject: Re: Jackson VTVM
PostPosted: Apr Wed 01, 2020 1:57 am 
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Joined: Nov Sat 24, 2012 5:05 am
Posts: 137
Location: Forest Lake, MN 55025
Thanks DM, I reread your post and see what you mean, I put 80VAC on the input to transformer primary and it gives me 145VAC on the rectifier plate and 5.55VAC on the filament so i think I am pretty close and agree that 40 volts needs to be dropped (120-80) and the current is 40ma. This gives me a 100 ohm 16 watt dropping resistor, I will use a 20 watt for safety. Thanks for the response.

ettore


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 Post subject: Re: Jackson VTVM
PostPosted: Apr Thu 02, 2020 1:55 pm 
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Joined: Nov Sat 24, 2012 5:05 am
Posts: 137
Location: Forest Lake, MN 55025
Thanks DM.

ettore


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 Post subject: Re: Jackson VTVM
PostPosted: Apr Thu 02, 2020 8:40 pm 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 3964
Location: Florida
Have you checked any functions or tried to calibrate while running off the variac?

RRM


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 Post subject: Re: Jackson VTVM
PostPosted: Apr Thu 02, 2020 11:39 pm 
Member

Joined: Nov Sat 24, 2012 5:05 am
Posts: 137
Location: Forest Lake, MN 55025
not yet my meter is bad and I have a 3A-20 tube on the way. One step at a time. Appreciate all the input.

ettore


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