On Thursday, March 20, 2014 12:16:03 AM UTC-4, wrote:
I found this circuit somewhere, (I can't remember) to replace the 1.50 volt battery in a VTVM. I have an RCA WV98C Senior Voltohmyst VTVM that is in perfect condition but doesn't get used very often. This battery retrofit circuit takes power from the 6.30 volt filament transformer and is built around an LM317. With a trim pot you set it for 1.55 volts and you never have to change a battery again. It also needs to occupy an area no larger than the battery presently does.



As much as I like keeping things original, I'm worried that the battery is going to leak and rot the inside of the unit. I was going to build the circuit but it occurred to me that I should probably be concerned about the current that the LM317 will be dissipating when the meter is used on the low ohms range. Does anyone have a feel for the size that an adequate sized heat sink should be in order to handle this? Thanks, Lenny

I do own several digital voltmeters and they do have their place. You can't beat a digital for making precise measurements. But there is a bit of a sentimental value here too. I built this meter from a kit when I was a kid in 1963. Since then I've repaired a lot of TV sets and other things with it over the years, and although I don't use it much anymore it's nice to still be able to when the need arises. So just where the hell do you come off insulting me?

I'm just curious now. Did you ever try to peak or null a circuit with a digital? It's a pain in the ass. How about looking for a change in logic state? I prefer seeing an immediate change rather than watching a decay. Why don't you try going on the grid of a tube with a low impedance meter and see where that gets you? Mine has an 11 meg ohm impedance. It won't load a vacuum tube circuit. So much for my piece of **** meter, huh?

But I have a better idea Trevor. Why don't you take your prize digital you've raved about and stick it in your ass? That way you'll never lose it, and it will always be available. Lenny