Zenith 852-120 HV probe repair
 

Forget it. I no longer have the probe anyway, and I'm not going to fight with anyone, especially with hotheads who have offended me repeatedly and without cause.

There are only two people who help me regularly anyway, and I don't need the board to contact them.

Shouldn't be any problem using 1W metal oxides. Couple of questions - Did you suspect the probe of reading high, or low?

In your schematic, you show a shunt across the paralleled 30K and 33K resistors. Is that shunt supposed to be there?:saywhat:

I was just about to say... that shunt would negate the 2 resistors on the far right. In fact... why are they in parallel? Wouldn't that be like... (33+30)/2 = 31.5kohm? Oddly specific value. You sure your schematic is right?

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Your math is wrong (should be ~15.7K). Two resistors in parallel are Req=(R1*R2)/(R1+R2) Three or more are Req=1/( (1/R1) + (1/R2) + ... + (1/Rn) )

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Only if they are both rhe same value.

jr

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The equation simply says that 1/R = 1/R1 + 1/R2 and to continue adding them up for as many resistors (n means number of resistors) as you have in parallel, that's all that ....+ stuff in the mathematical series means. Do you have a calculator that inverts?

My guess is that the shunt and the two resistors across it are to be used in calibration and can be clipped out if necessary by the calibrator if the calibration pot does not have adequate range.

Why do you think the meter reads low, have you measured a known voltage standard?

jr

The only reason I can think of for the shunt is that maybe this assembly was also used in another probe model where the shunt was replaced with a switch to change the meter full scale reading.

BTW, your schematic does not show the huge resistor that is in the probe body.

Another thing, the 2.2M is apparently only a current-limiting safety provision and does not affect calibration.

It was 1 am dude, cut me some slack.

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Then you are assuming that the meter is wrong because it indicated that the HV on a few old TV sets was low? Vintage TVs are hardly what I would call "voltage standards" .

jr

I've seen videos made by Doug in which his meter measured accurately. Mine wouldn't even register on a tripler focus tap. Only saying this because the mods ignored my delete request which doesn't surprise me or help my opinion of them. It's not what you know but who you know.

Nothing like having a know-it-all bully around to pick apart my efforts. Now, can the patronizing attitude and go back to tube town.

I can understand doing 'sleep deprivation math' (college had me doing plenty :D )....I was not trying to criticize; Just trying to help with the correct formula(s).

You know, I don't really know anybody around here, but I get the distinct impression that none of them are really 'internet people.' Because communicating information and emotions and attitude effectively in the written word (vs verbally) takes a certain amount of experience... and quite frankly I see little of that here.

May we go back to discussing the probe repair, or are people going to insist on misinterpreting posts and having a fight?

I saw nothing patronizing, nor any reason to bar the discussion for those who are correctly or incorrectly perceived not to have SS experience. Both types of sets have high voltage.

Not my thread - and your point is valid - but telling people to shut up and move on is not really helpful in these situations. A modicum of patience and understanding might actually help prevent these misunderstandings... because it's starting to look like this is a common issue.

Where were we on that probe repair? Oh yeah, op deleted all the posts. Um... is there maybe something to benchmark the voltage readings against?

You came asking for advice, and he joined in on this thread offering to help you.

Where's the bullying?

I only see you as being very rude here, probably from some grudge you have had with him in the past.

Now you took your marbles and went home because things didn't go your way? That's not very productive if you want anyone's help in the future.

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