Resistance Check Help

rdonahue · 1985

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Offline rdonahue

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on: January 02, 2017, 09:53:22 AM
I completed the resistance check on my Crack build and am getting two numbers that aren't right. Terminal 13 I am getting 0Ω and on terminal 22 I am getting anywhere from 9 to 35Ω.

(https://c3.staticflickr.com/1/300/32020841306_bc7bb056b3_c.jpg)
Bottlehead Crack by Ryan_D, on Flickr

(https://c4.staticflickr.com/1/300/31941945291_63214252da_c.jpg)
Bottlehead Crack by Ryan_D, on Flickr



Offline fullheadofnothing

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Reply #1 on: January 02, 2017, 10:29:40 AM
You are missing the nuts on your transformer. You also appear to have prematurely installed the tubes, which could influence your resistance readings. Fix these issues and remeasure.

Joshua Harris

I Write the Manuals That Make The Whole World Sing
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Offline rdonahue

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Reply #2 on: January 02, 2017, 10:58:30 AM
Okay, I've removed the tubes and installed the nuts. Now I am getting 0Ω at 22 which is good. Terminal 13 is odd though. When I first measured it it was reading around 12MΩ and went down to about 8.8MΩ. I removed the probe, waited a few seconds and tested again. It started around 8.2MΩ and went down to the low 7's. Then I took the probe off, waited again and re-tested and it was reading 6.9MΩ and continued to decrease.



Offline fullheadofnothing

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Reply #3 on: January 02, 2017, 11:11:41 AM
Quote
The values signified with a * are going to vary from ohmmeter to ohmmeter because these terminals are connected to the filter capacitors, which try to charge themselves off the battery in the meter, causing a fluctuating reading. If the circuit is connected properly these readings will wander in the tens or hundreds of Kohms or higher range. What you want to watch out for is a zero reading at one of these terminals, which would indicate that something is mis-wired.

Joshua Harris

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Offline rdonahue

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Reply #4 on: January 02, 2017, 11:19:19 AM
I figured this might be the case, I was just unsure since the manual states that the value of this terminal will "climb slowly towards 270k ohms" and I seem to be getting the opposite of that.



Offline Doc B.

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Reply #5 on: January 02, 2017, 12:13:30 PM
Someday we will have to change the manual to say

If it's not 0, it's the correct value.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.


Offline rdonahue

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Reply #6 on: January 02, 2017, 12:16:33 PM
Thanks for the replies Joshua and Doc. I just wanted to confirm before I go ahead with the voltage checks. This being my first high voltage project I wanted to make sure everything was good before I proceed.



Offline fullheadofnothing

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Reply #7 on: January 02, 2017, 12:46:02 PM
Someday was several months ago. This is an old Crack with the old manual.

Joshua Harris

I Write the Manuals That Make The Whole World Sing
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Offline rdonahue

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Reply #8 on: January 02, 2017, 04:57:08 PM
Well, that was exciting. I began the voltage check but had a nice little fireworks display when checking T1. I'm thinking that my hand slipped from T1 to T2 as I looked over at the meter. A large spark and a blown resistor but I'm still alive and kicking (new pants may be required however  :P)

I'm going to place an order w/ Mouser for a new resistor and pick up some extras of other common resistors, capacitors, LEDs, and such while I'm at it.

(https://c8.staticflickr.com/1/672/31257411103_de83d36390_z.jpg)
Blown Resistor by Ryan_D, on Flickr



Offline rdonahue

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Reply #9 on: January 03, 2017, 10:37:43 AM
Can I get a quick confirmation to make sure that this resistor will work  as a replacement that I burned up at 1U / 2U. The only difference being that it is 1W instead of 3/4W.

Metal Film, 22.1 kohm, 500 V, Axial Leaded, 1 W, ± 1%



Offline fullheadofnothing

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Reply #10 on: January 03, 2017, 10:45:02 AM
Have you measured the resistor to confirm that it's damaged?

Joshua Harris

I Write the Manuals That Make The Whole World Sing
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Offline rdonahue

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Reply #11 on: January 03, 2017, 11:13:21 AM
I'll check this evening but since it has a large black burn mark (you should be able to make it out in the picture) on it where the spark came from, it's probably wise to replace it.



Offline Paul Birkeland

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Reply #12 on: January 04, 2017, 07:58:06 AM
That resistor will work fine as a substitute.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline rdonahue

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Reply #13 on: January 04, 2017, 09:26:53 AM
That resistor will work fine as a substitute.

Thanks, I'll go ahead and order some as well as some other common value components to have as spaires.

As per Joshua's suggestion I checked the resistor and it is still reading 22.2kΩ. Would you guys suggest re-doing the voltage check or is there something I should be looking for that would have caused the spark?



Offline Deluk

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Reply #14 on: January 05, 2017, 02:59:12 AM
The soot on the resistor is a by product of the spark and may wipe off.. I would suspect that there is no actual electrical damage. I would just, CAREFULLY, recheck the voltages. There is some quite bad heat damage to a wire close by but again probably OK as there is no wire showing.