Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: rdonahue on January 02, 2017, 09:53:22 AM
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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) (https://flic.kr/p/QMzbwN)
Bottlehead Crack (https://flic.kr/p/QMzbwN) by Ryan_D (https://www.flickr.com/photos/rdonahue/), on Flickr
(https://c4.staticflickr.com/1/300/31941945291_63214252da_c.jpg) (https://flic.kr/p/QEAPuF)
Bottlehead Crack (https://flic.kr/p/QEAPuF) by Ryan_D (https://www.flickr.com/photos/rdonahue/), on Flickr
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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.
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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.
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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.
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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.
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Someday we will have to change the manual to say
If it's not 0, it's the correct value.
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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.
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Someday was several months ago. This is an old Crack with the old manual.
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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) (https://flic.kr/p/PC7pk6)
Blown Resistor (https://flic.kr/p/PC7pk6) by Ryan_D (https://www.flickr.com/photos/rdonahue/), on Flickr
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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% (http://www.newark.com/vishay/ccf6022k1fke36/metal-film-resistor-22-1kohm-1w/dp/71M1121?aa=true&vw=&categoryId=800000005308&eq=N%3D216953%2B422%2B810005182%2B2203%26amp%3BNs%3DP_STORE_MARKETING_RANK_NEWARK_US%257c0%257c%257cP_MAN_PART_NUM%257c0%26amp%3BNtpc%3D1%26amp%3BNtpr%3D1&searchView=table&iscrfnonsku=false)
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Have you measured the resistor to confirm that it's damaged?
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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.
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That resistor will work fine as a substitute.
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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?
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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.