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Help with Cossor 1044k VTVM
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Return to top of page · Post #: 1 · Written at 10:06:33 PM on 6 November 2014.
	Kxdniu Location: Melbourne, VIC Member since 19 May 2014 Member #: 1577 Postcount: 101
Hi, I got a Cossor 1044K VTVM from eBay. After replaced rectifier and filter cap, it works. However, it is not very accurate. I couldn't find a circuit for it. I know it is similar to Heathkit V-7A, but the AC input is different. Does anyone has some info about it? I try to fix it and use it for my radio works. Regards Kevin

Return to top of page · Post #: 2 · Written at 11:33:01 PM on 6 November 2014.
	GTC Location: Sydney, NSW Member since 28 January 2011 Member #: 823 Postcount: 6761
It may be poorly calibrated, however are you allowing it time to warn up and stabilise before using it?

Return to top of page · Post #: 3 · Written at 11:40:29 PM on 6 November 2014.
	Marcc Location: Wangaratta, VIC Member since 21 February 2009 Member #: 438 Postcount: 5389
It also may be like an AVO 7X and a huge variety of radios & have wax paper capacitors in it as well, and they will have to go. I mentioned 7x as had paper caps & one was common to DC 400V range which was thrown off accuracy swiftly by it. Marc

Return to top of page · Post #: 4 · Written at 7:38:47 AM on 7 November 2014.
	Kxdniu Location: Melbourne, VIC Member since 19 May 2014 Member #: 1577 Postcount: 101
Yes, I did let it warmed up for half an hour. There is only one capacitor in it that may be a paper one. It is the ac input capacitor. I haven't replace it, as I don't have a high voltage rating one. By the way, any info about from where to get a 1500v capacitor? Thanks guys.

Return to top of page · Post #: 5 · Written at 9:54:23 AM on 7 November 2014.
	Marcc Location: Wangaratta, VIC Member since 21 February 2009 Member #: 438 Postcount: 5389
You can get a "red" green cap at 2KV and there are TV types that go into KV. Try RS components. I nobbled the old Heathkit CRO here when refitting by raising the input caps to 2KV. What we do need to know is if the voltage is correct on the valve/s and these can get tired & loose emission and are not as yet confirmed as being the right ones. It was a Kit so is likely just a re-badged Heathkit http://www.radiomuseum.org/r/cossor_valve_voltmeter_1044k.html I have the circuit of the Heathkit.... what is different about the AC input? Viz electical or cosmetic? Marc

Return to top of page · Post #: 6 · Written at 11:22:18 AM on 7 November 2014.
	Kxdniu Location: Melbourne, VIC Member since 19 May 2014 Member #: 1577 Postcount: 101
Hi Marc, The common VTVM ac input circuit has one dc blocking cap in front and then three resistors for different input voltages. This VTVM uses a low rating cap. For 1500v ac, the circuit has a 2.85m resistor in front, then the cap, next are two resistors. Also it uses two extra caps in the bridge circuit. That's why I hope someone can give me some info about it. It's similar to v-7a, but not the same. I will try RS components, thanks Kevin

Return to top of page · Post #: 7 · Written at 4:46:12 PM on 7 November 2014.
	Marcc Location: Wangaratta, VIC Member since 21 February 2009 Member #: 438 Postcount: 5389
One option is to have a look at the Heathkit circuit print it & then make the mods to suit yours. This is a Kyoritsu or something variant... Marc

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