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Old 26th Sep 2019, 8:09 pm   #49
DonaldStott
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Join Date: Aug 2015
Location: Glasgow, UK.
Posts: 921
Default Re: Kolster-Brandes MR10

A huge thanks once again to David Taylor (David G4EBT) for advice and guidance on how to identify the problems with this 12AT7 valve.

So what we found was that if you remove the valve and check on a low Ohms range first between pins 4 & 5 of the valve itself, then between 4 & 9 and 5 & 9 you get a reading of 1 - a short/open circuit?

Then with the valve back in place, the set turned on and switched to FM, checked if there was 6.3V AC between pins 9 & 4 (or 9 & 5). Got a reading of 6.5V AC so at least V1 is getting a heater voltage?

Can we therefore conclude that we have a duff valve?

If I do need to replace this valve should I just go for a like-for-like 12AT7 or go down the route of swapping it for an ECC81?

No matter which one is chosen, there are many variations of both of these valves so some further advice and guidance would be welcomed?
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