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Thread: 12SN7 vs 6SN7 in a Croft pre question.

  1. #11
    Join Date: Apr 2012

    Location: London

    Posts: 331
    I'm james.

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    My understanding is that pinouts are given from below the valve as if when wiring the socket up. So Lawrence I'd be looking to measure the two pins anticlockwise from the key. And remember filaments might be running on ac so if dc values are really weird try ac values!

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  2. #12
    Join Date: Dec 2017

    Location: Ontario, Canada

    Posts: 43
    I'm Dan.

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    PS I think your 2 statements about the pin outs are contradictory.
    Looking from the top, 7 and 8 would be the last two pins anti-clockwise from the key. From under the chassis looking at the bottom you go clockwise the last two pins.
    Jazid is also correct, the filament could be AC or DC. The attachment is the pin out from the bottom (wiring side)
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    Dan Santoni

  3. #13
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 1,582
    I'm Lawrence.

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    Ah ok I was measuring assuming the pin out was from above. I didn't imagine the valves would have lasted long with 80v across the filaments! I'll try tonight.

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  4. #14
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 1,582
    I'm Lawrence.

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    All sorted now, it measured 11.1v on both valves so as I suspected from the heat it's designed for 12SN7. This was a surprise as I've never heard of a Croft amp built around this valve. I'm pleased on 2 fronts - the 12sn7 are as good sounding but cheaper, and I do like a rare piece of equipment

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  5. #15
    Join Date: Dec 2017

    Location: Ontario, Canada

    Posts: 43
    I'm Dan.

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    I'm glad you got that sorted out. Running the 6SN7 at that voltage would change its characteristics and they would have a very short life.
    Dan Santoni

  6. #16
    Join Date: Apr 2012

    Location: London

    Posts: 331
    I'm james.

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    I'd ask Glen, he will remember an oddity of his own making. Top chap, he will help you and yes, I agree, 12sn7 is a bonus

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  7. #17
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 1,582
    I'm Lawrence.

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    Thanks guys that's where this forum and the experience of those on here really comes in handy, stops you blowing up your nice new equipment!! It wasn't just the heater voltage I found out about, also the rectifier was not in properly and another voltage supply valve was glowing like a light bulb.

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    Last edited by Lawrence001; 25-05-2018 at 11:05.

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