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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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17th Sep 2017, 10:32 pm | #1 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
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Substituting 12AT7/ECC81 in place of 12AU7
Back on my VTVM project for an evening and I've just blown up the 12AU7, fortunately a Chinese cheapy. They don't like 170V DC across the heater. That'll teach me to use yellow wire for everything. Oops! I also can't find the replacement one I bought just in case I blew that one up. Double oops!
Now on with the show, I've got a large box of valves here I picked up at a boot sale a month or so ago which contains a few Mullard and Philips ECC81s that the heater tests good on. That's a 12AT7 if I'm not mistaken. As I am devoid of anything that looks similar, is this is a suitable substitute for the 12AU7 in a VTVM role i.e. simple differential amplifier? |
17th Sep 2017, 10:43 pm | #2 |
Banned
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,897
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Re: Substituting 12AT7/ECC81 in place of 12AU7
Should do, ECC81 is the lowest gain of the ECC series.
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17th Sep 2017, 10:43 pm | #3 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,427
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Re: Substituting 12AT7/ECC81 in place of 12AU7
The ECC81 is an RF valve with higher mutual conductance and amplication factor but it shouldn't cause any damage, perhaps may need some work to keep it stable.
Edit. Sam I must have read the specs wrong, it is late.
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Frank |
17th Sep 2017, 11:13 pm | #4 |
Heptode
Join Date: Jan 2006
Location: Todmorden, West Yorkshire, UK.
Posts: 870
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Re: Substituting 12AT7/ECC81 in place of 12AU7
The ECC82 has an amplification factor of 20 ; the ECC81's is 60. ECC81s do have higher transconductance but it's not massive so you shouldn't have any oscillation problems. They were often used as phase splitters in audio amplifiers .
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17th Sep 2017, 11:36 pm | #5 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
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Re: Substituting 12AT7/ECC81 in place of 12AU7
Thanks all. Will chuck it in and see what happens!
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18th Sep 2017, 12:27 am | #6 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
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Re: Substituting 12AT7/ECC81 in place of 12AU7
Well it works with it in and it's quite jumpy now. Will order another 12au7 and see how that goes too. Thanks again
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