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Old 26th February 2011, 04:21 AM   #1
exurbia is offline exurbia  Australia
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Default Type 40, 12A, 112A(syl)

Hi tubees,
Just a general question.
Has anyone tried the 40,12A,112A tubes in a preamp ?

I have a few of each left in my caddies.
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Old 26th February 2011, 06:11 AM   #2
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Hi!

These are all diectly heated. 12A and 112A ae the same tube in different shapes. These two can be used in preamps. However care needs to be taken to control microphony. Also to use them right takes quite some effort and expense. See 26 preamp thread for such preamps. 40 has way to high plate resistance for audio circuits

Thomas
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Old 26th February 2011, 10:32 AM   #3
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Yes - I've tried the 12A but not the 40. I always found the 12A sounded just that bit less good than the 26 or 01a, so I've never really bothered with it. It's not a bad tube at all, but I'd use a 26, or a 10Y.

So go directly to the "26 pre amp" thread. Do not pass GO. Do not collect $200.

andy
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Old 26th February 2011, 10:49 AM   #4
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Hi Andy,

although the 12 and 26 seem to be quite similar, if they sound different in your preamp, I'd not necesarily see the cause in the tubes themselves. The 12 has a different filament voltage and current. Might as well be the filament supply which acts differently, or any other surrounding circuit.

I've built a universal linestage which can accept 01A, 12A, 26 and 801A/10Y. I did a public comparison at the Vienna Vibes festival last year. Although there were differences thes ewere mostly based on personal tastes. Some people preferred one tube some another.

For me the 12A was closer to the 26 as both of them to the thoriated filament types which always end up to be my personal preference. One person who had some more time to spend with my linestage even happend to prefer the 12A ... go figure

Best regards

Thomas
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Old 26th February 2011, 01:27 PM   #5
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Hi Thomas,

Yes, you never really know about listening experiences, though we try to be objective. Personally I listen for vocal and instrumental timbre - but I know some very capable audiophiles that listen for dynamics, total frequency response and soundstage respectively, and optimise their systems accordingly.

Hi-fi can be quite counter-intuitive. You design the "correct" solution and the incorrect solution sounds better. I used 12A as drivers in a PP 2a3 amp - lower plate resistance. I took it out and put in a couple of 26 and it sounded clearly better!! A friend of mine modified a Leak Stereo 20 to take 6N1P into 6N30 phase splitter in the front end. It sounded much better with 6N30 into 6N1P.

Andy
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Old 26th February 2011, 02:04 PM   #6
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Hi Andy,

Quote:
Originally Posted by andyjevans View Post
though we try to be objective.
I don't
Listening is always subjective.

I didn't want to question your findings. Only wanted to say that if a certian component sounds in a certian way in one circuit, it doesn't necessarily mean it will sound like that everywhere.

Best regards

Thomas
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Old 26th February 2011, 11:49 PM   #7
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Hi Andy and Thomas,

Thanks for the info and opinion. I won't be building with the 12's or any other dht at present. I asked as I have a few boxes of smaller valves left over from my sale, there are quite a few dht's in them plus indirects like 27,37 and variants plus a few Cardons.
just wondering if there was any point in keeping them.
Cheers,

Peter.
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Old 27th February 2011, 12:06 AM   #8
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Hi Thomas,

Oh the trials of optimising a circuit! I just spent all evening switching between a 71a and a 31 into a Hammond 126C interstage as the driver stage in my 300b SET.

The 31 sounded lovely. The 71A sounded crap. Opposite of what I expected. Eventually you find good combinations between tubes and iron. Takes time though!!

Andy
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Old 27th February 2011, 06:39 AM   #9
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Hi Andy,

if there was such a big difference and one of the tube sounded like crap, something is seriously wrong. With the circuit that is, not the tube!

Have you done some measurements? If something sounds like crap that is often very visible on the scope. Those two tubes have different plate resistances. Probably the interstage transformer was ringing with the 71A or had some resonant peaks in the audio band. Such peaks can sound very un pleasant.

Best regards

Thomas
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Old 27th February 2011, 11:03 AM   #10
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I don't think it was a resonance - the sound was just thin and uninviting and with the 31 it filled out and became musical again.

I have a scope but don't yet know how to use it. I keep putting off learning - foolish I know. I'll need it to get things really right.

Andy
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