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Old 26th February 2014, 03:03 AM   #1
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Default ST Triodes?

I am curious which ST bottle tubes are good for hifi use. I prefer the look of these tubes and will use them when I can. It is important that the tubes be affordable (<$20 each), fairly abundant, and good performing. I know of the following ST preamp/driver tubes:

IDH Triode
27/37
56/76
6L5

IDH Dual Triode (common cathode)
6N7/6Y7/6A6/53

Of course, there are options for output tubes as well but I am looking for preamp/driver tubes at the moment. What are the other options?

Thanks!
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Old 26th February 2014, 08:17 AM   #2
euro21 is offline euro21  Hungary
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Why primarily IDH triodes?
Direct heating tube's tone -IMHO- is far better (26, 10Y/VT25, 801/VT62, 2A3...).
These are all ST tubes. :-)
But....globe version of these tubes even better.
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Old 26th February 2014, 09:40 AM   #3
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+1
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Old 26th February 2014, 12:32 PM   #4
TheGimp is offline TheGimp  United States
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One thing to bear in mind with common cathode twin triodes is that many were designed to support class B operation.

They are designed to handle grid current as the grid goes positive relative to the cathode. This requires a heavier grid structure than a tube of the same function which is not designed for class B operation.

I expect this will have some impact on distortion profile, and would not be surprised if they had higher distortion as a result of the design tradeoffs made.

For class A, they were recommended as driver tubes using transformer coupling.

Why would the globe tube sound better than the ST if the electrical structure were the same? Or, did the manufacturers change the electrical+ structure when changing to the ST package?
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Old 26th February 2014, 01:42 PM   #5
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Quote:
Originally Posted by TheGimp View Post
Why would the globe tube sound better than the ST if the electrical structure were the same? Or, did the manufacturers change the electrical+ structure when changing to the ST package?
There is one difference: ST tubes have an upper mica support, touching the glass. Globe tubes don't. Therefore, the microphonic response to external vibrations is not the same.
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Old 26th February 2014, 02:52 PM   #6
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IŽve used the 27 and the 56, they are very good, just make sure to buy a couple extra so you can select the least microphonic. IŽd also recomend using rubber washers to mount the sockets.

The 6N7 is a good tube and is very linear, class B has nothing to do with its linearity. For example the 46 is designed for class B yet in triode mode it is easily one of the most linear tubes youŽll find. To see the curves at negative grid voltage (youŽll usually find just the positive grid region) use this russian datasheet:

http://www.mif.pg.gda.pl/homepages/f...113/6/6N7S.pdf

If you want compactness go with the 6N7 since you get 2 triodes per envelope.

As far as other ST or S (globe) triodes go check out these:

mu rp
71A 3 1700
12A 8.5 4700
01A 8 10k
26 8.3 7600

They are all filamentary tubes and reportedly sound "better", IŽm going to use the 01A in my next amp. It has a thoriated tungsten filament so it glows much brighter than the dull red oxide coated, if looks matter to you IŽm sure this is a big plus, have a look at it. Also remember that you can always triode strap pentodes/tetrodes which will widen your selection.

If you want a really cheap tube, try triode strapped 24 (the have a grid cap though), lots of 5 in ebay sell at around 20$. It has mu 11 and rp 11k in triode.
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Old 26th February 2014, 02:56 PM   #7
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I do hope to move to DHT soon, but I am looking for indirect heating for my next amp since the output tubes are indirectly heated.

Globes would also be fine.
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Old 26th February 2014, 03:17 PM   #8
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My first ever tube project was a 71A linestage - I used early globe versions since they looked so cool. They were so microphonic that you could shout at the 71A and have it amplified enough that a strangely modulated version would come out of the speaker. My fellow tubo-philes thought it was great fun.

It did - however - sound good, provided you stuck the preamp in a closet or behind the sofa - anywhere away from the speaker output.
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Old 26th February 2014, 05:04 PM   #9
TheGimp is offline TheGimp  United States
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I understand the difference in mechanical and hence microphonic sensitivity for globe vs ST tubes.

I was wondering if there were any electrical changes that do not show up in the datasheets as some people claim the Globe tubes sound better, microphonics not withstanding.
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Old 26th February 2014, 06:13 PM   #10
Magz is offline Magz  United States
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I've also heard the explanation that mica tends to out-gas over time, thus the ST tubes end up with a bit poorer vacuum than the globes.
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