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!
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!
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?
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?
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.
I´ve 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. I´d 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 you´ll find. To see the curves at negative grid voltage (you´ll usually find just the positive grid region) use this russian datasheet:
http://www.mif.pg.gda.pl/homepages/frank/sheets/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", I´m 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 I´m 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.
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 you´ll find. To see the curves at negative grid voltage (you´ll usually find just the positive grid region) use this russian datasheet:
http://www.mif.pg.gda.pl/homepages/frank/sheets/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", I´m 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 I´m 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.
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.
It did - however - sound good, provided you stuck the preamp in a closet or behind the sofa - anywhere away from the speaker output.
All NOS ST DHT's are over $20 as are current production tubes like the 2a3.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.
I picked up 50 NOS 1626 for under $2 each a few months ago on eBay.
It's a pleasant sounding tube and a big improvement over the chipamp in my office which it replaced. That being said, you won't mistake this tube amp for a well designed DHT amp. I copied the original darling by Danielak, a well documented design.
I am familiar with the 1626, but didn't list it before since the mu is a little low for my needs.
On a completely different note... What does one mean by 'the graphs don't look very linear'? I know that 'linear' usually means the distortion spectrum falls so that 2nd, 3rd, 4th, etc. harmonics essentially look like a straight line. But, how does one see that from the datasheet?
On a completely different note... What does one mean by 'the graphs don't look very linear'? I know that 'linear' usually means the distortion spectrum falls so that 2nd, 3rd, 4th, etc. harmonics essentially look like a straight line. But, how does one see that from the datasheet?
You can see in the Vg -> Va/Ia graph if the distance between the curves doesn't change much, if at higher current the curves are almost straight and they remain relatively parallel (they don't fan out much).
You can also look at the Va -> Vg/Ia curves : you should use the tube within the linear part of this curve.
You can take a look at a 300B as an example of linear device, and at, say, a 12AT7 for a less linear one.
Here is an extreme case of a triode with poor linearity. It was specifically designed to have remote cutoff characteristics by varying the grid turn spacing to make the grid turns less dense at the ends and more dense in the center.
The 6386 is a remote cutoff triode.
http://www.mif.pg.gda.pl/homepages/frank/sheets/142/6/6386.pdf
It is possible to calculate the harmonic from measurements taken from the graph.
The 6386 is a remote cutoff triode.
http://www.mif.pg.gda.pl/homepages/frank/sheets/142/6/6386.pdf
It is possible to calculate the harmonic from measurements taken from the graph.
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