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Old 1st August 2014, 12:50 PM   #1
M Gregg is offline M Gregg  United Kingdom
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Default Sub minature tube gain stage question.

Does anyone know,

Of a sub miniature (solder connection) tube that can be used in a HIFI low gain stage using the standard HT voltages similar to ECC82 etc?


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M. Gregg
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Old 1st August 2014, 02:25 PM   #2
mwiebe is offline mwiebe  United States
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I’m not sure I understand this aspect of your request, “using the standard HT voltages similar to ECC82” unless you are looking to wire a sub-mini to a 9-pin base to just plug in with no other changes to a 12AU7 socket.

Your best single reference for sub-mini tube spec’s is Frank’s data pages, or in hard copy, GE’s Essential Characteristics data book.

Without knowing exactly what you are looking for, twin triode or not, here are a few you might want to look at with Mu around 12AU7. Russian sub-minis will probably be your best bet, many like the 6N16B, 6N17B, 6N21B, will safely take 200V or more on the plate. Single triodes like 6S26B, 6S27B, 6S32B, work to 250V.
Non-Russian tubes are usually spec’ed around 150V but can be used higher safely. Twin triodes like the 6021, 6111, 6BF7, and single triodes like the 5977, and there are plenty more.
The lower plate spec can be an advantage, allow direct connection without negative rails or excessive B+.
Matt
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Old 1st August 2014, 03:35 PM   #3
M Gregg is offline M Gregg  United Kingdom
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Hi thank's for the reply,

I'm looking at putting a Sub miniature in a 12au7 circuit.
I know it sounds a bit strange..
I want to use a 12au7 x4 line stage circuit in a very small space.
( I don't want to use a FET)..but its another option.
Do you know which is the "Best" of these you quoted
6S26B, 6S27B, 6S32B I guess there isn't a double triode same kind of voltage..
B+ will be around 250-270V.

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M. Gregg
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Old 1st August 2014, 04:29 PM   #4
mwiebe is offline mwiebe  United States
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Those tubes are very cheap so you better determine "best".
Since this is DIY and you want to create a physically small line stage why not just design circuit for the tube? Higher than necessary B+ makes any capacitor you use bigger than it needs to be. The volume of a 80V line stage can be much smaller than one designed for 270V, and the power supply is much smaller as well. If your power supply is non-negotiable you can always use a dropping resistor and decoupling cap to lower the plate voltage.

If you post the circuit with voltages you wish to use sub-mini tubes in that might help figure out what options work. Sub-mini's are small, two single triode tubes, especially of the flat bottle type, are not much larger than a twin triode in some cases.
Matt
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Old 1st August 2014, 05:28 PM   #5
M Gregg is offline M Gregg  United Kingdom
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Thinking about something like this..
Perhaps a 5718..put another 100k in series with the supply and reduce the B+..140-150V??
However I'm not familiar with the micro phonics and the types. ie the "Best" one..

http://frank.pocnet.net/sheets/079/5/5718.pdf

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M. Gregg
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Old 1st August 2014, 06:30 PM   #6
mwiebe is offline mwiebe  United States
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6N16B Twin-triode, 200V plate max, Mu 25, Rp 5K ohms
6BF7W Twin triode, 110V plate max, Mu 35, Rp 7K ohms
6S31B Single-triode, 100V plate max, Mu 17, Rp 950 ohms
5977 Single-triode, 180V plate max, Mu 16, Rp

I assume you need that input cap because you have DC on your signal, but I do not understand the large unbiased cathode resister as well as the large plate load for a 12AU7 type. I trust you have heard 12AU7s in this circuit and like what you hear.

You should be able to plug a pair of 5977s into that circuit and get something that sounds as good as a 12AU7 in there. Remember a pair 5977s have half the filament requirement of a 12AU7 so you might want to adjust to suit.

One 6N16B will sub in as well but its filament demands are more than a 12AU7 so you will need to pay attention to that issue and see what your filament supply does.

If you want a line stage for audio I would think going with the data sheet suggestions for operating points would be a better place to start. For example, 6N16B, 100V on the plate, 325 ohm cathode resister, 6.5mA plate current, and a 30K plate resistor suggesting a B+ of 280V. For 5977, 100V plate voltage, 270 ohm cathode resister, 10mA plate current and a 20K plate resistor B+ of 300V needed. You would only need to change two resisters to adapt, given your 250V B+.

A smart tuned circuit topology impacts sound more than any special tube. Good luck.
Matt
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Old 1st August 2014, 06:52 PM   #7
M Gregg is offline M Gregg  United Kingdom
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Thank's Matt,

I will have a look..

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M. Gregg
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Old 1st August 2014, 07:00 PM   #8
mwiebe is offline mwiebe  United States
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I just saw these,
10pc SUBMINIATURE8 B8D Tube Adapter Bare PCB for GE6021 6N16B 6N21B 2 0mm | eBay
They might be of use as you experiment. I also have wired sub-minis to 9-pin socket savers like this, I just solder them right to the socket.
10x 9pin Tube Socket Saver Fr 12AX7 12AU7 ECC82 ECC83 TS 9 | eBay

but this is only an advantage if you have a 9-pin socket that you want to try different sub-mini's in. If you solder in circuit your needs are different.
Matt
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Old 2nd August 2014, 02:39 AM   #9
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The 6111 is similar to the 12AU7 and can often be used in the same circuit with some resistor value tweaks. You must keep the dissipation down by reducing plate voltage, plate current or both. I have used the 6111 and the 6021 (higher gain) in a guitar preamp that fits inside the guitar. I run a B+ of 250 volts with about 125 volts on the plate. Current is about 5 mA if I remember right. These tubes will fit into a round 8 pin IC socket with a little pin bending and careful insertion...there is no keyway on the IC socket. They can be used in a machined pin 8 pin DIP IC socket with a lot of pin bending.
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Old 2nd August 2014, 05:02 AM   #10
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I've played with 6021, 6111, 6BF7's in a portable headphone amp running a whopping 12v and they sounded surprisingly good. Always wanted to try them with a proper voltage so watching this thread with interest..

For testing i plugged them into an 8pin dip socket as above, they dont make it easy to identify the pins so after you have squinted at them a few times trying to figure it out you will see the value of that approach.
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