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Old 9th October 2007, 05:59 PM   #1
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Default Looking for low-ish rp single triode

I am looking for a tube to use in a preamp. I need a single triode, or pentode that can be triode strapped, has a mu in the area of 15 to 25, and has an rp of 2K5 or lower. Octal or loctal is ideal, but 9 pin will work, and if possible, a 12V heater is preferred.

I have already used 6688's and 7788's, so I don't want to use them again. 5842's and 7737's are a little too expensive, 12j5's and their variants have too high of an rp. 6t4 is a 7 pin but otherwise promising. C3m looks almost ideal except for the price and lack of availability. Really, I am looking for 1/2 of a 5687 if it exists.

Any other suggestions?
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Old 9th October 2007, 07:13 PM   #2
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a 5687 paralleled? rp of 1000 or so
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Old 9th October 2007, 08:27 PM   #3
JimW is offline JimW  United States
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ECC99 has rp of 2700, mu of 22, and 6.3 or 12.6 heater. Both section could be ran parallel for even lower rp.
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Old 10th October 2007, 09:06 PM   #4
KaDe is offline KaDe  Germany
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If you are bored with your locals, here is a nice single triode matching your request: LD15
Rp=2k, but it looks more like a collector item.........
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Old 11th October 2007, 12:21 AM   #5
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Borderline between big signal tubes and little power tubes...

Maybe triode-connected 6CL6, or 12EH5/12CA5? Cheap and worth a try...

I know there are also similar tubes in loktal bases, just don't know the numbers offhand. Try cruising through the "14xx" tubes in the Sylvania manual:

http://www.pmillett.com/sylvania_tub...als_online.htm

you might see something good.

Pete
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Old 11th October 2007, 02:21 AM   #6
siang is offline siang  Taiwan
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How about a russian tube? 6s3p-E. If you can, get the one with the "E" marking.
But I would highly recommend c3m, you can get them easily.

siang
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Old 11th October 2007, 03:49 AM   #7
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Quote:
Originally posted by sorenj07
a 5687 paralleled? rp of 1000 or so

Quote:
Originally posted by JimW
ECC99 has rp of 2700, mu of 22, and 6.3 or 12.6 heater. Both section could be ran parallel for even lower rp.
I'm trying to avoid parallel sections, if for no other reasons because it feels like cheating, and I'm not sure I have the heater current.


Quote:
Originally posted by KaDe
If you are bored with your locals, here is a nice single triode matching your request: LD15
Rp=2k, but it looks more like a collector item.........
If I could only find some. neat tube.


Quote:
Originally posted by pmillett
Borderline between big signal tubes and little power tubes...

Maybe triode-connected 6CL6, or 12EH5/12CA5? Cheap and worth a try...
Thanks Pete. The only real issue is that there are already octal holes cut, and while I have some octal to 9 pin hole shrinkers, I have never seen either octal to 7 pin, or a 7 pin socket that is as large as a 9 pin. I'll look around though as it seems like a good option.

I'll look for a loctal too.


Quote:
Originally posted by siang
How about a russian tube? 6s3p-E. If you can, get the one with the "E" marking.
mu seems a little high, but it seems like a useful tube for other things.
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Old 11th October 2007, 06:49 AM   #8
cerrem is offline cerrem  United States
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Keep in mind that for what you are asking, there will be trade off's.....such as a hefty bit a DC idle current for your requirements,,, None the less....to answer your request, take a 6V6 in TRIODE mode...Rp is about 2.4K and the mu is about 10....and it is an octal base....
Either tie the L and R stereo 6.3V heaters in series for 12.6V or use the 12V6 .....
Should get the job done....

Chris
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Old 11th October 2007, 07:51 AM   #9
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Quote:
Originally posted by cerrem
Keep in mind that for what you are asking, there will be trade off's.....such as a hefty bit a DC idle current for your requirements,,, None the less....to answer your request, take a 6V6 in TRIODE mode...Rp is about 2.4K and the mu is about 10....and it is an octal base....
Either tie the L and R stereo 6.3V heaters in series for 12.6V or use the 12V6 .....
Should get the job done....

Chris

That's a good idea. I was thinking EL84 variants -- 10BQ5, etc. or maybe even a 12W6GT? I've used 6W6GT's before and these are a real sleeper -- good sound for no money at all.
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Old 11th October 2007, 10:15 AM   #10
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I'm going to take some liberties with your request, and recommend the 5676. This is cheaply available and mu of 15 but different in all other respects. Miniature directly heated triode with four wires coming out the bottom. So various ways of attaching. I solder to a tag strip. Must be used vertical, and must have a good DC supply to each tube, though this is low current. Batteries are another possibility. It's not particularly microphonic.

What you will get is crystal clear sound - it's in my current favourite preamp, working parafeed. This tube came close to winning the European Triode Festival prize for phono stages in one design.

http://www.rintelen.ch/hifi/lil_sis.pdf

You could be very surprised!
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