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Old 21st December 2005, 09:06 PM   #1
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Question subminiature tube suggestion

I am looking for a physically very small tube (dual tride would be ideal, but single triode is fine too, or a pentode that can be used as a triode) that provides medium to low gain, can run on a low voltage (~24-30V range), and that sounds decent. I'm am aiming to use it with a plate load CCS for voltage gain coupled with something like a buf634 for output -- much like Pete Millett's low voltage headphone amp. Does anything like this exist?
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Old 21st December 2005, 09:54 PM   #2
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Default How about a Nuvistor?

There are some very low voltage (12V) type Nuvistors around, and even the common medium gain types like the 7586 can work as low as 40V
The downside is they can sometimes be michrophonic........
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Old 21st December 2005, 10:27 PM   #3
wa2ise is offline wa2ise  United States
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The 6111 is a twin triode medium mu tube that I've run as low as 40V.
This circuit uses it as a cathode follower, but it should work in other configurations. More at my page
http://pw2.netcom.com/~wa2ise/radios/tubedac.htm
and look for the section on players with TDA1543 DAC chips.

You might be able to acquire higher B+ voltage with some voltage doubler circuits. Also you can get higher voltages across the tube itself if you have negative supply voltages avaliable.
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Old 21st December 2005, 10:39 PM   #4
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Check out headwize.com DIY Workshop, there's several variants on your theme including versions in your voltage range:

YAHA

MHHA

iHybrid Nano

6111 has been used in these with B+ of 12V or so. 6922/ECC88/6DJ8 is also used at 24V. I haven't built one so don't know what it sounds like, probably has a lot of 2nd HD which would conflict with my high NFB tendencies.
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Old 21st December 2005, 11:02 PM   #5
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Default Re: subminiature tube suggestion

Quote:
Originally posted by dsavitsk
I am looking for a physically very small tube (dual tride would be ideal, but single triode is fine too, or a pentode that can be used as a triode) that provides medium to low gain, can run on a low voltage (~24-30V range), and that sounds decent.
There are series of tubes meant for use with 12 volt auto radio
batteries, like 12EA6 tinyurl.com/8x9rh
and 12U7 tinyurl.com/c5dkb
and subminiature ones made for battery-powered hearing aids and walkie-talkies (don't recall numbers off the top of my head). Most of them aren't terribly common but not terribly expensive due to the low demand.

As someone else noted, it's possible to run regular tubes at fairly low plate voltages, heck, you could probably use antique-radio battery types like '01A or '30 if you like, although the microphonics might be higher than you like.

While all these do work, the maximum signal voltage output you can expect to get is somewhat limited by the low B+ voltage.
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Old 21st December 2005, 11:44 PM   #6
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Default Re: Re: subminiature tube suggestion

Quote:
Originally posted by wa2ise
The 6111 is a twin triode medium mu tube that I've run as low as 40V.
This look promising, though the curves look pretty bad once the B+ gets below 50V or so.

Quote:
Originally posted by nuvistor
Check out headwize.com DIY Workshop, there's several variants on your theme including versions in your voltage range:
I am familiar with those. I am looking for something to cram into a very small space (5" x 2" x 1" for both amp and PS), so even the 12ae6a is probably out. This is likely a losing battle, but I thought I'd investigate. It may be a place for solid state, though.


Quote:
Originally posted by UncleNed
and subminiature ones made for battery-powered hearing aids and walkie-talkies (don't recall numbers off the top of my head).
I think this is what I'm really looking for. Any part numbers?

As a side note UncleNed, I just moved back to Chicago, and I am sad youare not associated with Triode anymore. Are you planing to do another brick and mortar?

-d
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Old 22nd December 2005, 12:20 AM   #7
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Default Re: Re: Re: subminiature tube suggestion

Quote:
Originally posted by dsavitsk

I am looking for something to cram into a very small space (5" x 2" x 1" for both amp and PS
iHybrid Nano and YAHA fit everything except batteries in an Altoids tin, you probably could add 10 AAA NiMH batteries and an NiMH charge controller and fit your size or slightly larger. You don't describe your application but I assume this is for a portable headphone amp.
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Old 22nd December 2005, 12:25 AM   #8
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Quote:
As a side note UncleNed, I just moved back to Chicago, and I am sad youare not associated with Triode anymore. Are you planing to do another brick and mortar?
Doh,Really?
Guess I missed that memo.
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Old 22nd December 2005, 01:17 AM   #9
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Quote:
Originally posted by DigitalJunkie


Doh,Really?
Guess I missed that memo.
I swear I saw a thread about this, so hopefully I'm not spreading rumors ...
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Old 22nd December 2005, 01:30 AM   #10
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Dsavitsk,

Could you "live" with 1 small 9 pin mini bottle? If so, the 6GM8 seems IDEAL for your needs.

BTW, you're not spreading rumors. Ned's New Home in CyberSpace
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