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?
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.
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.
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.
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.
dsavitsk said:
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.
Re: Re: subminiature tube suggestion
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
This look promising, though the curves look pretty bad once the B+ gets below 50V or so.wa2ise said:
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.nuvistor said:
I think this is what I'm really looking for. Any part numbers?UncleNed said:
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
Re: Re: Re: subminiature tube suggestion
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.
dsavitsk said:
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.
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
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
Re: Re: Re: Re: subminiature tube suggestion
Sort of. Portable in the sense of taking it place to place, but not portable in the sense of battery powered. I designed a small wall powered DAC and I'd like to put it and a small head amp in a box. The size restriction is because I already have the box, so I am just investigating options. My only problem with the YAHA is that I have a rule (which is not always strictly enforced) against just building other people's designs. I like to at least have a hand in the process and try to figure things out, even if what I come up with more of less the same as what someone else came up with.nuvistor said:
Re: Re: Re: Re: Re: subminiature tube suggestion
Understood. I've been doing some LTSpice sims of a 2-stage amplifier with 6111 1st stage with CCS load, cap coupled into inverting feedback opamp 2nd stage, with NFB loop from opamp output to 6111 cathode, haven't built it yet though.
I looked at your DAC webpage, if you want to tap power from the DAC PCB you will need a bigger xfmr for filament power if using 6111 or 6922, directly heated filament submini triodes use much less filament power, some are listed on WA2ISE's website. You could use a voltage multiplier off your xfmr secondary to get some real B+, perhaps 40V.
A buffered opamp headamp like MINT could be incorporated much more easily of course, but there's no adventure in that.
dsavitsk said:
Understood. I've been doing some LTSpice sims of a 2-stage amplifier with 6111 1st stage with CCS load, cap coupled into inverting feedback opamp 2nd stage, with NFB loop from opamp output to 6111 cathode, haven't built it yet though.
I looked at your DAC webpage, if you want to tap power from the DAC PCB you will need a bigger xfmr for filament power if using 6111 or 6922, directly heated filament submini triodes use much less filament power, some are listed on WA2ISE's website. You could use a voltage multiplier off your xfmr secondary to get some real B+, perhaps 40V.
A buffered opamp headamp like MINT could be incorporated much more easily of course, but there's no adventure in that.
I probably will use a seperate transformer since the DAC's is so small.
Here is what I am thinking as a design -- it is similar to the millett design but uses a cap before the buffer so that an electrolytic on the output is not necessary, I 'm not really sure this will work at all though. The 6GM8 might be ideal, though I do think I'll either need a voltage reg between the B+ and the + power input to the buffer, or I'll need to run the tube even lower than I was thinking. The tube's heat dissipation is very low, so that isn't a problem, but maybe the voltage reg will be a problem ... did I mention that this is in a solid wood block just slightly larger than an RA-1 with no air holes? That's probably important information too.
As for the mint suggestion, I have been considering a single opamp amp based on the AD8397 which is good for power hungry headphones (grados.) Tangent is working on a successor to the mint using this chip as well, be he is unlikely to be done soon, so I'd like to get something working sooner than later.
Here is what I am thinking as a design -- it is similar to the millett design but uses a cap before the buffer so that an electrolytic on the output is not necessary, I 'm not really sure this will work at all though. The 6GM8 might be ideal, though I do think I'll either need a voltage reg between the B+ and the + power input to the buffer, or I'll need to run the tube even lower than I was thinking. The tube's heat dissipation is very low, so that isn't a problem, but maybe the voltage reg will be a problem ... did I mention that this is in a solid wood block just slightly larger than an RA-1 with no air holes? That's probably important information too.
As for the mint suggestion, I have been considering a single opamp amp based on the AD8397 which is good for power hungry headphones (grados.) Tangent is working on a successor to the mint using this chip as well, be he is unlikely to be done soon, so I'd like to get something working sooner than later.
Attachments
Your design should work. The cap can be a high quality type, I would choose a low dielectric absorption type like teflon, polypropylene or polystyrene film/foil. You will need a resistor to ground for BUF634 bias current. The 6GM8 appears to have about 2k plate resistance so driving the BUF634 and using a simple PNP/LED CCS should work fine.
A tube with 6.3V 300mA heaters will dissipate about 2W, a 6GM8 with Vp=25V and Ip=10mA will dissipate 2.5W. You should provide some ventilation, more for the SS than for the tube.
If you need something right now I'd just use op amp du jour with BUF634 ala MINT, low parts count and probably compatible with your DAC supply, with a bipolar supply you don't need the rail splitter, you probably have all the parts to build. AD8397 is high GBW, you should have access to a oscilloscope 60MHz or faster to check for oscillation.
At some point you might consider using the AD8397 with inverting feedback instead of the BUF634, driven by the mu output of a Pimm CCS, but this is more complicated.
A tube with 6.3V 300mA heaters will dissipate about 2W, a 6GM8 with Vp=25V and Ip=10mA will dissipate 2.5W. You should provide some ventilation, more for the SS than for the tube.
If you need something right now I'd just use op amp du jour with BUF634 ala MINT, low parts count and probably compatible with your DAC supply, with a bipolar supply you don't need the rail splitter, you probably have all the parts to build. AD8397 is high GBW, you should have access to a oscilloscope 60MHz or faster to check for oscillation.
At some point you might consider using the AD8397 with inverting feedback instead of the BUF634, driven by the mu output of a Pimm CCS, but this is more complicated.
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