From perusal of my posts, I probably have no business attempting to design a headamp, much less a tube hybrid. But do know my way around electronics & schematics & datasheets to some degree. And I do have some time some nights & do like to stick to things until complete. Now to the point...

I'll be receiving a nice Vincent SA-31 preamp any day now & their products often feature the cute, tiny (10mm dia, 36mm long?) Russian 6N16 audio.ring.lt/pdf/6n16b.pdf. They are from the pinnacle of Russian tube development & although designed for military apps reportedly sound very nice in some applications. I have a small NOS lot of them coming my way (2 in case my SA-31 needs 'em, the rest for fun).

Thinking I *may* like to try my hand at designing a very small portable (AC powered tho) headamp based on these someday... Perhaps borrowing heavily from http://audio.ring.lt/pre/pre_en.html and original SOHA design. Tube rolling would be out, but opamp rolling would not.

Guess I'm curious if this would a silly endeavor & if not, would anyone be interested/have any thoughts/advice.

I've not researched this. (edit: An ebay seller has 2 NOS 100 piece lots of these & seems to have em fairly often... Also there are other pencil tubes - pinout/availability/SQ TBD). But after reading my own audio.ring.lt/pre/pre_en.html link completely, searched for terms "pencil tube" & amplifier...

Turns out there are some related projects around (have yet to read these too); home.hetnet.nl/~a.van.waarde/id17.htm, www.headphoneam...ijosae/Gallery/ and www.geocities.c...dio_pre_amp.htm.

> I would like to see this project developed.

Me too since I have to own 2 SOHAs (1 for work, 1 for home) & think a more transportable may be of use.
And sometimes, if one wants something done they may have to do it themselves

BTW, not that anyone would, but don't be put off by the 750hrs guarantee in the datasheet - Thinking that's an overly conservative replacement suggestion for military apps.... Guessing these tubes would go 1000s of hrs.

[Edited by cfcubed on 07-23-2008 at 11:03 AM.]

Great resource this HeadWize forum I'll read the related info & maybe try to interact w/some from the cast of characters on that project...

[Edited by cfcubed on 07-23-2008 at 12:42 PM.]

[Edited by dBel84 on 07-23-2008 at 02:23 PM.]

The tube is like an improved 12AU7, and needs more power (especially heater) than 12AU7.

So while the actual amp may be "cute", the power supply is as big as any other, and will dominate overall cuteness.

The small size of transistor gear is not about transistors being smaller. It is fact that a tranny will give usable gain at much less B+ consumption and zero heater consumption, allowing much-much smaller power supplies.

Not that it is a bad idea. Just that a small tube does not ensure small equipment.

Is this to drive the phones? 12mA is not a lot of oomph, unless you can find a 10K:50R output transformer. Which may be bigger than the tube.

> Are there any new 6N16 tubes being made?

Don't need any. The USSR, even more than the US, kept specific tube lines running for military-spares purposes well into the 1980s, even after the warehouse was full and demand had slacked off. Sometimes there was a "reason". Submini tubes were used in top-secret proximity fuses. The existence of such things was secret, so nobody could reveal that they had been discontinued. And as in any vast organization, the left hand never tells the right hand what is going on. And military contracts pay well, so the tube maker is encouraged to over-produce.

In this case, I have a sneaky suspicion that the USSR sold their used tube machinery to China and it is still running.

---

[Quoting PRR]

> the cute, tiny (10mm dia, 36mm long?) Russian 6N16

The tube is like an improved 12AU7, and needs more power (especially heater) than 12AU7.

So while the actual amp may be "cute", the power supply is as big as any other, and will dominate overall cuteness.

---

Yes, more research shows devices using it aren't so svelte:
www.audioadviso...number=SLPH3000
www.pacificvalve.us/BPH1.html

Thank you for the replies... As from the OP, I was looking for a reality check & its coming around. Yes, as dBel84 indicated this being a "real tube" made me look closer at its DS & see its PS requirements.

For this project to make sense it would have to address a niche or gap in current available projects. I was thinking it could be a transportable w/respectable performance.

We'll see if the dozen extra NOS 6N16Bs pressure me into attempting this exercise anyway Though going w/another "pencil tube" would likely be the way to go....

[Edited by cfcubed on 07-24-2008 at 07:28 AM.]

I foresee an irresistible urge to tinker with the spare doz tubes in your near future ..dB

---

[Quoting dBel84]

I thought I had seen this particular tube used before. Here it is in the Little Dot Micro Tube < snip >
[/b]

---

And my what a BIG power supply it has www.head-fi.org...e-house-212528/

I foresee an irresistible urge to tinker with the spare doz tubes in your near future ..dB

And I was hoping it was not that www.diyaudio.co...threadid=105526 obvious img409.imagesha...6334/bd3pn0.jpg

[Edited by cfcubed on 07-24-2008 at 03:19 PM.]

Truly portable all-tube audio exists.

http://www.porta...bles/mycoll.htm
http://www.geoci...1JapanTube.html

While these are mono radios, a stereo amp would be around the same size.

This is cute (9"x6"x2" approx.), despite those fatso tubes:

OTOH, this Lear has a handle....
http://www.porta.../learavian2.htm

[Edited by PRR on 07-24-2008 at 08:47 PM.]

---

[Quoting tedro]

I have a couple of 6021, 6111 and 6112 sub miniature tubes that I would like to use.

---

I guess you saw the YAHA above headwize.com/ub...=65257&fpage=25 not sure of its performance tho...

Anyway, all those 6N16Bs' beady little eyes will likely wear me down to doing something with them. From poking around & not wanting to "wing it", I ordered Mr. Jones' Valve Amplifiers book... Since "Beginner's Guide to Tube Audio Design" is out of print & it looks like for my particular needs, VA is a better fit.

So I might be on sabbatical on this for a long while, but y'all may be hearing from me about this someday

For this project to interest me, it has to meet these requirements:
1) transportable, single case design... No bigger than Hammond (1455K1202BK) 4.72 x 3.07 x 1.69. Want something that fits easy in a briefcase, etc.
2) SQ equal to or better than the orig SOHA. So far I feel the SQ of this POC is better than my SOHAs.
3) Muting delay

And its looking so far that those requirements can be met.

SOHA base changes:
1) 12-0-12 transformer (using +/- 12v) because
2) using SOHA II 2.5x multipler - 94v under load (want to stick w/100v caps)
3) running 6N16B at same plate current as SOHA (1.1 ma) but plate voltage @ 70v. To me this looks to fall on the tube's -2V ave plate line & 1.1ma plate current point.
4) LM337 / R11 = 5.1k giving 6.3v heater.. The only issue now is that puppy gets a bit toasty. May use 7906 here & plan to use case as HS (w/insulating pad/screw) if this goes that far.

Quick & dirty schematic & PCB layout (traces were there but too embarrassing to show indicate that the necessary components can be jammed into the desired case. BUT that could cause its own issues/problems of course. Note: some changes have been made since these drafts:

( early schematic & PCB layouts pulled pending revisions )

(one of my 1st tries @ PCB layout & it shows Plan for all diodes & resistors installed on end (or use 1/8 watt mini resistors which could lay flat).

Anyway, going to box up the POC in the orig SOHA case, live & listen to this baby for a while and if all goes well might go further with it.
BTW, supply of NOS 6N16Bs looks like no problem - the ebay seller I bought my 20 from says he has 1500+ of them.

Credit for most of this goes to SOHA & SOHA II developer & designers of course (Thanks!). Hoping y'all are o.k. with using bits of SOHA & SOHA II design for this

[Edited by cfcubed on 10-06-2008 at 08:37 AM.]

That multiplier really delivers 94V? I have to think some more.

> LM337 ... 6.3v heater.. The only issue now is that puppy gets a bit toasty. May use 7906

As dBel says: same drop, same current, same heat. Oh, one or the other may run 1mW cooler due to different internal losses, but you are dropping 13V to 6V at 0.4A, that 2.8 Watts is your toaster.

Considering "fits easy in a briefcase" and "puppy gets a bit toasty", I would suggest radical re-simplification of the power supply. I'm not sure which way to jump, though, with need for 6V, two 15V, and a 90V. It begs a 3-winding transformer.

The op-amp does not NEED regulated power. (Its supply rejection is much better than the tube, and you didn't regulate that.)

The tube does not need regulation; and with with twisted-pair (not PCB) wiring, you could get away with balanced AC heat.

In this 21st century, it ought to be trivial to kick-up 100V from low voltage with a silicon "buzz-coil"; but there is no large market and thus no standard part.

It would be much cooler to use a switcher to drop ~~13V to 6.3V; and this just may be a small-mod on a standard part. (I have a junker board which takes 12V and makes 5V and 3.3V at good current with negligible heat.)

You could look at 6V and USB microphone amplifiers with Phantom Power. This is 48V at 2mA-16mA. It is very common to use a 555 or a CMOS buffer array running just above the audio band, and a multiplier stack using quite small (0.1uFd) caps.

You sure the transformer has to be that large? Your actual load (not counting regulation losses) is 2.5W in heater, <0.4W in opamp, 0.22W in plate circuit. Just over 3W. Most of this is in heater regulation which is running <50% efficiency. So 6W demand (3W heat), conservatively double to get VA, 12VA, 10VA may do. OK, your 15VA part is not excessive (the 25VA does seem over-generous for briefcase). But a more efficient power plan leads toward 7VA iron, slightly smaller and much lighter.

Toroids stack nice. This gets Voltages in the three zones without regulation parts and loss:
heater: 62010 2x7V 229mA 42.0x7.0x17.5 89 grams
opamp: 62002 2x12V 67mA 37.5x7.0x17.0 71 grams
Plates: 62005 2x22V 36ma 37.5x7.0x17.0 71 grams

It comes to an ounce less than your 62053, 5/8" less diameter, though a bit taller.

The 2X22V or 44VAC will give 61VDC directly on one cap; 2x18VAC to a doubler will give 102V and two 50V caps will probably live forever.

>SMDs - Don't like to work with the really tiny bits myself & perhaps using some of PRRs suggestions would yield PCB space.

>7906 / heat - Was planning to use a 3 watt power resistor before it (ala R3P in new SOHA II schematic).

PRR
Great, thorough suggestions & explanations as always! And if I were really a designer, instead of someone 1/2way through Basic Building Blocks of VA, it could be possible for me to actually innovate & integrate the suggestions into something new & better

Having built my 1st SOHA from Jeff's kit then a bit more complex FW F1/F2 build: www.diyaudio.co...threadid=128456, attempting to integrate/tweak existing designs was my next step.

Real innovation would take much more time (learning / benching) & likely $$s buying the various parts to try out (toroids, inevitable blown-up parts replacements). Not sure I'm up for that yet

> plate resistors? - Yes, schem is not complete - stuff was awaiting playing around w/this bench/POC.

> That multiplier really delivers 94V? - Yes, under load w/12-0-12 & tube @ 70v / 1.1ma. 15-0-15 was up around 118v under same conditions. The caps / CCS comps I planned to use are only good to 100v. May try running the tube at 2ma or 3ma for kicks in this POC to note any SQ changes & that might alter things.

> I would suggest radical re-simplification of the power supply. I'm not sure which way to jump, though, with need for 6V, two 15V, and a 90V. It begs a 3-winding transformer.

I guess, but sourcing such a transformer is hard & wanted singe-transformer design using readily available part (actually, one from my transformer box was strongly preferred

> The op-amp does not NEED regulated power. (Its supply rejection is much better than the tube, and you didn't regulate that.) The tube does not need regulation; and with with twisted-pair (not PCB) wiring, you could get away with balanced AC heat.

The suggestions above I understand & would help w/reduced part count, heat, ec.

Whereas these hold mystery for me:
> It would be much cooler to use a switcher to drop
> Phantom Power

> You sure the transformer has to be that large? .... slightly smaller and much lighter. - The measured total draw is between 400 - 450ma, so yes a smaller 12-0-12 (700ma total?) would work for this as is.

> Toroids stack nice. This gets Voltages in the three zones without regulation parts and loss:

Thanks for this (I do have a nice small 2x22 around), but available case sizes are dictating some choices here as is total cost of a build.

Thanks again, all great points & after listening to the POC for a week or two, if still really liking it I'll have to look closer at trying out some of the suggestions.

I made a neat little project a couple months ago and it sounds pretty decent. Uses the 6088 sub mini tube and a class a output. I am going to build another with BJT/LM317 output stage. It has good detail, not too bassy. I call it the BIC (Because I Can) just that it uses a 6088 first stage( no where close to audiophile grade) but I really do not push them too hard. Uses an 18 - 22 volt ITE power supply. All in all a fun little amp.

[Edited by roggom on 09-29-2008 at 09:57 AM.]

Re: multiple transformers/heat/weight - After getting cozy w/Mouser catalog & hitting Digikey couldn't find anyway to get > 1 transformer into an easily transportable inexpensive alum case (w/o resorting to EL/split bobbins). So in a week or so, hoping the LM337 holds out, I'll dig more into the issue of heat(er) supply (& pinning down CCS, etc.). Will look at splitting heat (5W resistor -> reg.) & maybe switchers (depending on assoc component count, etc.).

Now back to the music... Thanks again!

---

[Quoting roggom]

I have been following this thread, just wondering which program did you use for the schematic? I have seen it as tangent uses it, but i have only used TINA.

---

I'm using the free ExpressPCB tools right now... Made up 1st PCB order from them for my F2 amp boards & went well for me.
I need to consider getting into circuit sim progs (e.g. OrCAD or Pspice from what I read).

Your project looks neat... I haven't looked over other pencil tube specs e.g.amps.zugster.net/projects/subminiature, but they are cute & I think were designed toward the end of tube goodness for the military, so they should be tough & have pretty good specs when run at decent operating points.

As before, I am really enjoying the sound of my POC, so the potential is there if one is willing to give up tube rolling I guess. From the little I've poked around think it wouldn't be too difficult to morph things a bit to support other pencil tubes.

Fun stuff!

http://www.ttvj...cfcb0a2752fcc29

The amp received great reviews at the 07 Stereophile Head-Fest http://www.ster...news/407headfi/

I tried various ways of battery power and had minor success with a maxim DC-DC but the my circuit has no noise rejection, so the maxim noise bled into the amp. I am happy with the 22v wallwart power.

[Edited by roggom on 09-29-2008 at 12:19 PM.]