Tube buffer has it been done a lot & how to?

[albatross]

After looking at opamp buffers and jfet buffers here http://www.muzique.com/lab/buffers.htm
, i was wondering if tube buffers are used a lot?

Would you just take a jfet buffer design, wire up one side of the tube and maybe if (needed) use the other side as a output buffer?
supply voltage to pins 4.5, most importantly would this work, and would it run at 9volts?

Also would a bridge rectifier and 9v voltage regulator be needed if  you feed it 12Vac or dc to regulate to 9vdc?

Im just curious if this is used and how it could be done for low voltage, and whether it would make a difference or not, I tried searching without any success.

[The Tone God]

i was wondering if tube buffers are used a lot?

Not really. Costs and environmental issue come into play. You need larger power supplies, more circuitry, large components, and deal with things like heat and safety. For these and other reasons there is not much interest in or even need for tube buffers hence why you don't see them often.

...whether it would make a difference or not, I tried searching without any success.

This is of course a matter of opinion but besides the issues listed above you won't get much better performance from a low voltage tube buffer unless you want to heat your feet.

Not that it can't or shouldn't be done but unless you have specific requirements there are much easier ways to make a buffer.

Andrew

[albatross]

Thanks for taking the time to reply, I was just curious if anyone has bothered to try, it would be interesting and different if it works
definately not something you come across often

[The Tone God]

Interesting, perhaps. Different, well different how ? Tonally you may be disappointed as after all that work you may find no special audio characteristics become apparent with low voltage tubes. So I am hinting if that is the case, which I believe it is IMHO, why not just use solid state to begin with ?

I haven't heard of stand alone low voltage tube buffer but I think VHT (?) has a pedal power supply with a high voltage tube buffer built in.

If you want to make one just for a laugh then by all means go for it.

Andrew

[tiges_ tendres]

The company VHT makes a tube buffer.  It also doubles as a power supply for other pedals, and also a groud lift.

(EDIT) I now see that this fact has been posted directly above me!

[albatross]

Hi,

Got the jfet buffer on the breadboard, works fine
Now, i have a tube rigged up with all wires on the socket, am I right in thinking even with 9v the tube should still glow?

As mine isnt!

I have put pin 4 to +9V and pin 5 to ground, no luck. but im only using 1 side of the tube

[alextheian-alex]

I've done it... several time actually, at voltages ranging from 6-350v.  A few tubes in current production that will work well down in that range are 6DJ8/6922 and 12au7/ecc82... even a 12at7/ecc81 CAN work, but steer clear of 12ax7/ecc83 at those voltages.... it just gets bad.

 You are going to be well below where the tube can be in any way linear, but we don't mind that in guitar land.  Harmonic distortion is very very high even with no clipping at all, but it will be mostly even order, so it actually ends up sounding very round and warm... if that is what you are going for.  If you want a flat response... well that is a bit harder.  a 6922 can get you there with a bit of local feedback, but I would not bother with that idea since it will end up resembling a S.S. stage anyway.  i did it just for kicks, and the results were just ... meh.

[brad]

http://www.diystompboxes.com/smfforum/index.php?topic=55453.0

Uh...folks ^^

[alextheian-alex]

Hi,

Got the jfet buffer on the breadboard, works fine
Now, i have a tube rigged up with all wires on the socket, am I right in thinking even with 9v the tube should still glow?

As mine isnt!

I have put pin 4 to +9V and pin 5 to ground, no luck. but im only using 1 side of the tube

Do you have power running to the filament?  If not you need to.

[albatross]

yes, I have pin 4 to +9Volts and Pin 5 on a 12ax7 which i have at hand to ground, shouldnt this be enough just to see it light?
or do all connections have to be used for the tube to light?

what i mean to say is , why isnt it lighting? do you need 12v or 6 volts etc for it to light?

PS:That looks good brad! will try it oneday when I get the parts together

[alextheian-alex]

yes, I have pin 4 to +9Volts and Pin 5 on a 12ax7 which i have at hand to ground, shouldnt this be enough just to see it light?
or do all connections have to be used for the tube to light?

what i mean to say is , why isnt it lighting? do you need 12v or 6 volts etc for it to light?

PS:That looks good brad! will try it oneday when I get the parts together

That should do it.  I am holding one in my hand right now that is set up the same way.  The glow wil be very very faint, but it should be there.

[brad]

yes, I have pin 4 to +9Volts and Pin 5 on a 12ax7 which i have at hand to ground, shouldnt this be enough just to see it light?
or do all connections have to be used for the tube to light?

what i mean to say is , why isnt it lighting? do you need 12v or 6 volts etc for it to light?

PS:That looks good brad! will try it oneday when I get the parts together

Don't bother with the 12AX7.  The 12AJ7 was designed especially for 12v, costs $2 on eBay, and was made in the golden days of tube manufacturing.

[albatross]

I am trying to power mine from a 9v battery, tried a fresh battery and still no luck, whats strange is , when i apply + to pin 4 and - to pin 5 i dont get any voltage reading on my dmm on pin 4 when i should obviously get 9v.

I tried a fresh tube also, definately not lighting up.

So you definately need 12V?

[albatross]

I have now since tried with a clear untired head, 9v dc supply rigged up, didnt realise the guitar volume was rolled right down, i see a tiny bit of glow now

Tried also with 12vac, glow was brighter and slightly louder.

Sounds misbiased, very farty sounding

I have it setup like this:

Replacing the jfet:

Drain with Anode1
Gate with Grid1
Source with Cathode1

If i unplug the Anode1 it still works, but if i unplug the Cathode1 or Grid1 it dosent, is this becuase the jfet receives power through the drain, but now the tube receives power through the actual heaters so the drain/anode1 dosent function correctly?

[albatross]

Right, Now I have gotten it working a lot better sort of

I borrowed some of brads values, and it is working but still a bit unbiased, but almost there
From what I can tell the tone sounds smoother, unless im imagining it!

To test, I unplugged power and you can tell it is the tube doing the stuff as it warms up, is spattery for a few secs then goes almost normal.

I put together a quick schematic of how it is so far with 9V DC and a 12xa7.



R1 = 68K
R2 = 1M
R3 = 220K
C1 = 1UF
PIN 9 of the tube to ground also!

heres a soundclip directly into the pc:

http://www.rogepost.com/n/1273626298

i'm trying to emphasise the distortion farty sound which seems to be more present in the bass strings, ignore the playing

You can tell it wants to work, any suggestions on how to improve?, anyone want to try for themselves on a breadboard?

The tube also keeping my hands warm as its cold.


EDIT: Since i have tried a 470K trimpot at R1 and R3 and fiddling with them dont do much, at r1 position it can act as a volume control.

changing the cap dosent do much neither, adding a 1M resistor at the output does nothing, so maybe I was imagining things.

[alextheian-alex]

Try to get ahold of a 12au7 or 12at7... they will be much less farty at thse voltages.  You could also try a space charge tube like Brad did, but you can't pick one up at the local Guitar Center.

[albatross]

Thanks alex and everyone for the helpful suggestions

I am gonna order some soon from ebay of both types when i can afford them, moneys short at the minute

It was interesting to mess about with this as ive only ever built a tubepedal before, I know tubes can be adjusted to work a bit as diodes, transitors etc so Im gonna try this out on other things, but i doubt these could be run on batterys without instantly draining them

Im gonna try brads method when i get the tubes required.

As im relativley new to tubes, I found that when you use 9vdc, pin 9 has to goto ground, but - is not grounded, instead - goes stright to powerjack - (not grounded) otherwise the tube wont light, that caused some confusion, as at first i thought like normal effects, where - goes to ground...

Think ill start another pedal on the breadboard now, Im thinking of a opamp , with clipping diodes replaced with a tube, been done yes, but audio electronics is fun!

[g.]

really simple 6AK5/EF95 buffer



from this site :
http://www.mhsoft.nl/MySystem/HiFi.asp

[GibsonGM]

I'm getting into the tube thing, too, albatross.  One thing other than personal safety to watch for if you go up in voltage (which I recommend for better results) is your parts ratings...according to my math the 50R's in the above schem should be at least 1/2W or you'll probably fry the resistors.  The 10K after the rectifier should be 2W, and the bridge should handle >2W power dissipation.

You need a dual power supply, and it's the heaters that draw all the current!  .6A for a 12AX7.  This is why solid state buffers et. al. were revolutionary...the tube sound on a buffer probably won't be amazing.   But good way to learn more about tube circuits, for sure!