michael bateman wrote:

I'm looking to build a battery-powered tube preamp for guitar, and I came
across this schematic:

http://guitarrage.virtualave.net/eff...istortion.html

I'm no tube amp expert, but this seems weird to me. All of the other 12AX7
designs I'm familliar with have high voltage (150 - 450V) on pins 1 and 6
and grounded through 3 and 8.

The schematic I linked to connects pin 1/6 to ground and pin 3/8 to -15 V,
and has no high voltage indicated. I know enough to say that the electron
flow through the tube should be the same for this design as the other, since
pin 1 is still positive compared to pin 3, but I'm at a loss to figure out
how this circuit works without a high voltage source. I mean if 15 volts
will give a working (and decent sounding) circuit, why does every other
design I've come across use such high voltages?

Any feedback appreciated: Especially any links or info that might help in
building a battery-powered tube preamp.

An awful lot of tube pedals and even preamps run a 12AX7 at low voltages. Same goes for
"hybrid" style amps that turn out to be nothing but a SS preamp with tube a low voltage for
distortion voicing.

As others indicated, it's quite ok.
I'm in the process of trying out circuits for a battery powered
tube guitar amp. Unless one want to lug around 12V 30Ah + batteries,
the lookout is for low power consumption tubes, heck, maybe an
opamp or 2 (like BB OPA2604 at +-22V for tone controls).
Subminiature tubes safe a bundle on filament power requirements
and naturally run from low plate voltages. Just got me a batch of
CK5672 at 1 $ each, 1.20V@44 mA = 53 mW filament power.
These 'oversized chewing gums' are fine linestage tubes, running
at Vak=74 V 2mA, Ra= 39 K easily doing 60 Vtt out (Av=4) triode connected.
Should last awhile, as they are cold to the touch, actually heating up
from my thumb

A set of CK6612 's in triode mode might replace the 12AX7's, the filament
will give a -1.25V bias and can be fed from a 6.3V supply (or lower)
through a resistor.
Not gotten hold of these yet, sure seems worth experimenting with.
In a distortion pedal, it could then be powered from a bunch of NiMH cells.
Just a thought,
Cheers,
Rudy

"michael bateman" wrote in message
.. .
: I'm looking to build a battery-powered tube preamp for guitar, and I came
: across this schematic:
:
:
http://guitarrage.virtualave.net/eff...on/eti83_tube_
distortion.html
:
: I'm no tube amp expert, but this seems weird to me. All of the other
12AX7
: designs I'm familliar with have high voltage (150 - 450V) on pins 1 and 6
: and grounded through 3 and 8.
:
: The schematic I linked to connects pin 1/6 to ground and pin 3/8 to -15 V,
: and has no high voltage indicated. I know enough to say that the electron
: flow through the tube should be the same for this design as the other,
since
: pin 1 is still positive compared to pin 3, but I'm at a loss to figure out
: how this circuit works without a high voltage source. I mean if 15 volts
: will give a working (and decent sounding) circuit, why does every other
: design I've come across use such high voltages?
:
: Any feedback appreciated: Especially any links or info that might help in
: building a battery-powered tube preamp.
:
:
:

michael bateman wrote:
I'm looking to build a battery-powered tube preamp for guitar, and I came
across this schematic:

http://guitarrage.virtualave.net/eff...istortion.html

I'm no tube amp expert, but this seems weird to me. All of the other 12AX7
designs I'm familliar with have high voltage (150 - 450V) on pins 1 and 6
and grounded through 3 and 8.

The schematic I linked to connects pin 1/6 to ground and pin 3/8 to -15 V,
and has no high voltage indicated. I know enough to say that the electron
flow through the tube should be the same for this design as the other, since
pin 1 is still positive compared to pin 3, but I'm at a loss to figure out
how this circuit works without a high voltage source. I mean if 15 volts
will give a working (and decent sounding) circuit, why does every other
design I've come across use such high voltages?

Any feedback appreciated: Especially any links or info that might help in
building a battery-powered tube preamp.

This circuit is essentially a pair of cathode followers, so it will have
a gain less than unity (probably considerably less than unity, since the
gain of the 12AX7 will be quite low at such a modest B+ voltage). What's
more, the grids are biased positive with respect to the cathodes. The
net effect is a considerable amount of non-linearity. This non-linearity
will be approximately equal on positive and negative excursions, so the
clipping will be approximately symmetrical (which means that the
distortion products will be mostly even-order harmonics).

The drawing is unusual, that might be one of the things confusing you.
However, the way it's drawn (and the fact that it uses a positive
ground) does emphasize that the circuit is in common anode (cathode
follower) configuration.

All in all, might not be a bad distortion box, especially if you have a
preamplifier *before* it (such as a preamp built into your guitar). If
you're really curious, build it up and play around with it. Note however:

1) The polarities of D1 and C3 are backwards.
2) I'd experiment with the grid resistors R1 and R4 to the cathode
return (top end of C3) instead of the positive ground. It will probably
result in less distortion, but a different "quality" of distortion.

Another one that uses a single 12AX7 is my "Real McTube", which operates
at a considerably higher B+ (but still significantly lower than most
hi-fi preamps). http://www.dogstar.dantimax.dk/tubestuf/mctube.htm

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects, Vacuum Tubes & other stuff: |
| http://www.dogstar.dantimax.dk |
+--------------------------------------------+

In article , "michael bateman" wrote:

I'm looking to build a battery-powered tube preamp for guitar, and I came
across this schematic:

http://guitarrage.virtualave.net/eff.../eti83_tube_di
stortion.html

I'm no tube amp expert, but this seems weird to me. All of the other 12AX7
designs I'm familliar with have high voltage (150 - 450V) on pins 1 and 6
and grounded through 3 and 8.

The schematic I linked to connects pin 1/6 to ground and pin 3/8 to -15 V,
and has no high voltage indicated. I know enough to say that the electron
flow through the tube should be the same for this design as the other, since
pin 1 is still positive compared to pin 3, but I'm at a loss to figure out
how this circuit works without a high voltage source. I mean if 15 volts
will give a working (and decent sounding) circuit, why does every other
design I've come across use such high voltages?

Any feedback appreciated: Especially any links or info that might help in
building a battery-powered tube preamp.

The ETI 83 is not very good for guitar. I Think it was aimed more towards synths but you never
know with ETI. They were an odd company, but came out with many intresting things. Alot of people
Dislike the sound of starved tubes, i like them clean or with very mild distortion, but the more
distortion you add the worse they get. But if i am right and this was amde for synth use, it would
most likely be fallowed by other moduals, like Voltage Controled Filters and such wich would change
the sound alot. Check out paia for information of starved plate tubes, i think they have an article
on it with their TubeHead Preamp, but i might have read that in the manual, that could be there
also. www.paia.com

adam

On Mon, 11 Aug 2003 22:10:53 +0000, michael bateman wrote:
....
I'm no tube amp expert, but this seems weird to me. All of the other 12AX7
designs I'm familliar with have high voltage (150 - 450V) on pins 1 and 6
and grounded through 3 and 8.

The schematic I linked to connects pin 1/6 to ground and pin 3/8 to -15 V,
and has no high voltage indicated. I know enough to say that the electron
flow through the tube should be the same for this design as the other, since
pin 1 is still positive compared to pin 3, but I'm at a loss to figure out
how this circuit works without a high voltage source.

If you look at published tube curves, you'll
often find that both ends of a curve look
wonky - but they're still shown. Current flows
fairly easily in a vacuum, so you should get
*some* current at almost any voltage level.
The problems you run into are (a) the tube
is no longer operating in a linear region and
(b) it can be diffficult to tweak the bias.
At least with a low voltage, low current supply
you won't fry the tube. 8^)

This goes along with what Jim Anable said
about tube selection. The farter towards the
end of teh curve you get, the more a minor
tube difference becomes a major one.

I mean if 15 volts
will give a working (and decent sounding) circuit, why does every other
design I've come across use such high voltages?

Working (as it in passes and controls voltage
and current) does not equal decent sounding.
Most of the extremely low voltage designs I've
heard using tubes like the 12AX7 were not all
that great, in my opinion. Then there were
others that really sucked...

Are all Chandlers low voltage? If so, I have
heard one I really liked. Unsurprisingly, it
was in use by Eric Johnson on stage. 8^/

The voltage you need depends on a variety of
things. Old AM car and portable tube radios
ran off relatively low B+ (40-90V). But then
again, AM radio bandwidth is fairly limited,
it's prone to noise, and people just don't
expect that great sound from it. (They could
have run at 6V or 12V, but then you need a
lot more current for the output tube!)

Hi fi designs are probably the pickiest of
the audio applications (surprise!) for plate
voltage, but guitar amps are picky, too. I
personally prefer guitar amp 12AX7s run at
higher voltages (say, 150 and up). I also
generally prefer my 6BQ5s (EL84s) run as high
as possible. 250V is, to me, the 6BQ5 low
end, whereas some people never go above that.
I am usually unhappy with 12AX7 preamps run
below 100V; they start to come alive around
130V to 150V. 180V-220V is even better, IMO.

But... they'll function at 15V. Whether they
sound good is up to the individual listener.
It's probably worth checking out just to see
how *you* like it.

-Miles

On Wed, 13 Aug 2003 05:27:00 GMT, Miles O'Neal wrote:

Are all Chandlers low voltage? If so, I have
heard one I really liked. Unsurprisingly, it
was in use by Eric Johnson on stage. 8^/

Yes they are. David Gilmour has (had?) 2 in his rig, as well. I have a
floor model that sounds pretty decent. I sold the rack model I had for
$255 (???). eBay record, I think.

-Dave

I put a Telefunken ECC83 in mine (Chandler Tube Driver / orig. BK Butler,
no wall wart) years ago and have been consistently pleased w/ the
OD/distortion component of my patches. The closest hmmm- not bad I tried
was a box called a Voodoo.

The one which I think may finally have a chance at eclipsing the Tube
Driver's incredibly long reign is the ToneBone Classic. I've been
looking at them for a while now, yet haven't had the opportunity to trial
one. Interestingly, I noted that they got a rave endorsement from EJ.
Now I wouldn't be surprised to learn that Gilmour has one too.



Dave Curtis wrote:

On Wed, 13 Aug 2003 05:27:00 GMT, Miles O'Neal wrote:

Are all Chandlers low voltage? If so, I have
heard one I really liked. Unsurprisingly, it
was in use by Eric Johnson on stage. 8^/

Yes they are. David Gilmour has (had?) 2 in his rig, as well. I have a
floor model that sounds pretty decent. I sold the rack model I had for
$255 (???). eBay record, I think.

-Dave