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A really simple starved plate tube booster?

Started by JimRayden, January 31, 2005, 01:07:42 PM

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JimRayden

January 31, 2005, 01:07:42 PM
Can anyone tell me, would the 12AX7 buffer or whatever it is sound good alone? Or is it ment only as a building block?

Here: http://xoomer.virgilio.it/luixssj3/index/elettronica/effetti/Distorsione/12AX7.htm

Can it be used as a simple clean booster or just use it to add a tube "magic" to my tone? Will it be clean or would it boost at all?

I don't know much about starved plate stuff, so can anyone explain?

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Jimbo

JimRayden

#1
January 31, 2005, 05:05:20 PM
Ok, I'm upping it.

The reason I'm asking the question is that I don't like the amount of solid-stateness in the Tube Driver. I wondered if I can use one half of an 12AX7 to make the guitar signal warmer and more tube-like. And then use the other half of the 12AX7 to build a bypassable identical circuit in front of it to overdrive it.

Does starved plate design boost the signal?

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Jimbo

Paul Perry (Frostwave)

#2
January 31, 2005, 06:07:22 PM
I'm not a tube guy, but that starved 12AX7 will definitely give a 'tube distortion' effect.
And I guess you can amplify somwhat with a starved tube too. The output impedance will probably be high, though.

JimRayden

#3
February 01, 2005, 11:53:29 AM
anyone know where the "fender-type preamp with horizontal tube mounting" project has gone? I can't find it anywhere on the net anymore.

And, if I use high voltages for the 12AX7, do I also have to use an output trannie? I think not though...

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Jimbo

puretube

#4
February 01, 2005, 12:06:55 PM
no OT for 12AX7  :D

JimRayden

#5
February 01, 2005, 02:20:52 PM
But still... can starved plate serve as a clean tube preamp kind of thing?

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Jimbo

casey

#6
February 01, 2005, 02:34:29 PM
check the "rubey tubey" or something like that...you should be able to find the schem. around here....

never heard it actually in action, but looks interesting...
Casey Campbell

JimRayden

#7
February 01, 2005, 04:47:04 PM
Can't find any. Though I found an 12v tube amp project. Was really cool thing. But still :P... is it possible to get good clean loud tube sound out of it?

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Jimbo

puretube

#8
February 01, 2005, 05:06:32 PM
search: ruby tuby

JimRayden

#9
February 02, 2005, 12:06:24 AM
Ok, now, i have been convinced that starved plate sucks :P. What rating of PT I need to make the 12,6V to large volts for the plates? Like 100-200 maybe?


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Jimbo

JimRayden

#11
February 02, 2005, 02:14:11 PM
...and some Q's still up...

I have bought a 220V to 12,6V with a 300mA secondary. Will this pass as a low to high voltage trafo for the tubes? Can the ampere tolerance of the 220V winding be calculated? I tried the most basic Ohm's law and a multimeter but it wasn't correct for the smaller winding...

Also, what the hell does the tube do in the Tube Driver? Some say starved plate tube circuits suck, but are they still better than a JFET simulation of a tube circuit?

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Jimbo

JimRayden

#12
February 02, 2005, 06:01:34 PM
up   8)

Sorry, it's a bad habit. I'm trying to quit...  :P


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Jimbo

javacody

#13
February 02, 2005, 07:56:08 PM
I wanna know too.  :)

Mike Burgundy

#14
February 03, 2005, 02:38:59 AM
The TD as published by Jack Orman produces a lot of distortion in the opamp. The tube then smooths things out.
I quite like it with a 12AU7 in there, everything running on 12V.
The problem with starved tubes is dynamics - which they don't have like a full voltage circuit does. They also have excaggerated non-linear behaviour - arguably distortion more like a tube.
They have a sound all of their own, if you expect high-voltage tube performance you will be disappointed, but they do have a certain sound, which is very useable and can be very right. There is no wrong here, just taste, and the way you apply it.

Transformers always lose a bit of power so you should use some percentage as a margin. I have no idea what is a *slim* but *safe* margin. Depends on the transformer itself, too.
If you use liberal helpings of available current, you should be fine. Also: that spec is rated at 12V and a certain amperage AT THE SECONDARY. The primary is built so it can support that, drawing whatever current needed to supply that secondary current. Sooo....if you get the secondary-turned-primary below dangerous levels, the 220V end will also be ok.

Lessee...datasheets are our friends
12AX7
12.6V @ 0.15A heater
250V @ 1.2mA anode

anode needs: 250V*1.2mA=300mW
take a margin: 500mW.
at 12V this would be:
500mW/12V=42mA
You might want to make some more allowances for peaks, rush-in currents (which aren't really there on the anode - the transformer itseld might introduce something though, and the filtercaps surely will) and stuff, but this suggests you could run two anodes - ONE TUBE - off of one 100mA12V to 220V transformer. Feels tight, but you could try it. Two tubes off a 300mA one should be ok.

so in 12V-land, we have:
100mA*12V=1.2W anode power
and
12V*0.15A=1.8W heater power. The heater does suffer (a LOT) from rush-in. Ever notice how lightbulbs always fail just when you swith them on? When the filament is cold, resistance is low and there is a huge current surge. A transformer can stand short surges to a certain point as long as voltage and current aren't too high, but still...
I'd say 5W total (1.2+1.8=4) per tube is *tight*, Id prefer 8 to 10W.
So, PER TUBE:
220-12V, 800mA
To heater, and to:
12V-220V, 150mA(@12V)

Should be safe and working, according to my not-so-scientific-but-educated guess ;)

JimRayden

#15
February 03, 2005, 07:46:29 AM
Thanks alot. Your post is going to be saved as a text file on my desktop. You've been really helpful.


Aaaaand another question.

http://www7.taosnet.com/f10/fender_pre.htm

Can a tube preamp also work as a stompbox? I mean, what are the preamps' output levels? And is the Fender Pre meant to overdrive the tube power amp that should be following it? I wouldn't like to spend all my allowance on an all-tube circuit just to find out that the output of a Fender pre will blow my little Roland out of the window...


Oh, and is there a mod kind of thing I could do to the Tube Driver to make the tubes overdrive, not the IC? Would it sound worse?

Can it be done by just removing one channel of the IC so I could have the IC boosting the signal and crushing it into the tubes?

Would it sound too bad?

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Jimbo

JimRayden

#17
February 03, 2005, 11:27:35 AM
Thanks alot. I'm going to study all the links plus some more and see if I can educate myself enough to actually do an attempt on designing my own tube circuit...

Any links where I could study the design of usual transistor circuits? Something a level above the ohms law and battery-resistor-bulb-designing tutorials... :P


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Jimbo

Ben N

#18
February 03, 2005, 02:08:46 PM
Take a look at this:
http://www.dogstar.dantimax.dk/tubestuf/mctube.htm
As built it is more like an overdrive than a clean boost, but so would a standard Fender preamp be without the tone stack attenuating the signal between stages.  Adjust the values and put in a tone stack (or just a voltage divider) and you should be there.

Come to think of it, that would get you pretty much here:
http://www.geofex.com/FX_images/alembpre.gif

Whether you want to be stomping on a high voltage preamp is up to you.

HTH
Ben
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JimRayden

#19
February 03, 2005, 03:04:33 PM
Thanks alot.

Ithink I'm going to build Tube Driver stompbox for now and afterwards build a Fender pre into a larger "amptop" case.

Thanks to all,

PS: whenever I have some other questions, I'll just use this thread again.

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Jimbo
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