Tube boost + overdrive running off a 9 volt battery

[Yeahno]

- interstage gain pot - no more crackle - like a 'real' tube circuit.  Wink
- proper cathode biasing of both triodes - like a 'real' tube circuit

Adrian,

Can I presume that this is "better"? That is, does this explain why the tube runs hotter: because it is properly biased?  And by running closer to optimum due to biasing, does this explain why I prefer this circuit?

[Rick899]

Attached is a DIYLC  PNG  file pic of a layout of the DualCaster.  I know it is rather small but can anyone tell from it if  I got all the connections right. Or:   Will this work if I build it the way shown in the layout?  Thanks.

[Renegadrian]

- interstage gain pot - no more crackle - like a 'real' tube circuit.  Wink
- proper cathode biasing of both triodes - like a 'real' tube circuit

Adrian,

Can I presume that this is "better"? That is, does this explain why the tube runs hotter: because it is properly biased?  And by running closer to optimum due to biasing, does this explain why I prefer this circuit?

The above quote was written by Rick introducing his variation.
I don't know if cathode biasing can introduce the difference you say, maybe yes, but it's not only that I guess...
I'd say we should all go thru some already tested paths, as a lot has been done and can be used/copied successfully, just take (insert your favourite amp brand) preamp and play with its schem!

Now I don't want to talk tech more than I can do, but basicly you have hot tubes from the heathers (as their name implies I guess!!! XD), still I can see in Rick's variation an unusual 47k at the plates, while the common res. is a 100k. Can't tell you without experimenting what's the result in halving those plate resistors or if that gets you more heat.

just one of the tube preamps I've found - SCHEM

In those ckts as the Valvy itself, I'd get rid of the input cap, and have a 1M to ground at first and then a resistor to grid, usually you see a 68k, but I had some success going as low as 10k, a 22k or 33k is quite good!

I have been experimenting lately with Fenderish ckts at medium voltage, that makes me say a lot more can be done just starting from the basics!

[Rick899]

Renegadrian:

In regard to the freshly made vero layout of the Valvemster:  Are the green circles numbered "2", "5", and "6" mislabeled?

BTW:  Do they still have those Bibiti trucks all over Rome selling frozen bottles of water?   In Rome in July those frozen bottles of water really come in handy!

[iccaros]

- interstage gain pot - no more crackle - like a 'real' tube circuit.  Wink
- proper cathode biasing of both triodes - like a 'real' tube circuit

Adrian,

Can I presume that this is "better"? That is, does this explain why the tube runs hotter: because it is properly biased?  And by running closer to optimum due to biasing, does this explain why I prefer this circuit?

Just to help, I hope
as Renegadrian stated, you have heaters in the tube that do just that, they heat the cathode causing electrons (electron cloud) to boil off the metal, these electrons are then free floating in the vacuum until you have a positive charge that can attract them. The Plate is too far away for them to all go there so most fall back to the cathode. The screen or grid (pin 2 and pin 7) look like the screen on a window or door in concept. As you send signal to the screen, it is placed between the cathode and plate, and attracts electrons as it goes positive in comparison to the cathode. Since it has holes most of the electron cloud passes through and since its now accelerated it can reach the plate (anode).
as the tube conducts it draws current. this current draw over the plate resistor causes a swing in voltage which in proportion to the input signal based on how linear the the tube is operating.
Since the tube conducts based on how positive the grid is to the cathode, when we elevate the cathode with a resistor we make grid look more negative, so it takes a larger signal to cause it to conduct, and in our case a larger signal to make it overdrive.

All of that to say two things.. sorry
The heaters provide heat, the plate current can add heat, but at these low voltages they do not compared to the heater. The reason your tube may be hotter,  could be many, different tubes even in the same brand draw slightly more heater current making them run hotter . or two when you changed the design you moved a heater wire which gave it better connection and not its allowing more current to flow over the heater.

bias correctly was not the issue with the Valvecaster, and I think 1K is too much for this low voltage design, I am looking at ~500R. this is a better design because it removed the noise when changing gain, as no DC is on the pot.  There are many ways to change gain, in the valvemaster you change the limits in how much signal passes between stages, in the original you change when and how much signal the grid needs to conduct .

AS for 47K, this is a low voltage design, I like 68K for this, but I feel that 100K is too large, but its almost like a 220K on a normal design. As you lower resistance you lower gain, as you need the current passing through the resistor which causes the voltage swing, the more voltage the resistor drop the more the swing difference.. hope that makes sense.

[Yeahno]

Steve,

Just to help, I hope

Enormously.

All of that to say two things.. sorry

Not at all!

The heaters provide heat, the plate current can add heat, but at these low voltages they do not compared to the heater. The reason your tube may be hotter,  could be many, different tubes even in the same brand draw slightly more heater current making them run hotter . or two when you changed the design you moved a heater wire which gave it better connection and not its allowing more current to flow over the heater.

Got it.

bias correctly was not the issue with the Valvecaster, and I think 1K is too much for this low voltage design, I am looking at ~500R. this is a better design because it removed the noise when changing gain, as no DC is on the pot.  There are many ways to change gain, in the valvemaster you change the limits in how much signal passes between stages, in the original you change when and how much signal the grid needs to conduct .

Sorry, I'm not sure which you're referring to. You mean that you'd recommend exploring 500R instead of the 1K on the Valvemaster?  And do you mean that the Valvemaster is a better design?

AS for 47K, this is a low voltage design, I like 68K for this, but I feel that 100K is too large, but its almost like a 220K on a normal design. As you lower resistance you lower gain, as you need the current passing through the resistor which causes the voltage swing, the more voltage the resistor drop the more the swing difference.. hope that makes sense.

This sounds like mucking around with the 47K on the Valvemaster would be a good idea!

[iccaros]

Sorry, I'm not sure which you're referring to. You mean that you'd recommend exploring 500R instead of the 1K on the Valvemaster?  And do you mean that the Valvemaster is a better design?[\quote]
you asked if the valvemaster was a better design because its biased correctly before. I was saying that the bias adjustable is right to the valvecaster and its intended goal, so its not about right, just opinion, and I like a traditional cathode bias.

I am recommending between 400R and 500R for the first stage, I think the guitar signal is too low to get any overdrive @ 1K, I find that the first stage stays really clean, and I do not want that, I want a little overdrive (clipping) when I really hit the strings on the guitar, this makes it more "touch" sensitive in my opinion.

I like the Valvemaster design better, but  that is my opinion

This sounds like mucking around with the 47K on the Valvemaster would be a good idea![\quote]
I would try between 47K and 86K.. There are many ideals, and it changes based on the tube you use, a 12au7 responds differently than a 12ax7 or even than a 12at7, so you may want to try on a bread board first.

[Yeahno]

Sorry, I'm not sure which you're referring to. You mean that you'd recommend exploring 500R instead of the 1K on the Valvemaster?  And do you mean that the Valvemaster is a better design?[\quote]

you asked if the valvemaster was a better design because its biased correctly before. I was saying that the bias adjustable is right to the valvecaster and its intended goal, so its not about right, just opinion, and I like a traditional cathode bias.

Got it.

I am recommending between 400R and 500R for the first stage, I think the guitar signal is too low to get any overdrive @ 1K, I find that the first stage stays really clean, and I do not want that, I want a little overdrive (clipping) when I really hit the strings on the guitar, this makes it more "touch" sensitive in my opinion.

I just swapped in a pair of Vishay 499R (yes, 499...), left the 10uF caps in place and I'd say it sounds better.  More breakup, and as you said, more sensitivity to touch. With the volume knob on the Tele rolled back, it's clean.  Crank it and it starts to growl very nicely.

I can't tell you how much fun this is.

I like the Valvemaster design better, but  that is my opinion

As do I.

This sounds like mucking around with the 47K on the Valvemaster would be a good idea![\quote]

I would try between 47K and 86K.. There are many ideals, and it changes based on the tube you use, a 12au7 responds differently than a 12ax7 or even than a 12at7, so you may want to try on a bread board first.

It's all staying on breadboard until I've got something I like a lot.

Many thanks for the help and suggestions.

[Renegadrian]

Renegadrian:

In regard to the freshly made vero layout of the Valvemster:  Are the green circles numbered "2", "5", and "6" mislabeled?

BTW:  Do they still have those Bibiti trucks all over Rome selling frozen bottles of water?   In Rome in July those frozen bottles of water really come in handy!

layout corrected, thx for spotting!

yeah you can see those lil trucks all over the place! Damn!!! XD

[Renegadrian]

I can't tell you how much fun this is.

Now that's the best part of it!!! ;-)

[Yeahno]

Hmm.  Should I be able to swap in a 12AT7 tube for the 12AU7 tube in this Valvemaster circuit without making any changes?

[iccaros]

Hmm.  Should I be able to swap in a 12AT7 tube for the 12AU7 tube in this Valvemaster circuit without making any changes?

no harm will come if you do, and you may like it.. Tube rolling can be fun..

to answer more clearly, you can swap a 12au7, 12at7, 5751 and some 12ax7, with no changes.

[Yeahno]

So if I swap it into a working circuit and get no sound, suspect the tube?

[iccaros]

yes

[Yeahno]

Got a bad tube.  The dealer swapped it for a good one.

But now, whereas the 12au7 is nicely audible & crunchy, if I simply power off the circuit and roll the tubes, the 12at7's output is very low.  It's definitely working, but I have to turn the volume way up on the amp in order to hear it.  I'm thinking this has something to do with the performance characteristics of the tube and the impedance I'm presenting to it.

Must do some digging.

[iccaros]

These are low voltage design, or better termed as running the tube out of Specification.  I rolled through (4) 12au7 and (3) 12AT7 before I found the one that liked the low voltage. But I have other amps I can use these tubes in..
This is why professional designs either have  a voltage multiplier or a buffer before and after. So that no matter what tube is put in, it will perform.

[JRM]

Is this applicable with 12AX7?
thanks

In the article about driving triodes at low power that therminator posted, 12AU7 was considered to be the best one to play with because of it has a lower grid current and it's easier to bias (less sensitive).
An interesting statement on the article is the one on page 4 regarding Figure 7 and pull-up grid-leak biasing: it's the biasing method of Butler's Tube Driver.

[Teo87]

I'm gonna try changing some values to lower the mid/low ends!

[Yeahno]

In the article about driving triodes at low power that therminator posted

Link?

[iccaros]

its in my first post
http://www.diystompboxes.com/smfforum/index.php?topic=91745.0