Sub mini tubes question

[demym]

Hi to all,

after some month of exploring own stompbox building i am quite satisfied. I've done mainly JFET pedals: BSIAB2, a CarvinLegacy emulation, a Thor and a Tillman. I also bought Brian Wampler's book, and that explained me a lot of things i've read here before.

All my actual builds sound very good to my ears (i used to play, and still do, a rocktron voodu valve for live performance, a machine i love for tones flexibility and for midi foot management).

At this point i would like to experiment more: first, powering my JFET pedals at more that the usual 9V (i've read that the sound is much more amp-like).


Yesterday i came across discussions about sub mini tubes; as i'm really afraid to do high voltage projects (but i really would like to..), i have some questions about mini tubes:

1) could they be powered at low voltage ?
2) as i've seen that in some cases a MAX1044 is used to get more voltage from a 9V battery, does this require use of a transformer ?
3) are cascading stages rules valid also for minitubes ? (i mean, taking the ROG tube4fet and applying it to minitubes)
4) is the sound 'tubish' ?

These are simple beginner questions that i didn't see answered specifically in the threads i've read.
Hope that the answers could be simple.

Thanks very much in advance

Demy from Italy

[liquids]

I love Jfet stuff.  MY main pedals for about a year, since I started DIY have been 2 moded BSIABs.  I've gotten a fair number of tone compliments for the few times I played out, and regardless have been happier with my tone, feel, range of distortion, dynamics, etc, than ever before.

I've been modifying a EH English Muff'n pedal which is a basic 3-stage tube preamp, inside a pedal box.  It runs at high voltage (~240v) which is reasonable for most amp pre-amps. So it has the sound of tubes.

I've modded the EH pedal quite a bit.  I've gotten a good sound out of it, even.  And I will continue to do so.  However, in the end, I'm sticking with 'JFETs'!  SRPP stages in particular.  I think I actually prefer the sound and manner that they break up.  If not, they are so close, can sound so good, and are far far easier to work with that it's negligible so long as you know how to work with them.    The benefits of working with tubes, sub-mini or whatever simply for a 'good distortion sound' are negligible, if not non-existent, if you ask me.   I'm keeping my EH English Muff'n, but probably not going much further with tubes.  However, if you want a tube project, that's a pretty good starting point since the difficult stuff (HV transformer, layout, etc) is taken care of and it can be heavily modded.

Anyhow, back to jfets.  If you want higher voltages, Use a LT1054 - ignore the Max1044.  That seemed to be an early charge pump and there's lots of post on it from years prior.  I don't know your supplier, but the LT1054 is cheaper, available on both mouser and smallbear, and straight up superior.   Futurlec does not offer it, if I recall, but if you can at all get it for a fair price, choose it over the max1044, and google the datasheet, and you'll be golden.   No matter what, you'll need some 50v electrolytic caps and get a bunch of schottky diodes too.

I would encourage you to get to know how to work with jfets/mu-amps/SRPPs, etc, using charge pumps up to about ~24 volts.  It's actually fantastic to be able to have realtime control over the voltage of such stages, via a pot rather than just 18v, 9v, or even just one or the other, even if just to get a feel for what happens along the voltage range.   A lot happen between 5v and ~18v!  

I'll give you some generalizations I've gotten with JFETs and voltages.  Saying things get more 'amp like' at higher voltages is only true to a point.  Which amp?  I get certain amp sounds better at 6v than 18v.    

9v sounds good, and is probably what you are familiar with, so I'll use that as a reference.  As you go down from 9v, things get 'lo-fi.'  The bass becomes warmer and spongier, the highs get sweeter/duller.. The feel is a little more compressed, though the available 'gain' goes down.  It all happens at once.   As you get to 9v and up, the opposite.  The highs get clearer, and the bass gets 'tighter' but bigger.  You increase available gain, while simultaneously the dynamics increase - you can get more potential 'clean up' from your guitar's volume knob, for example, if you control the gain to similar levels along the voltage range.  

Also, note - tubes or jfets, etc, filtering of some kind is a must.  Running a tube preamp at high voltage into an amp is a pretty harsh sound, and makes you wonder how people think tubes are 'warm' sounding!   It begs for high end filtering.  Same with JFETs.  

[petemoore]

At this point i would like to experiment more: first, powering my JFET pedals at more that the usual 9V (i've read that the sound is much more amp-like).
 12vdc's cool on some effects, make sure your applied voltage is <the rated component value, less by about 10% margin.
  Yesterday i came across discussions about sub mini tubes; as i'm really afraid to do high voltage projects (but i really would like to..), i have some questions about mini tubes:
1) could they be powered at low voltage ?
 Some were designed to run in my Cadillac's AM/FM, 12v supply or some such, known as very super-radio-tone in that car, wish Idda kept her, loud, beat-down gas-hog she was, a car battery tube amp is cool.
2) as i've seen that in some cases a MAX1044 is used to get more voltage from a 9V battery, does this require use of a transformer ?
 schematic? the data sheet shows cool tricks the MAX can do like reverse polarity, voltage doubling, other applications. I think they're oft used instead of or to avoid use/need/cost/weight[?] of transformer[s.
3) are cascading stages rules valid also for minitubes ? (i mean, taking the ROG tube4fet and applying it to minitubes)
 Yes, you're talking seriesed gain or buffer stages, like as in preamp.
 Tubes and Jfets have a lot in common, the Jfets, 12ax7's and other various tubes can be used for gain and buffer stages in preamps. I think a well worked out mini or submini tube preamp or Jfet>Tube type preamp is a great idea. Small signals, low-ish voltage, tubes, whatever else thrown in for extra dirt-like features.
4) is the sound 'tubish' ?
 Tubes can be made to alter waveforms, guitarists report having found fond tones with them.
 Tubes will be tubes, these are tubes, after trying ___ is almost always when we know more, the data sheets tell stories about tubes too, secondary reference to understand them is recommended, study the words like plate capacitence, max plate voltage, db gain, access to reference reads while data sheets and schematics are studied is recommended.
These are simple beginner questions that i didn't see answered specifically in the threads i've read.
Hope that the answers could be simple.
 A printer's wallwart might be 30vdc, which is 'safe' to work with.
If the WW power supply DC is too ''raw'', noisy, regulate and filter for ''pure-er'' ripple free DC.
 Another WW power supply for the tube heater filament can work, or add regulator here too, stay within +/- 10% of the heater voltage requirement, measure the voltage loaded down with the filaments connected, drawing current.
  Jfet or tube or bipolar or opamp, the first active stages after the pickup are sure worth fiddling with, swapping for to find the 'right' ones. I'm fond of guitar pickup sees Jfet gate, a ~Strato-blaster indicator LED has been on a lot since last month, bigger gate resistor.

[frequencycentral]

1) could they be powered at low voltage ?

Generally yes. However, I've found that high mu triodes (6112) don't work well at low voltage.

2) as i've seen that in some cases a MAX1044 is used to get more voltage from a 9V battery, does this require use of a transformer ?

No. But make sure your total plate current doesn't exceed the current output of the charge pump

3) are cascading stages rules valid also for minitubes ? (i mean, taking the ROG tube4fet and applying it to minitubes)

Yes.

4) is the sound 'tubish' ?

This is subjective. Tubes at low voltage sound pretty good to me.

[demym]

Great, guys !

Just another one: can you point me to a simple at least two stages schematic at low voltage with sub mini tubes ?

Is it simple to take, say, a minibooster schematic (or other SRPP or Fet4Tube)  and transform it for use with sub mini tubes ?

I imagine that one could also take a one sub mini stage and combine it with fet stages, right ?

Thanks, anyway for your many answers

Ciao

[frequencycentral]

Subcaster is a good place to start: http://www.diystompboxes.com/smfforum/index.php?topic=63479.msg506137#msg506137

[petemoore]

 Jfet Stratoblaster [2n5457] or other can make a preferred 1rst stage. The pickup source is rather weak, it's convenient, Jfet's do super job here IME, tube is fine too.
  The second, and successive stages which see a boosted signal, begin to reveal their ''characteristics'' more noticably, component choice determining to some degree what parameters produce what results [compression, harmonics, distortion, artifacts, etc.].
 

[PRR]

All tubes "work" at low voltage.

But all tubes are high-resistance devices. Low voltage and high resistance means very low current. Low voltage and very low current means very-very small power output. We don't talk about the "power" of a pedal/effect, but you have to deliver a strong enough signal for the main amplifier to work with.

> I've found that high mu triodes (6112) don't work well at low voltage.

That follows. Mu is ratio of plate impedance to cathode impedance. For a given cathode size/heat, all tubes have similar cathode impedance. A high-Mu tube has a higher plate impedance, and thus even lower output power. As you found, perhaps so poor that it can't do the job.

There's also a question of why you would want hi-Mu at low voltage. Say your signal is 0.2V and your hi-Mu tube could give a gain of 50. The output would be 10V.... which can't happen with a 9V supply, and is unlikely even at 18V. Since your input is a "given" and your output must be "small", hi-Mu tubes are usually not a good fit.

Why sub-miniature? There are two general kinds:

Bomb-tubes: these are ordinary 12AU7-like guts in small baseless bottles. They are compact, but power-hungry, and hard to find.

Hearing-aid tubes: these are extra-teeny guts for long battery life. The available power even at 22V is quite small. And these are hard to find.

Build with plain old 12AU7. There are "better" tubes for low voltage, but the AU7 is easy to get, and fairly tolerant of low voltages.

[Renegadrian]

I quote Rick and Pete (precious info on their posts as always) and say CIAO to a fellow italian...

[demym]

Many many thanks to all ! Now i have at least some basic (and maybe more) informations. Just looked for some 12AU7 on ebay :-)

Ciao to my 'compatriot' Renegadrian (I've read about your projects, not bad as a learning progress from the beginning !)

Cheers, Demy

[frequencycentral]

Bomb-tubes: these are ordinary 12AU7-like guts in small baseless bottles. They are compact, but power-hungry, and hard to find.

Just looked for some 12AU7 on ebay :-)

Don't be put off submini tubes. 6111 and 6021 are not that hard to find on ebay. There's also no reason for them to be more power hungry than standard tubes. Two 6111 with the heaters in series powered from 12 volts draws the same current as two 12AU7. And you can do this with submini tubes ( it's a vibrato ):