Subminiatures

[tablebeast]

[quote author="analag"]

[/quote] So, what is this thing and what SubMinis does it have in it? Is there a schematic available?

Jesse

 

[Gus]

Looks like a headphone amp. Two 12V batterys, 24V? and a 1.5V for fil?

 

[analag]

http://www.dogstar.dantimax.dk/tubestuf/gallery4.htm#bear

It's a guitar amp?

analag

 

[tablebeast]

Wow, Zvex eat your heart out! I just got my 6418's in the mail today. I think I will build this circuit and see what it can do.

 

[Minion]

It is actually more like a Tube Guitar pre amp as it doesn"t have enough output to drive a speaker.....

Also those Tubes are 534AX which are a bit different than the 6418 tubes and even look bigger than the 6418 that I have....It seems that since these tubes aren"t made any more that some places are Chargeing Huge prices for them....I found one place that was selling these 6418 tubes for $15 each so If you can get them cheaper then I would get them.....


Cheers

 

[analag]

http://www.harmonicappliances.com/powerman/powerman.html
More stuff with the subminnies.

 

[tablebeast]

Where would I get a miniature transformer proportional to these subminis? Any suggestions? Also, I got a few of these 5784WB Subminis when I ordered the 6418's. What can I do with these? I can't find much on the net about them.

Jesse

 

[Minion]

Well I have seen Mini Audio transformers that were very small, probably simular to what is used in some microphones.... In the Design I am working on I use a Fet Buffer to lower the impedance from the Tubes and an opamp for createing a ballanced output as opposed to useing a transformer.....

Maybe something like this would be small enough:

http://cgi.ebay.ca/Triad-S-70Z-Audio-Output-Transformer-NOS-NIB_W0QQitemZ250028656897QQihZ015QQcategoryZ3284QQrdZ1QQcmdZViewItem

Or maybe something like this:

http://cgi.ebay.ca/Triad-S-18Z-Audio-Output-Transformer-Tube-Amplifier_W0QQitemZ220028040103QQihZ012QQcategoryZ67815QQrdZ1QQcmdZViewItem

These of cource are on the cheap end of the scale....

Or you can probably use a Microphone transformer from a cheap mic ...

You would probably have so talk to someone who knows for sure.....


Cheers

 

[rafafredd]

First find out impedance and power your design needs, than look for a suitable transformer. There are very small ones that sounds great. Do you want line output or speaker outputs?

 

[analag]

I'm trying to convince myself to build a sub-miniature tube mic pre with the ones I have. Pentode into pentode into triode buffer.

analag

 

[tablebeast]

First find out impedance and power your design needs, than look for a suitable transformer. There are very small ones that sounds great. Do you want line output or speaker outputs?

What I'd really like to do is build a belt pack based device that runs on cells so I won't need a power transformer. I have a lot of options for powering the 6418 which I plan to base this project on. A AA and a pair of 9 volts, a 22.5 volt, or a pair of 23A's. I'd like to get it as small as possible. The device would have a very short cable from the guitar to it. It would be a pre amp and a buffer so that I could then run a cable out of it to a guitar amp. That way I can run a hotter signal down the long run of cable: much like an active pickup setup already does inside a lot of guitars and basses. Would I even need a transformer for this? I am trying to score a few tube hearing aids and I think I will base a lot of my design on whats already going on inside those things, then adapt for guitar use. Wouldn't something like this allow the guitar to run at a very high impedance over the short cable run to the device and then send out a lower impedance signal over the cable to the amp, thereby picking up less noise and cable capacitance along the way?

 

[Minion]

You could possibly useing a Fet Impedance Buffer to lower the output impedance from the Tubes as opposed to useing a Transformer which is what I am trying to do with my Transformerless Tube preamp design.....

You could even probably use a fet input Opamp to lower the impedance and ballance the output.....

Just a thought since you are going for a small portable design.....


Cheers

 

[CJ]

I have a couple of UTC 10K:10K that some cool guy sent over.
Going to check response, small xfmr's are supposed to have the highest bandwidth.

 

[tablebeast]

[quote author="Minion"]You could possibly useing a Fet Impedance Buffer to lower the output impedance from the Tubes as opposed to useing a Transformer which is what I am trying to do with my Transformerless Tube preamp design.....[/quote]

Tell me more about this design. Is it an op-amp FET? What IC number? Do you have a schematic for your design to give me an idea of how to implement it?

You could even probably use a fet input Opamp to lower the impedance and ballance the output.....

Do you mean balanced output as in true low impedance? I was really looking to keep it unbalanced and not really have a true low impedance output from the device, just a LOWER impedance, that way the guitar and amp will have optimum connections. You'll have to forgive me if I seem ignorant about specifics, but I'm still a newbie to designing gear from scratch, I work better modifying existing designs.

I've always wanted a way to overcome the signal loss from the guitar to the amp because of cable capacitance. I figure this may actually be cheaper and better sounding than getting a couple of theose pricey Alessandro or Klotz cables. I would prefer an all tube design, two or maybe even three 6418's. Couldn't I use one of the 6418's as a cathode follower and that would buffer the output the way I want? Since I have no need to balance the signal I shouldn't need any transformers should I? Or is there something I'm missing? I noticed some of the hearing aid designs had output transformers on them and most of them use three tubes. Does anyone know where to get some schematics for battery powered tube hearing aid designs?

 

[Minion]

Hi, The Fet impedance Buffer will take a High impedance source Like that comeing from a Tube and covert the Impedance down to something in the Neighbourhood of between 50ohms to several hundred Ohms and can also be configured to boost the Gain comeing from the Tubes....

The thing about Fets is when the Clip they do so in a simular way as Tubes do which is why Fets and other transistors are now used in the Place of tubes (From what I have read).....

A Circuit like this should work ....

Which also has Provisions for Gain Boost but you might have trouble finding the 2N5571 like I did so maybe something simpler like this would be easier...

But this would probably have better Performance:

After the Fet buffer you can just use this simple circuit to create a Inverted (Ballanced) output...

But in a Battery powered situation you might want to replace the Opamp with a Lower power one like maybe the TL072 in which case you would replace the 10k input resistors to 22k (I"m sure there are better low power opamps than the TL072).....

I"m sure with the Schematics I posted in this thread you should have a Fairly good idea how to implement the Tubes and the Fet Buffer and the Ballanceing useing Mostly discrete components accept for the opamp as I had little more that this info to go on when I started with my tube pre design....

Here is a pic on my mostly stuffed prototype PCB..(Just have to wait for some High Value Resistors to show up in the Mail)

You can hardly see them as Tubes they are so small (and it is a ****** Pic)so you have to look closely but they are in the Top center and Right of the PCB close to the Yellow and white Polly Caps....

I think most of the designs that use these tubes use 2 or 3 tubes because these tubes do not put out very much signal so you might have to use a few to get the signal strong enough for output...

I use a Transistor based Front end to feed the Tubes a Strong signal and also built a Post Gain stage to boost the Gain from the Tubes even more....I have it set up so the First tube runs at Unity gain and the next one has adjustable gain , then I added the Fet impedance Buffer to lower the output impedance which then goes into a Clipping Indicator (Led) and then a 20db Pad and then it goes to a Dual Opamp for Ballanceing and then to output and useing ferrites on both the input and output for Interferance suppresion.....

I am feeding the Plate Voltage from a +48v Phantom feed regulated with a 10K resistor and a 20v Zenner (the plate runs from 15v to up to 30v with 22v being the recomended Voltage) and I run the 1.25v Fillament off of the +15v Rail useing a 1k resistor and a 1.5v Led as a Regulator......

I have no idea if the Circuit will even work but that I guess is part of the Fun of DIY.....

I"ve only been doing electronics for a few months so I don"t know too much so I get most of my Ideas from useing Parts of different designs and Throwing them together and I also just get Ideas that I have no idea how to implement so I just do what I think should work and Hope for the Best and sometimes it works great and sometimes I have to make a few changes to get it to work but more often than not the whole Thing goes up in smoke and Sparks but I don"t get discouraged for very long and I am usually blowing something up soon afterwords.....


But if there is something I can help you with just let me Know and I"ll try to do my best with the Limited knowlege I have.....


Cheers


PS: I also have quite a Huge Schematics collection so if there is something you need I might have it ...OOhhh I don"t have any Tube Hearing aid schematics...Sorry But I do have several Battery powered preamp schematics....

 

[Gus]

right out of the NS book.

 

[tablebeast]

I just scored a magazine article off of ebay that has a DIY pocket sized hearing aid project using all tubes. I imagine this will send me off in the right direction. I'd still like any other battery powered pocket size tube preamp circuit schematics if anyone has any. I will scan this article when I get it for all to see.

Jesse

 

[CJ]

A few items from the shrunken inventory dept.

Tele DF 703
Ray 2E31, 5678
Tung 5907
RCA 9004 thrown in for posterity

and a couple of UTC 80-223 M27/172 10K:10K xfmr's.

balanced in-balalanced out miny preamp, possibly...

are any of those tubes worth a darn?

cj