Submini Tube Amp Project (Edited w/ more questions)

[Kevin Mitchell]

Okay...

On amazon of all places I found "OSD Audio SP70T 70-Volt Commercial Line-Matching Transformer" for $15USD!


Is this the American version of the Transformer you were talking about? Or will it work just as well?

Wouldn't it also work as a reverb transformer if I don't use the center tap?

Also... If I'll be giving it upwards to 200 volts from the SMPS wouldn't that be an issue? This is what I'm not understanding right now.

[Kevin Mitchell]

I apologize if my constant updating bothers anyone. I've been trying to wrap my head around tube amp topology and transformers all day.

Though those links have great information I don't understand how it all works even though I just read through everything! As I said I'm a noob 

I do however understand that people have claimed to have successfully applied these 70-100volt power transformers as output transformers. If I can get away with using a $5 transformer of course I'll try! I've found this as well;
"70V 15W Speaker Line Matching Transformer" under $5!
There's also a 10w one that also has a 5w lead - for even less $

My concerns are if I would have to modify the transformer or if it becomes more trouble than it's worth to an amateur stompbox guy like myself. And also nothing (especially audio quality) is being greatly compromised.

Is this something that you have tried yourself? Most output transformers are described as "tube output push pull". The links you have shared suggest there wouldn't be implications using one of these 70volt line matching transformers as a substitute for such a tube amp project if I understand correctly.

EDIT: I found this looking into using this as the reverb transformers and found great information. I say it's well worth a shot for the output and even the reverb transformer. People have reported have success in either possition! I can't see why not both. But of course there's likely many variables to consider.
Ehh I put up the wrong link. Will fix later.

There's allot of information about the workings of a transformer and it's roll in an amp as well as using these cheap transformers for a push-pull circuit. Seems promising and worth a shot - saving a large chunk of dough.

Ahhh now it's coming together.

[thomasha]

Nice that you found cheaper versions!

on the other side of the atlantic the hammonds are really expensive and this line transformers are a good option for push pull output stages.

As for the reverb, there is always the problem that the reverb requires a SE transformer, that needs an air gap to avoid saturation. I haven't used one of this line transformers, but I used a 220v to 6v transformer with good results, even in SE, but I haven't measured the frequency response of it. The thing is, some guys open the transformer and change the lamination arrangement. I tried amps with this rearrangement and without it and it's hard to identify some difference in tone, but when using a good SE transformer the difference is huge.

Just one thing, I like the 5w transformers because they're smaller (the 125a is still smaller but the price...) and all my builds are mostly in small pedal enclosures or mini combos.

I think the fender reverb from the link that I sent you is really small and  there are some equivalent versions that are cheaper, you just need to look at tubesandmore, mojotone, angela and the other amp stores and search for a 22.5K primary to 8 ohms or 11.5k to 4 ohms and it will work.

[duck_arse]

just in case you are passing a jaycar ....

http://www.jaycar.com.au/Power-Products-Electrical/Power-Conversion-%26-Transformation/AC-AC-Transformers/5W-Line-Speaker-Transformer/p/MM1900

[amptramp]

If you have a 70.7 volt transformer, the 1 watt setting gives you a 5 Kohm impedance, 2 watts gives you 2.5 Kohm etc.  The 5 watt tap gives you a 1 Kohm impedance and most tubes, even most triodes, require more than that.  Line transformers are cheap and plentiful, so I have used them in a number of projects of my own.

Make sure if you are using the transformer in a push-pull output that you have the necessary two windings with the correct voltage split.  I have a Burtek T7010C transformer with 0.625, 1.25 and 2.5 watt taps to the common ground.  The resistance from common to the 0.625 is 339 ohms, to the 1.25 is 211 ohms and to the 2.5 is 88 ohms.  The inner windings will of course have fewer ohms than outer windings, so you cannot get a guaranteed even resistance split and in a matching transformer, no one cares.

To run a balanced push-pull output, you need one tap with four times the power rating of another.  There is a common lead and tap leads.  The common lead is going to be one of the plate leads.  For the Burtek T7010C, one plate goes to the common, another goes to the 0.625 and the centre tap is the 2.5 (verified by voltage measurements using an oscillator).  This gives 2 K from plate to centre tap or 8K plate-to-plate, a very usable impedance, but not a very high wattage.  It is essential to have one tap at four times the wattage of another tap to get balanced push-pull operation.  You have that with the #300-039 transformer you have described but the 5 and 20 watt terminals give you 250 ohms on each side or 1 Kohms plate-to-plate.  This is very low for most tubes.  Even with the Burtek, you don't get the balanced resistances you would have with a transformer designed to be an output transformer.

I have used a number of these transformers with old (1920's) radios with a single-ended triode output and I even built a box with a transformer and a rotary selector switch to select impedances.  The DC current through battery tubes is too low to cause saturation, but for a power output, pay attention to the wattage ratings even when you are running push-pull.

[Kevin Mitchell]

Thank you so much for that information, amptramp.

I was just about to ask what wires I should use in respect to the superfly schematic. I was wondering what wire would be the choice for the primary's top lead and center tap.
This is a wire diagram of a 10watt 70volt transformer I will use for the push pull output.


Let's see if I got the wiring correct for the Superfly Special schematic with this transformer using the 5w lead...
Primary: 1.25w to the top tube's plate, .5w/5w is center tap and C to the bottom tube's plate.
Secondary: 8 ohms to speaker, C to ground
Everything not mentioned should be left unconnected.

I'm assuming here it wouldn't be a problem using a 10watt or 15watt transformer as long as the 5watt and 1.25watt wires are available (since I'll be using 5watts). Is this correct? I likely snag a smaller 5watt max one in the future - if I can ever find them.

[LightSoundGeometry]

im trying to work my way up to tube amps as well starting with sub-mini tubes ..I have the 5672 pretty well mastered but its only 5 nodes and too similar to a bjt so it was easy ..a triode is another beast it seems

I am following this thread with great interest ..and yes , we need a working layout, a place for us noobs to begin .

I have the fender 022921..which is slightly different than the 125A but exactly like the 1750a

and my speaker is reading closer to 12 ohms than 8 ohms ..and its a new 30 dollar 12" ..not sure how much the load affects the circuit between 2.4.8.16 ohms speakers

[Kevin Mitchell]

I just paid about $4 for the transformer I'll be experimenting with. A 125A is about $40 where I can find them so I'm very stoked to try this alternative.

I have also ordered a pair of 4 ohm 6.5inch Eminence speakers for ~$12 each! Submini twin reverb/tremolo blues amp... here I come 

I am following this thread with great interest ..and yes , we need a working layout, a place for us noobs to begin .

I've been putting great effort into translating these kind of projects to a language I can understand (or rather, learn a few foreign words). Break 'em down bit by bit till I can wrap my head around them. I do hope to have information to share with amateurs such as you and I so we can work on such projects comfortably. A hell of a transition from a stompbox though - I'm coming from no electrical background other than a couple years hanging around this forum and building and tweaking stompbox clones.

[LightSoundGeometry]

I just paid about $4 for the transformer I'll be experimenting with. A 125A is about $40 where I can find them so I'm very stoked to try this alternative.

I have also ordered a pair of 4 ohm 6.5inch Eminence speakers for ~$12 each! Submini twin reverb/tremolo blues amp... here I come 

I am following this thread with great interest ..and yes , we need a working layout, a place for us noobs to begin .

I've been putting great effort into translating these kind of projects to a language I can understand (or rather, learn a few foreign words). Break 'em down bit by bit till I can wrap my head around them. I do hope to have information to share with amateurs such as you and I so we can work on such projects comfortably. A hell of a transition from a stompbox though - I'm coming from no electrical background other than a couple years hanging around this forum and building and tweaking stompbox clones.

my goal was never pedals ..it was always tube amplifiers from day one. yes one hell of a transition ..the thing is there is no school that teaches this stuff .. you tube videos come the closest but they never get into any real detail on how to ..more of look at me and what I did ..Im not really book smart enough to follow along but am trying ..wish I had a real life mentor to pass along the skill to me..I need guidance and instruction , cant do this all on my own from some pdf files online ..

I am in school right now but I think school is now watered down and they dont really teach much anymore like they used to ..its a degree factory for funding ..its purely a business and the lower standards bring in larger numbers = more funding ....they could care less what you learn and what is taught ..all about keeping classes full for money.

my temper, I think I may need to let it go for a little bit and come back to it ...im scared of burning down my house..I had an awful smell the other day..scared something may turn into an uncontrollable fire

[Kevin Mitchell]

What I wanted in the beginning was to build a mini-moog clone. But I had nowhere to start. I'm a guitar player who absolutely loves to play with keys and synths. I get lost in playing with those much easier than with guitar.

I'm with you on the education stance. I want to go to a trade school to get certified and learn the basics but I will certainly not get all that I want out of it. But it would be nice to understand the language. I would absolute love to be an apprentice for an electical/audio engineer.  (pull my name Roger Mayer or Bob Moog!) lol  I often dream of being a tech roady.

You best keep an extinguisher at the ready. Only strange smell I've had was from what R.G. Keen calls an LEP I think "light emitting pot" Something on breadboard wasn't right and a pot as a voltage divider started to light up and smoke!

There's my rant lol. I need someone to prove my explanations on the 10watt transformer connections above.

[LightSoundGeometry]

What I wanted in the beginning was to build a mini-moog clone. But I had nowhere to start. I'm a guitar player who absolutely loves to play with keys and synths. I get lost in playing with those much easier than with guitar.

I'm with you on the education stance. I want to go to a trade school to get certified and learn the basics but I will certainly not get all that I want out of it. But it would be nice to understand the language. I would absolute love to be an apprentice for an electical/audio engineer.  (pull my name Roger Mayer or Bob Moog!) lol  I often dream of being a tech roady.

You best keep an extinguisher at the ready. Only strange smell I've had was from what R.G. Keen calls an LEP I think "light emitting pot" Something on breadboard wasn't right and a pot as a voltage divider started to light up and smoke!

There's my rant lol. I need someone to prove my explanations on the 10watt transformer connections above.

Paul in the Lab has a 5 watt amp using an opamp ..reviews says it pushes a 1x12pretty good ..cam across this searchign for something else. I think i might give it a go, he has a stripboard layout.

http://www.paulinthelab.com/2013/02/sparky-5-watt-amplifier-stripboard.html

[Kevin Mitchell]

Thought Paul was a colleague or something till I clicked on the link  . I've used simple 386 (LM, JRC) circuits to amplify synth stuff on breadboard and guitar on a few occasions. I might try Paul's circuit when I need it! Sounds super clean. Though it's not a tube amp. Gotta have that mojo. Well... I do 

[thomasha]

I need someone to prove my explanations on the 10watt transformer connections above.

I made some calculations for 70v and a 8 ohms speaker and ended up with this:

Zs         Tap
0        0 common
490       10
980       5
1960    2.5
3920   1.25
7903   0.62

One side must have 4 times the impedance, so i guess 2.5 would be the center tap, 0.62 and common for anodes;

the math can be found here>http://home.alphalink.com.au/~cambie/6AN8amp/M1115.htm

[thermionix]

im trying to work my way up to tube amps as well starting with sub-mini tubes ..I have the 5672 pretty well mastered but its only 5 nodes and too similar to a bjt so it was easy ..a triode is another beast it seems

I am following this thread with great interest ..and yes , we need a working layout, a place for us noobs to begin .

I have the fender 022921..which is slightly different than the 125A but exactly like the 1750a

and my speaker is reading closer to 12 ohms than 8 ohms ..and its a new 30 dollar 12" ..not sure how much the load affects the circuit between 2.4.8.16 ohms speakers

I'm not familiar with the 5672, but triodes are the simplest type of audio tubes.  Like a BJT with a heater, basically.  Plate (anode)=collector, cathode=emitter, control grid=base.  Anything less and you have a diode/rectifier.

If your speaker measures 12 ohms resistance, it is a 16 ohm (impedence) speaker.  You can use it in place of an 8 ohm, and nothing will be harmed.  You will lose a bit of volume from the impedence mismatch.  With a cheap speaker, you may lose much more volume due to low effeciency.

[LightSoundGeometry]

Thought Paul was a colleague or something till I clicked on the link  . I've used simple 386 (LM, JRC) circuits to amplify synth stuff on breadboard and guitar on a few occasions. I might try Paul's circuit when I need it! Sounds super clean. Though it's not a tube amp. Gotta have that mojo. Well... I do 

no, I feel you, MOJO WORKS ..I gotta have it myself ..even 600 volt orange dips and 10 dollar crystal diodes 

http://www.ebay.com/itm/1N39A-germanium-diodes-five-5-Vintage-Sylvania-very-rare-crystal-radio-/121940041538?

trust me , the pentode tube is the easiest ..almost too simple its not a good jumping board lol ..its helping though identify stuff etc.I guess it was okay, its teaching me two sources and have to watch I and E both ..learning the nomenclature etc 

https://frank.pocnet.net/sheets/138/5/5672.pdf


------------------------

what kind of synth is he using in Frankenstein ?  I always thought it ws some dude jamming out on a super moog

dude is rocken the synth lol

[thermionix]

(pull my name Roger Mayer or Bob Moog!)

Bob Moog is dead.  Just sayin'.

[LightSoundGeometry]

here we go ..will modify post as I go



b+ charge pump


about halfway through, decided to kick on power.. firey burn smell and tube lit up but I shut down quick ..does the tube itself maybe stink a little when it gets hot?



well it kicked on but wasnt real loud or sound particularly good ..its the 2 watt 18ohm resistor heating up and the tube smelling like fire/burning plastic



I dont even want to mess with this thing anymore ..that smell...I was hurt 16 years ago in a work accident so I get nervous really easy but it was stankin good and very, very, very hot

[thomasha]

the tubes get really hot, you could easily burn  your fingers.

My amp smells too, maybe it's the resistor, or maybe the tube, or both, if you think the resistor is too hot, you could use one with higher wattage or use two in parallel, same wattage, but double the resistance.

The 5672 has almost no glow, while the 6111 glows like hell, that's normal.

The sound is not very loud, and with a low efficiency speaker it will be even lower, so you can easily play after minight.

With a celestion 1x12 it's too loud for late night practice.

This amp should be very safe if you're using the right wattage resistor for the heaters. I burned like 3 of the IC's just by shorting the high voltage, so before you could start a fire it would burn the IC.

If you're afraid you should stop, or at least build the PCB version. With everything soldered it is much safer, and there are no crazy wires moving around.

[duck_arse]

if you get game enough to start it up again, measure the voltage across the 18R resistor, from end to end (it doesn't connect to ground, does it?)

then do ohm's law - P=V*V*R - and tell us what you get.

[Kevin Mitchell]

Are you guys playing around with the MAXX1044 charge pump? I'm planning to use the SMPS stetup with the 555. Perhaps I'll experience less fumes...
Oh I've noticed you're using a 5672. I'm sticking with 6n17B and for the power 6n16B or 6111WA.

I don't want to throw discussions off too much but I have a heap of LT1072 DATA SHEET "1.25A High Efficiency Switching Regulator". I'm curious to see if it would be of any use here. Bull I'll be sure to get the SMPS down first. I'll probably place a mouser order tonight. Then all I'm missing  is a reverb tank. Everything else should be on the way.

A couple of 6111WA tubes came in yesterday. They're very slim and as tall as my pinky-tip! 

Here's a concept of where I'll start off;

Ignore the second tubes connection  They're not wired right. I'm still working out the feedback (resonance) section also but that's for later down the road.

It has a simple fender tone stack and uncompleted for the sake of testing and adding a reverb circuit.