Transformer for Tube Pedals: Allied 6K1VF

[liquids]

Anyone ever use one of these?  I think I found out about it here.

I've been getting into amps recently, it all seems pretty doable.  This transformer would make it easy - for $16 (plus shipping etc).  And easier than the AC wall-wart + step-up transformer, Webers transformer (in a similar vein) correctly managing/tuning heater current and voltage, etc - at least to me.

With this, You could just get a power cord hard wired to one side of the transformer and mount it in/on a large-ish hammond type enclosure. put some 12ax7 tube sockets on top, wire up a simple  tube preamp via terminal strips and the tube sockets or otherwise, add a footswitch and tada.  MAybe not the smallest pedal, but for those who are sheepish, a good layout and you could fit it all/on in a 15950C, I'm sure.  

In my head I'd follow the gain stages  with an active op-amp based filtering via a separate DC jack power input.  Or at least use a passive tone control that doesn't have the typical mid scoop all the time (dumble or passive baxandall something).   Maybe make one of the stages parallel 12ax7s.  Yeehaw!

Seems doable.  One would need to know a fair amount about how to work with tubes to tweak it to get the frequency response/dynamics/gain you'd want, sure.  But it seems the sky is the limit and this transformer makes it DIY pedal-able, wheather you want vox, marshall, boogie, dumble, etc type dirt, if you know what you're doing.  

Worth it?  Not sure....hope to find out sometime!  Anyone game or do it already with this transformer in particular?

I'm itching to do it though I've got about a dozen projects in line already....    /    Maybe someday soon though...

[tubelectron]

Hi & Thanks,

This transformer is an interesting discovery to share - I record it +++.

1/ This would interest me more if these are available in 230VAC 50Hz : I will check it.

2/ You will have to shield it carefully, otherwise it will radiate the 60Hz hum in your stompbox and won't be able to get rid of it completely - trust me. So the sky is not the limit... But the shielding !

3/ let's hope it is correctly vacuum dipped, unless it will hum acoustically (laminations and coils vibration), which is sometimes unpleasant.

Nonetheless, good input !

A+!

[liquids]

Anyone know who makes these?  It's says allied but I doubt it.  Maybe Triad?  I'd like to get one sometime somehow, but not necessarily through Allied since it would be the sole thing I'm ordering. 

[Govmnt_Lacky]

Anyone know who makes these?  It's says allied but I doubt it.  Maybe Triad?  I'd like to get one sometime somehow, but not necessarily through Allied since it would be the sole thing I'm ordering. 

The datasheet says Hammond.

250VCT at 25mA.

Would that be enough for your circuit?

[liquids]

That should be plenty for the plates of 2 tubes / 4 tube stages.

[liquids]

The datasheet says Hammond.

I noticed that right after I posted this!    

However, I am yet to find something on their website that is the same - or at least, comparably cheap.   Maybe Allied will be the way to go.

[defaced]

25ma is more than enough for a 12AX& based circuit.  12AX7 triodes typically pull 1-2 ma  12AU7 is much higher at 10ma, but ultimately it's a design issue.  Get your load line out kids, lets play tube EE

[liquids]

Found another one http://www.allenamps.com/parts.php#transformers

"P2X - NEW! TP2X tube effects power transformer is rated 120V to 260V at 10mA (requires full-wave bridge rectifier) and 6.3V at 1A. Enough juice for (3) 12AX7 style preamp tubes for tube preamp and effects projects. 2-3/8" mounting centers. 1-21/32" tall by 2" deep by 2-1/16" wide across the end bells. 6" Unistrand pre-tinned leads. Made in USA. $25"

[liquids]

I'm ready to pull the trigger here, more or less...

I want to do active filtering on a tube pedal, though. 

The heater supplies for tubes are typically ~6.3volts AC, correct? 

So, if I Full Wave Rectify the AC heater supply (in addition to feeding it directly to the heaters), filter it significantly,  and likewise regulate the rectified signal with +/- 5v regulators, I'd have some decent power for op amps no?   

I'm assuming the average transformer with heater taps deliver more or less 6-6.3v RMS rather than peak, which  That should give +/- 8V DC when rectified and smoothed to feed the regulators, no?

A simple quad op amp should do...and save significant space and trouble over using more tubes as such.

Or would power mosfets be a better way to yield low-impedance signals / feedback for filtering?

[defaced]

At 6.3v, a 12A_7 tube required 300ma of current for the heaters.  Depending on your design, the heater winding may not be enough to power all of your low voltage stuff.  Grounding will be important if you use the heater for the low voltage DC stuff.  Bad juju happens if you ground the heater AC and the rectified DC, however the heaters may hum if they do not have a dedicated ground reference.  Heaters are sometimes used to run switching elements (LDRs, relays) because those DC supplies can float, but if you run signal through the low voltage stuff, they will need a ground too which can be problematic if the heaters hum if you remove their ground point.  You'll have to experiment to see what works. 

When you talk of active opamp filter, you're talking about an active (cut and boost) tone stack, correct?  Would high voltage MOSFETs work for this approach, IRF820, ZVN0545, etc?  I've used them for other things, but not for an active tone stack.  Watch the HV current load if you go this route.

I think Peavey has some amps (5150/JSX/XXX maybe?) that have active tone stacks.  Might be worth looking at how they did it.  Schematics are freely available. 

[head_spaz]

I agree. Using the heater voltage for active tone control could cause headaches, especially if you're planning to use opamps.
But this is a stompbox of sorts, no?
Last I heard, it's not illegal to use batteries or walwarts in stompboxes... not yet anyway. (as long as they're not made of Indian rosewood, Madagascar ebony, or trans-fats, you're good to go, for now. Heil the Great Seizer!)
But if it were my project, I'd add an AnTek 2 x 18V Torroid AN-0118 for the task. Anything worth doing, is worth over-doing. right? And for 10 bux it's a great deal. 2 x 18V windings, perfect for regulating to +/-15v rails. Or, you could go with their AN-0124, (same price) 2 x 24VAC and regulate it down to +/-22V -- then use NE5532's for even more headroom!
(They even have real tube type transformers starting around $25.00.)

Also, you might wanna checkout Carvin's Quad-X Amp, their old 4 channel guitar preamp has some pretty good 3-band active tone controls too. (just be sure to buffer the inverting input.) Schematic.pdf here

Good luck.

[MetalGuy]

1/ This would interest me more if these are available in 230VAC 50Hz : I will check it.

Similar transformers are available in Europe from Tube Town:

http://www.tube-town.net/ttstore/product_info.php/info/p2358_TT-Powertrafo-EI-230---200---6-3-7-VA.html

[liquids]

I agree. Using the heater voltage for active tone control could cause headaches, especially if you're planning to use opamps.
But this is a stompbox of sorts, no?

It started as a stombox.  Until I realized, why the aversion for a chassis-style preamp?  It eliminates the need for everything to be tight and conveniently pedalboard sized (which makes it prone to noise).  Adding a second transformer for op amp rails makes that all the harder.  Especially since I'm no pro.  I'd rather take up more space...to a certain limit.   So I am going to go with a straight up tube preamp chassis that sits on my amp or aside the pedalboard like an Echoplex!  Why not?!  And in that case, two transformers running off mains makes plenty of sense.

Last I heard, it's not illegal to use batteries or walwarts in stompboxes... not yet anyway. (as long as they're not made of Indian rosewood, Madagascar ebony, or trans-fats, you're good to go, for now. Heil the Great Seizer!)

I don't even use batteries in my stomp boxes.  I really dislike too many wall warts.  Heck, upgrading from a delay/reverb rack unit that used a wort to hard wired AC plug was a major selling point for me recently (and it sounds better but I bought it unheard!)  Running hard-wired AC wall power AND a wall-wort for said unit seems counter-intuitive at this point.

But if it were my project, I'd add an AnTek 2 x 18V Torroid AN-0118 for the task. Anything worth doing, is worth over-doing. right? And for 10 bux it's a great deal. 2 x 18V windings, perfect for regulating to +/-15v rails. Or, you could go with their AN-0124, (same price) 2 x 24VAC and regulate it down to +/-22V -- then use NE5532's for even more headroom!
(They even have real tube type transformers starting around $25.00.)

Thanks.  This got me thinking. I don't need such intensely high rails, though it's nice.  All I need is for the preamp's master volume control to run before the op amps so that it's back to matching 'bypassed' signal, and then I don't have to worry about too much voltage swing clipping the op amps.  But I do like bipolar power supplies for op amps.  And for active EQ, the extra headroom is a benefit.  +/- 9v may be sufficient, +/- 15v certainly is from what I've already done, and +/-12v should be enough.  I'll figure out the ripple/capacitance needed to smooth it out nicely (thanks to R.G. and his calculations) and pick.   Then it's a simple matter of the two approriate 2x 7?Lxx 100ma regulators - for a dual op amp or two for filtering and low output impedance at the end of the circuit, that will be more than sufficient.  

The antek seems sensible, but since the tube power transformers I'm choosing between are both 'allied' house brand products (cheaper than competitors and more than sufficient), I searched allied and found plenty of small equally cheap transformers that will yield dual rails, and center-tapped at that!  saves me shipping and that antek website is confusing at first.  The Allied 6K202HF is ~$10! 

Also, you might wanna checkout Carvin's Quad-X Amp, their old 4 channel guitar preamp has some pretty good 3-band active tone controls too. (just be sure to buffer the inverting input.) Schematic.pdf here

Good luck.

I know JUST how I want to active EQ - it's a favorite circuit realm of mine!  Cool link though.

So I'm very excited about this project.  But the shopping (on a recently tightened budget due to another purchase) has me running in circles, and I don't particularly understand power transformers.

Key Question I need answers to:

If I FWR (full wave rectify) the center taps of an AC transformer, how do I calculate the kind of voltage I'm going to see?  For the op amps, that one is 24V CT.  How many voltage DC is that going to yield?  Too high and it could blow certain regulators.

Likewise, when rectifying a separate CT AC transformer for the DC tube plate high voltage, I'm choosing between these two more or less-

A) http://www.alliedelec.com/Images/Products/Datasheets/BM/ALLIED_TRANSFORMERS/227-0001.PDF
B) http://www.alliedelec.com/Images/Products/Datasheets/BM/ALLIED_TRANSFORMERS/227-0113.PDF

What DC Voltage ranges am I going to get with these two options?  Likewise, for knowledge, a CT transformer that's listed like this:

https://taweber.powweb.com/store/022723sch.jpg

Is merely saying "640v" from one side to the other.  That means more or less 320vCT right?     There doesn't seem to be a standard way to list things.

[PRR]

WHY would you regulate for heater (just a dim lamp) or chip op-amps?

1,000uFd-220r-1,000uFd each side will clean-up rectified AC enough for several opamp chips.

That Weber "640V" is 640VCT, and they could perhaps say it that way. Other countries would notate that 320-0-320V. Used with two rectifiers and ample cap you get 450V DC. Used with a bridge you could get 900V DC with a 450V DC tap (except it may not be fully insulated for that connection). And that specific part is for a POWER!! amp, not a boxed preamp.

Allied 227-0001 250VCT is 125V each side. With 2-diode-and-cap plan you have about 160V DC. With FWB you could make 300V DC enough for a couple/three 12AX7. The 227-0113 is 500VCT and makes twice the voltage.

[markie83]

this may sound either really simple or really dumb..........BUT whatif since you have to have AC wired into this thing but dont want a wall wort you just put the wall wort inside the chassis and wire it to the AC your bringing in before the PT? 

[liquids]

WHY would you regulate for heater (just a dim lamp) or chip op-amps? 1,000uFd-220r-1,000uFd each side will clean-up rectified AC enough for several opamp chips.

Not planning to regulate for tube heaters....I was originally considering ALSO rectifying the 6.3vAC in part for chip-op amps because it's there, Sounds like that is a bad idea though.   Regulating rectified AC-->DC in addition to using filter capacitors is for things like improved noise, and potentially to get it the rectified DC down to a usable range that won't blow up op amps with certain transformers that might put out higher voltage than an op amp could take.  Regulation AND capacitive filtering yields even better results than just one or the other, from what I read.

That Weber "640V" is 640VCT, and they could perhaps say it that way. Other countries would notate that 320-0-320V. Used with two rectifiers and ample cap you get 450V DC. Used with a bridge you could get 900V DC with a 450V DC tap (except it may not be fully insulated for that connection). And that specific part is for a POWER!! amp, not a boxed preamp.

That transformer was just a handy comparative example, trying to understand the different ways transformers are listed; it was not on my list for use in this project.

Allied 227-0001 250VCT is 125V each side. With 2-diode-and-cap plan you have about 160V DC. With FWB you could make 300V DC enough for a couple/three 12AX7. The 227-0113 is 500VCT and makes twice the voltage.

Unfortunately you are confusing me more...2 doide and cap plan?  FWB?   But I'm going with the 227-0113/6K88 and bridge/full wave rectification in the end.

[Ronan]

>Key Question I need answers to:

>If I FWR (full wave rectify) the center taps of an AC transformer, how do I calculate the kind of voltage >I'm going to see?  For the op amps, that one is 24V CT.  How many voltage DC is that going to yield?

The centre tap goes to ground, and each outer winding feeds a forward biased diode, the cathodes of the diodes are connected together, this makes a full wave rectifier with only 2 diodes, the output DC voltage under load will be about 1.3 times 12V in this case (for a 24V CT tranny), so you will get about 15.6V DC. If you had a single 12V winding, and used a full wave bridge rectifier on it (4 diodes), you would get the same 15.6V DC.

>Is merely saying "640v" from one side to the other.  That means more or less 320vCT right?

Some transformers have a centre tap, some don't. A transformer with a 640V secondary will not have a centre tap unless it is stated, either 640V with CT, or 320-0-320. If the specs don't mention a CT or XX-0-XX then it probably doesn't have one. Some trannies are stated as having secondary voltages with two seperate windings, for example 2 x 120V. In this case, you can join the two windings to create a CT which would make it a 120-0-120. The output DC under load would be around 156V using the two diode rectification scheme with the CT grounded, or you could get twice that with a full wave bridge rectifier across the 240V (2 x 120V AC).

I made a tube pedal some years ago fed with a 10V AC wallwart, and inside the stompbox had a small tranny, to convert the 10V back up to high voltage, I had to shield it with thin aluminum plate to stop hum. I still have it and use it, 2 x 12AX7's. Around 300V +/- 50V is nice.

the box
pcb
top
under

[iccaros]

this one is rated 20ma per leg (so 40ma)
http://www.ebay.com/itm/250810379667?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649#ht_1323wt_1163

[PRR]

> you are confusing me more...

http://www.hammondmfg.com/pdf/5c007.pdf

[Ronan]

The output voltages on that Hammond chart look strange to me, I must be reading something wrong. Here's a good link:
http://www.freewebs.com/valvewizard/fullwave.html