2 X SE Output transformer in parallel ?

[Colas LeGrippa]

in order to use the transformers I have in stock, I was wondering if it was possible to use 2 SE output trannies in parallel, one for each power tube, with the secondaries joined together at the speaker out jack ??????????

[Colas LeGrippa]

..........without causing a planetary disaster ?

[stratele52]

Il y avait , la compagnie HARMONY  le modèle H440 , qui faisait cela pour le primaire seulement. Chaque lampe avait son transfo . Mais le secondaire alimentait chacun haut-parleur .
En fait c'était 2 lampes push pull sur chaque transfo , des 6L6 . Ça devait être assez puissant comme ampli et ils ne voulait peut-être pas investir dans un seul très gros transfo ?

Je crois que si tu mettait les secondaires en parallèle sur un seul haut-parleur ,on pourrais entendre un déphasage dans le son. Je crois que chaque transfo ne peut-être parfaitement identique dans leur bobinage et causer ce déphasage. Mais c'est une hypothèse. Et l'impédance ,  2 X 8 ohms en parallèle donnerais un 4 ohms ?  Oui en théorie.

Mais je ne pense pas qu'il y ait une catastrophe si tu l'essaie . Mais je ne veux pas être responsable  ; )

[Colas LeGrippa]

c'est ce que je pensais: un déphasage et des fréquences qui s'annulent. J'ai pensé aussi à utiliser sans problème apparent deux transfos pour alimenter 2 haut-parleur séparés mais là j'ai un problème d'espace: je joue souvent dans des espaces très restreints où j'ai presque une cymbale entre les dents tu vois le genre.............alors je dois utilier 1 seul haut parleur de 12 po. Je me commande donc illico un 125FSE de Hammond qui pourra alimenter sans prob mes 2 6L6. Merci de tes conseils.

Colas

[Willabe]

Why not just use 2 speakers, 1 for each power tube/OT and then add a 250K pot in place of the 220K grid return R for a master volume right before each power tube so you can blend the 2 as you like?

Could be very cool.


                    Brad      

[Dave]

I have run PP trannys in parallel with great success.

PP pair of 6L6 Output transformer (8 ohms)
+
PP Pair of 6L6 Output transformer (8 ohms)
=
4 X 6L6 into 4 ohms.

Dave

[Colas LeGrippa]

Hi Dave, do you mean that the secondaries of the two trannies are hooked up together ?

Colas

[kagliostro]

May be you are interested to read this old tread

http://www.el34world.com/Forum/index.php?topic=8471.0

K

[stratele52]

Hi Dave, do you mean that the secondaries of the two trannies are hooked up together ?

Colas

That's what I understand ColaLeGrippa

[stratele52]

Are you talking about SE transformers in a PP application? 
      

No,  ColasLegrippa want to use one single ended for each tube

[Colas LeGrippa]

t'as tout compris.....mais à la lueur de vos expériences et idées, ce n'est peut-être pas une bonne idée et comme j'ai besoin de cet ampli-là, je vais y aller sûrement avec un SE de 30 watts.
Salut.
Colas

[Colas LeGrippa]

J'ai quand même fait le test par curiosité avec 2 push-pull: annulation de fréquences, son très réduit et pauvre, 1 seul push pull : un peu plus de son mais nettement insuffisant pour la grosseur du transformateur

I am not gonna translate hey hey !

Merci

Colas

[stratele52]

Très intéressant  ton test Colas Legrippa.

[Colas LeGrippa]

Hi everybody, what a beautiful morning in Montréal !
Take a look at what ANGELA says on her site:

Hammond Universal Single Ended or Push-Pull Output Transformers Open style with minimum 5" long primary leads, secondary solder lugs for convenient secondary connections. Tables provided with each transformer listing 90 precalculated impedance ratios. Primary impedances from 1,200 to 25,000 ohms, so you can use virtually any output tube, single-ended or push-pull. The three primary wires obey the standard color code for push-pull output tranformers; the blue and brown wires are plate leads, the red wire is the center tap. For SINGLE-ENDED use of the output transformers in the 125 Series, simply use the two blue and brown plate lead wires; just tape off the red center tap wire. We have recently confirmed this hookup information with the technical staff at Hammond. Secondary impedances from 1.5 to 15 ohms. See this page for 125 Series Impedance Table. For more information on using this table check out the commentary on the Simple 6V6 Guitar Amp Project under the How To Section of this website.

If Hammond has confirmed the information after which we could use a push/opull output transformer as a single ended one , does it mean I can now use my car as a boat ?

[Colas LeGrippa]

The last sentence is mine, of course, hey hey !

[Willabe]

does it mean I can now use my car as a boat?

       

Not unless it's a duck.

[Colas LeGrippa]

oh I see, I can understand now why my amplifiers are motorboating.........

[Willabe]

oh I see, I can understand now why my amplifiers are motorboating.........

Oh, yes that's why.



                         Brad       

[Colas LeGrippa]

Hi again, hi hi hi hi .

SERIOUSLY NOW: I have performed  a second test with a GOOD PP output tranny. Red HV tap taped off, brown to both plates ( 2 X 6V6 '  paralleled  ) and blue to screen supply.
Plenty of power and tone. I tried with 2 X 6L6, but the PT is too weak ( PT from a Fender Champ hey hey don't wonder why ). When I got upstairs, a white smoke was everywhere in the house, while a cookimg pan was litterally dancing on the red stove, with my eggs that were gone in smoke. Too much excited and concentrated on tweaking that amp......
Gees' , one of these days...............My lady is nervous about me tweaking with 500V..........she oughta be nervous about me forgetting my meal on the stove,,,with no smoke detector.
( it wouldn't change nothing anyway, I am deaf...... )

Conclusion: If you have a PP somewhere and want to build a SE amp, you can use it with lots of tone. Next step for me now is to wait for my SE tranny and hook it in, to see the tonal difference.

[tubeswell]

I'd say its eminently feasible to put to SE OTs together to work as 2 halves of a PP OT. You hook up 1 output tube to each primary (as you would do with a SE OT) and connect the secondaries so that they were in-phase (which means that one of the secondaries would be 'backwards' - assuming the primaries were being 'fed' with opposing signals). BTW I've never tried this - I'm only supposing.

[jbefumo]

Stumbled on this thread searching on info regarding parallel output transformers.

Just finished my first single-ended amp design - 1 X 6L6 putting out just under 15 W into a Celestion 8" speaker - and am pretty happy with the result.

Was toying with the idea of an amp with both push-pull and single-ended power sections -- maybe a pair of 6V6s and a single KT88 for about 20-22 watts each. My initial thought was to use a 2X12 cabinet with one output section going to each speaker - maybe some combination of alnico and ceramic.  What I don't like about that approach is that it would not be compatible with any stock speaker cabinets, so am now pondering the possibility of running the outputs in parallel, 2 8-ohm transformers to a 4-0hm load (maybe 2 8-ohm 12s or 10s in parallel).  

The other reason I'd prefer this approach is so I can use an attenuator to facilitate pushing the output section to where you can actually hear any contribution to the tone.

Ultimately, I'm sure the only way to know for sure is to try it, so my main question is whether or not it's going to risk frying two costly transformers?

Thanks.

Joe.

[jojokeo]

I think I can hear PRR's thoughts while reading this thread? "Using all of this iron for it's unintended purposes seems like a waste of iron & money!? Unless it's out of necessity or "McGyver-ing" a situation." SE trannies have an air gap and are physically larger over PP types because of saturation issues. Be aware that tranny's have a phasing to them being the start & end of the windings like pickups do. Hammond's universal OTs are made specifically for multi-use puroses but single/specific use OTs were not designed for multi-use purposes.

[smackoj]

good pt. Jojo. i didn't know McGuyver built tube amps but if he does, i'm sure he is pleased with your 'hat tip' to him on the forum.   

[jbefumo]

I think I can hear PRR's thoughts while reading this thread? "Using all of this iron for it's unintended purposes seems like a waste of iron & money!? Unless it's out of necessity or "McGyver-ing" a situation." SE trannies have an air gap and are physically larger over PP types because of saturation issues. Be aware that tranny's have a phasing to them being the start & end of the windings like pickups do. Hammond's universal OTs are made specifically for multi-use puroses but single/specific use OTs were not designed for multi-use purposes.

Yup – aware of the  difference on OT types – happen to have a Hammond PP and a SE Excor on hand…

As to WHY . . .

Well, I look at tube amps as much akin to Harley Davidsons.  The basic technology has been unchanged for nearly a hundred years, but that doesn’t prevent people from doing some innovative stuff within the constraints of that technology. That means trying to apply the technology in idiosyncratic ways. Like the Harley, there are many newer, more advanced technologies, but within the sphere of what it was designed to do, they are still the best in many respects.

With tube amps, some of gone the way of hybridizing – introducing solid-state tone shaping components, computerized switching, and what have you.  There’s definitely some neat stuff out there, but for me, a key consideration is maintainability. I can look under the hood of my ’69 Chevelle, and there’s nothing I see that I can’t understand and, if necessary, repair or modify, but I digress . . . .

Sometimes one has a very specific goal in mind early in the creative process, other times, you just run on instinct and go fishing where the water looks interesting, ya know? There are aspects of PP amps I like – the punch, the immediacy; and aspects of SE, like a certain tactile feel, that is also alluring.

Not sure if combining them is going to be feasible, or worth the added expense and weight, but so long as it’s not destructive, I can always take it all apart and nothing is lost except a bit of time, and that’s offset by having learned that something DOESN’T work.

On the other hand, if the result adds a complexity of dimensionality to the sound, then I’ll experiment further.

Seems to me, if we weren’t into tinkering, we wouldn’t be HERE ;^)

[jojokeo]

Yep, not against exploring the great wide open. Wondering if anyone has ever tried running a PT in reverse for an OT??? Use the B+ w/ CT winding as the primary for a PP situation and the 117vac as the 8ohm speaker output. Any adventurer's out there willing to give her a try???

[jojokeo]

I would also re-think it using a CT filament tranny rather than the smaller wire on a B+/primary PT, better turns ratio likely too.

[HotBluePlates]

If Hammond has confirmed the information after which we could use a push/opull output transformer as a single ended one , does it mean I can now use my car as a boat ?

As long as Hammond built your car/boat. If not, you'd better continue to drive on the road, and buy a boat for venturing on the water.

The problem with using a push-pull OT in a single-ended circuit is the unbalanced d.c. Push-pull assumes zero unbalanced d.c. (or very little, like a couple-mA); having 10's of mA's of idle current eats up the cores ability to handle the magnetic flux, and results in core saturation and relatively little power transferred to the secondary.

So the exception would be a too-big (50-100w) push-pull OT being used for relatively little SE power (maybe 20w). It's also possible that with no air gap in the push-pull OT, even less power output could be handled (mainly because of the implied idle current).

I'd say its eminently feasible to put to SE OTs together to work as 2 halves of a PP OT.

Yes, but with the problems noted in RDH4, page 572 (available for download in the Library of Information):

"If the [push-pull] output transformer were replaced by two separate transformers, one from each plate to [B+], the even harmonics would not be cancelled and the other benefits of push-pull operation would be lost." (bracketed text added to clarify)

The "other benefits" mentioned are:
- Cancellation of unbalanced d.c. and a resulting reduction in size and weight of core needed in the transformer.
- Cancellation of hum at the plate of the output tubes.
- Cancellation of hum from bias supply present at output tube grids.
- Increased clean power output possible, because cancellation of even harmonics allows a lower load with the same (or less) distortion.

Since you may want more or different distortion, that may not be an issue to you. However, the weight, cost and hum penalties still apply.

[HotBluePlates]

Was toying with the idea of an amp with both push-pull and single-ended power sections -- maybe a pair of 6V6s and a single KT88 for about 20-22 watts each. My initial thought was to use a 2X12 cabinet with one output section going to each speaker - maybe some combination of alnico and ceramic.  What I don't like about that approach is that it would not be compatible with any stock speaker cabinets, so am now pondering the possibility of running the outputs in parallel, 2 8-ohm transformers to a 4-0hm load (maybe 2 8-ohm 12s or 10s in parallel).  

The other reason I'd prefer this approach is so I can use an attenuator to facilitate pushing the output section to where you can actually hear any contribution to the tone.

The intuitive approach is also the heaviest and most expensive. Do you really need 40w+ of power? Do you want to have to choke it down with an attenuator?

It occurs to me you might need separate power supplies for the KT88/6550 and 6V6's. That can be mitigated with careful design.

It seems easiest to have a push-pull OT for the 6V6's feeding their own speaker, and a single-ended OT for the KT88 feeding its own speaker. If you have OT's that allow easy switching of secondary taps, you should be able to use either or both output sections with any speaker cabinet. Using both in a single speaker cabinet (like a 2x12 or 4x12) implies at least "stereo" wiring of the input jacks of the speaker cabinet.

The only hard part is making sure you don't do something silly like leave one output section unconnected to a speaker when only listening to the other output section. 3 easy ways to fight that, but the best is to remove the output tube(s) of the section not being used from the socket.

You would presumably want a "master volume" control for each output section to adjust the volume contribution from each section, so another easy way is to turn down the volume of the section you're not using. But you might forget to turn that down, and leave drive to an unloaded output section, potentially causing voltage spikes in the OT.

You could add a largish resistor from hot to ground of each speaker jack, say 150-200Ω. That's too big to draw any real power when a speaker is plugged in. Downside is they'd have to be rated for double the section's likely output power, and playing hard with the section's volume turned up and no speaker load cause be hard on output tube screens (and maybe the OT). Still, it might be a handy backup to indivudal output section volumes in case you forget to properly set things.

Versions of this have already been done before. Mainly I'm thinking of how reverb send signal is sometimes tapped from the speaker output of an amp, which drives a reverb tank, and a follow-on boost and amplifier output section which ultimately drives its own speaker. This was done by some amp companies back in the 60's, and THD once produced a Bassman-type amp with reverb that fed one of the speakers in the combo cabinet.

[jbefumo]

Oh - wasn't thinking of using a PP transformer in a se circuit . . .

Talking about two separate  transformers, each for its appropriate  circuit.

As for power, I don't consider 40W excessive.  MOST of the time I'm looking for the best clean sound I can get, and for that, I found 40W about right for playing at drummer-levels.

I've used attenuators for years, though I never dime my amp or come anywhere close.  It just gives me one more option for dialing in the tone I want.

If Hammond has confirmed the information after which we could use a push/opull output transformer as a single ended one , does it mean I can now use my car as a boat ?

As long as Hammond built your car/boat. If not, you'd better continue to drive on the road, and buy a boat for venturing on the water.

The problem with using a push-pull OT in a single-ended circuit is the unbalanced d.c. Push-pull assumes zero unbalanced d.c. (or very little, like a couple-mA); having 10's of mA's of idle current eats up the cores ability to handle the magnetic flux, and results in core saturation and relatively little power transferred to the secondary.

So the exception would be a too-big (50-100w) push-pull OT being used for relatively little SE power (maybe 20w). It's also possible that with no air gap in the push-pull OT, even less power output could be handled (mainly because of the implied idle current).

I'd say its eminently feasible to put to SE OTs together to work as 2 halves of a PP OT.

Yes, but with the problems noted in RDH4, page 572 (available for download in the Library of Information):

"If the [push-pull] output transformer were replaced by two separate transformers, one from each plate to [B+], the even harmonics would not be cancelled and the other benefits of push-pull operation would be lost." (bracketed text added to clarify)

The "other benefits" mentioned are:
- Cancellation of unbalanced d.c. and a resulting reduction in size and weight of core needed in the transformer.
- Cancellation of hum at the plate of the output tubes.
- Cancellation of hum from bias supply present at output tube grids.
- Increased clean power output possible, because cancellation of even harmonics allows a lower load with the same (or less) distortion.

Since you may want more or different distortion, that may not be an issue to you. However, the weight, cost and hum penalties still apply.

[jbefumo]

Never thought about 40W as excessive, particularly if you need/want to play clean tones at even small-band volumes. 

I'm mainly a clean-tone freak, but that said, I've used an attenuator since my first Marshall PowerBrake. I generally don't like most master volumes.  With an attenuator, I'll typically crank it until it's just starting to develop some teeth - 60%-70% volume or maybe just a tad more, depending on the amp, then use the attenuator to throttle it back to the volume I need. 

I'm pretty sure with the right choice of transformer primary impediances, I could come up with a scheme to power both tube sets from a single power supply (though for experimental purposes, I'll just be using what's on hand.)

Actually, I just got this idea while playing through two small amps - the aforementioned 6L6 single-ended I just built, along with a Crate V18 (2 IL 84s) -- and found the combination quite pleasing. 

Joe

Was toying with the idea of an amp with both push-pull and single-ended power sections -- maybe a pair of 6V6s and a single KT88 for about 20-22 watts each. My initial thought was to use a 2X12 cabinet with one output section going to each speaker - maybe some combination of alnico and ceramic.  What I don't like about that approach is that it would not be compatible with any stock speaker cabinets, so am now pondering the possibility of running the outputs in parallel, 2 8-ohm transformers to a 4-0hm load (maybe 2 8-ohm 12s or 10s in parallel).  

The other reason I'd prefer this approach is so I can use an attenuator to facilitate pushing the output section to where you can actually hear any contribution to the tone.

The intuitive approach is also the heaviest and most expensive. Do you really need 40w+ of power? Do you want to have to choke it down with an attenuator?

It occurs to me you might need separate power supplies for the KT88/6550 and 6V6's. That can be mitigated with careful design.

It seems easiest to have a push-pull OT for the 6V6's feeding their own speaker, and a single-ended OT for the KT88 feeding its own speaker. If you have OT's that allow easy switching of secondary taps, you should be able to use either or both output sections with any speaker cabinet. Using both in a single speaker cabinet (like a 2x12 or 4x12) implies at least "stereo" wiring of the input jacks of the speaker cabinet.

The only hard part is making sure you don't do something silly like leave one output section unconnected to a speaker when only listening to the other output section. 3 easy ways to fight that, but the best is to remove the output tube(s) of the section not being used from the socket.

You would presumably want a "master volume" control for each output section to adjust the volume contribution from each section, so another easy way is to turn down the volume of the section you're not using. But you might forget to turn that down, and leave drive to an unloaded output section, potentially causing voltage spikes in the OT.

You could add a largish resistor from hot to ground of each speaker jack, say 150-200Ω. That's too big to draw any real power when a speaker is plugged in. Downside is they'd have to be rated for double the section's likely output power, and playing hard with the section's volume turned up and no speaker load cause be hard on output tube screens (and maybe the OT). Still, it might be a handy backup to indivudal output section volumes in case you forget to properly set things.

Versions of this have already been done before. Mainly I'm thinking of how reverb send signal is sometimes tapped from the speaker output of an amp, which drives a reverb tank, and a follow-on boost and amplifier output section which ultimately drives its own speaker. This was done by some amp companies back in the 60's, and THD once produced a Bassman-type amp with reverb that fed one of the speakers in the combo cabinet.

[DummyLoad]

Wondering if anyone has ever tried running a PT in reverse for an OT

yes. i do believe that one or two of our forum buds from down under have done so with low volt PTs.
IIRC one could use dual primary 120V to dual secondary 7.5V as as a P-P OT for a 8KΩ:8Ω - strap the primaries in series, (series connection becomes the CT) and the secondaries in parallel.

calculate the turns ratio based on voltage;
(240V/7.5)V = 32:1

convert to Z;
(240)^sq*(7.5)^sq = 1024*8Ω =~8.2KΩ:8Ω

calculate the turns ratio based on Z;
^sqrt(8000Ω/8Ω) = ^sqrt1000 = 31.622:1

the stuff they get down under is designed to run @ 50Hz so i don't think reproduction of the low octave of the guitar is going to be a problem, unless of course you're RicharD - he frequently tunes to a double A.

--DL

[jojokeo]

Wondering if anyone has ever tried running a PT in reverse for an OT

I was actually being sarcastic w/ that comment but it did seem possible even if it would be mismatched, and I thought someone would've tried it out there at one time or another.  I still go by my first comment w/ PRR's words of wisdom on things like this expressed as only he does. But with your calculations you confirmed my educated guess, thanks DL. I wonder what kind of performance & sound was to be had?

Messing around w/ various trannies in wierd unconventional ways just begs for trouble & needless expense. There's really not much to be gained even if lucky or carefully planned. With jbefumo's prior comment & happiness w/ his two amps dialed in the way he liked, why screw around? Just keep using the two amps that way. I think if you've been doing this long enough you realize there's only so much harmonic content to explore and when going beyond a certain limit it just begins to take on overdrive or distortion box properties. Things can become non-musical, unreliabile, fragile, tempermental, etc. Then you may end up with a one trick pony at best. JMHO

[DummyLoad]

I wonder what kind of performance & sound was to be had?

scroll down to bottom of page in link below - 3 sound clips.

http://jjs.at/electronic/class_ab_subminiature.html

--DL

[jojokeo]

  what a cute li'l toy

[kagliostro]

Hi Colas

is this your car ?

I really like the tone of red you have chosen

 

K