Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Dave on January 06, 2010, 04:42:13 pm
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Hi all,
I have seen this question here before, but have never seen it answered.
I have a stereo power amp, I have run the output transformer secondaries in parallel to use the amp as a mono power amp.
Should I half the speaker load?
Dave
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Hi all,
I have seen this question here before, but have never seen it answered.
I have a stereo power amp, I have run the output transformer secondaries in parallel to use the amp as a mono power amp.
Should I half the speaker load?
Dave
Yes.
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Here's some info: http://www.tubecad.com/2005/March/blog0041.htm
If anyone understands it, please explain it to me! :book1:
EDIT: This Bogen manual has more info: http://www.bogen.com/support/discontinued/pdfs/MO100Am.pdf
It's really confusing as the Trannies can be paralleled on their primaries, secondaries or both. Or whole power amps can be "bridged".
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Thanks jjasilli, the Bogen manual cleared it up with one statement. The one where it says to bear in mind that paralleling the amplifiers reduces output impedance.
It seems to me that what they are talking about with the Bogens is essentially the same thing I'm doing which is connecting more than one output transformer secondary to the same speaker load.
Thanks again,
Dave
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http://www.el34world.com/Forum/index.php?topic=7260.msg64162;topicseen#msg64162
Not so long ago I paralleled a pair of OPT's and halved the load. Honestly I was much happier with 2 separate transformers driving 2 separate speakers set about 8' apart.
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Hope this can be of some interest
from the italian Bible of DIY Transformer
http://digilander.libero.it/giunchifabrizio/scarica.htm
http://digilander.libero.it/giunchifabrizio/_private/Manuale%20Trasfo%2001.pdf
http://digilander.libero.it/giunchifabrizio/_private/Manuale%20Trasfo%2002.pdf
http://digilander.libero.it/giunchifabrizio/_private/Secondari%20Multipli.pdf
Mr. Giunchi sometime ago give me news about the use of multiple OT for SE or PP
here the PP connection possibilities
Kagliostro
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Here the SE possibilities
Kagliostro
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And here the original file with a "little" math about OT
Kagliostro
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Hi there! I´m gonna "up" this topic with a practical question.
I have a bunch of PP transformers from old 50-60 gear.
Most of them are 6V6 and EL84 with single 4 ohm output.
i have some 8 ohm speakers to match with those transformer. You get the idea?
Is clear for me that i need a SERIES connection on secondaries to get those 8 ohm.
Now, i can wire primaries SERIES or PARALLEL.
My question is how much tubes should i use for each scenario.
Correct me if i´m wrong.
Primaries SERIES: 4 tubes in PP
Primaries PARALLEL: 2 tubes in PP
Secondaries will be the same for both (8 ohm).
Thanks in advance!
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Ciao David
before to say something I would like to know if the OT you recovered are for a pair of tubes in PP or for a quartet in PPP
Franco
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I have a bunch of PP transformers from old 50-60 gear.
Most of them are 6V6 and EL84 with single 4 ohm output.
i have some 8 ohm speakers to match with those transformer. ...
Then don't waste the transformers by connecting multiple transformers. Get 2x 8Ω speakers and put them in parallel for a 4Ω load.
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Then don't waste the transformers by connecting multiple transformers. Get 2x 8Ω speakers and put them in parallel for a 4Ω load.
yes
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Then don't waste the transformers by connecting multiple transformers. Get 2x 8Ω speakers and put them in parallel for a 4Ω load.
yes
For practical reasons i prefer 1x12 amps. I already have those transformers on hand.
If in some point i need a different configuration i just can split them again.
Beside all those reason, i will like to know just for learning.
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Ciao David
before to say something I would like to know if the OT you recovered are for a pair of tubes in PP or for a quartet in PPP
Franco
Both OT are for a pair of tubes in PP.
Thanks!
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Both OT are for a pair of tubes in PP
OK, so you can't use an 8 ohm speaker connected to the 4ohm winding because this will double the reflected impedance
think to a "standard" 4 x el84 tubes OT, it has 4Kohm primary impedance and if the output winding is 4ohm connecting an 8ohm
speaker will double the reflected impedance to 8Kohm good for a pair of tubes
but if the OT is a "standard" 2 x el84 tubes, it has 8Kohm primary impedance and you can't connect an 8ohm speaker to the 4Kohm winding
becouse the reflected impedance will rise to 16Kohm
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about the connection of a pair of transformers you can try the connection show in the images I posted, where you see the secondary winding in series, but the problem is to obtain a reflected impedance compatible with the kind of PP you want to use (with attention also to the max power that the OT can accept)
(http://www.el34world.com/Forum/index.php?action=dlattach;topic=8471.0;attach=12546;image)
(http://www.el34world.com/Forum/index.php?action=dlattach;topic=8471.0;attach=12551;image)
may be you can use 4 tubes and the OT with primary in parallel and secondary in series
if you have the way to breadboard a circuit you can give it a try and test if the result is acceptable for you
Franco
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ok. But if secondaries are in series, it is 8 ohm. isn´t?
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Two 8K:4, parallel primary, series secondary, gives one 4K:8.
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Then don't waste the transformers by connecting multiple transformers. Get 2x 8Ω speakers and put them in parallel for a 4Ω load.
For practical reasons i prefer 1x12 amps. I already have those transformers on hand.
8Ω 100w resistor, parallel with your 1x12 speaker.
Can it be done? Yes.
Is it worth doing? No.
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Two 8K:4, parallel primary, series secondary, gives one 4K:8.
ok. So, were with 4k it work with 2 tubes in PP, now i should wired that "new" transformer with 4 tubes.
thanks
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8Ω 100w resistor, parallel with your 1x12 speaker.
Can it be done? Yes.
Is it worth doing? No.
Correct me if i´m wrong, but the way you are saying, i`m wasting power.
BUT, paralleling primaries, i just made a bigger transformer from two small ones.
:dontknow:
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Correct me if i´m wrong, but the way you are saying, i`m wasting power.
No, I'm saying you're wasting iron and resources.
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ok, but the way i want to connect them will be similar to two mono PP amplifiers into one speaker.
I don´t see were iron is wasted with 4 tubes working. :dontknow:
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Two 8K:4, parallel primary, series secondary, gives one 4K:8.
ok. So, were with 4k it work with 2 tubes in PP, now i should wired that "new" transformer with 4 tubes.
thanks
silly me. :BangHead: i mean:
"So, were with 8k it work with 2 tubes in PP, now i should wired that "new" transformer with 4 tubes.
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Or you must find a pair of tubes that are happy with 4K load
but if you can find such a pair of tubes they must accord to the PT you have
K
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If you must use the transfomers in parallel, then yes, primaries parallel secondaries in series gives 4k:8, which you could use with 4x 6V6/EL84.
But now does it make sense to have twice the power feeding the 1x12 you wanted to use? If yes, then all is good. If no, you're back to providing the proper load by getting the speakers you need.
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ok. We agree now. :icon_biggrin:
i already have a use for that guy.
My brother get a Leslie speaker/amp. Is a solid state model and he ask me for a tube amp for it.
I´ll try the Leslie 125 power amp as inspiration. (schematic attached)
Is a single speaker model, so i think is a good option.
*Off-topic*
With all this OT transformer i have the matched power transformers. The sad thing is they are 110-120v.
I suppose that use them with primaries in series to get them working with 220-230v here in Spain is totally unsafe, isn´t?
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Or you must find a pair of tubes that are happy with 4K load
but if you can find such a pair of tubes they must accord to the PT you have
K
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Can it be a pair of 6L6?
http://www.hammondb3organ.net/schematics/leslie/125/125.gif (http://www.hammondb3organ.net/schematics/leslie/125/125.gif)
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With all this OT transformer i have the matched power transformers. The sad thing is they are 110-120v.
I suppose that use them with primaries in series to get them working with 220-230v here in Spain is totally unsafe, isn´t?
That's safe. Are you really considering two PTs and two OTs on a single chassis that will try to fit inside a Leslie cab? Wouldn't you rather have a proper set of iron than a back breaking kludge? Just because you 'can' do something doesn't always make good sense to do so.
And what about the Leslie? Doesn't it have a 120VAC motor? I suppose you could put two motors in series also. :icon_biggrin:
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:icon_biggrin:
i know, i know.... thats getting weird.
Anyone ready to trade TWO 110vac P.T. and TWO O.T. for ONE 220vac and ONE 6L6 PP O.T.?
:think1:
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Anyone ready to trade TWO 110vac P.T. and TWO O.T. for ONE 220vac and ONE 6L6 PP O.T.?
Now you're talking! :headbang:
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ok. i´m gonna put some pictures on the Buy-Sell-Trade section.
The problem could be the shipping costs, but maybe worth it.
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Be sure to mention what they came from. Link to a schematic if available.
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> primaries in series to get them working with 220
Two *identical* transformers, that "should" work.
Personally I would be very afraid of such a scheme. If "anything" went wrong, you could have a LOT of stinky smoke.
A friend of a friend of mine has a car which is part of a 1937 Chevy, part of a 1992 S-10 truck, part of a 1989 Caprice, and parts of other cars, tractors, and busted-tools found behind Jimmy's garage. Would I drive it? Yes, Jimmy did the main work. Would I use it to commute a long way to work EVERY day? Or even every Saturday night? Probably not; I ended up with a recent Honda for every-day reliability and simple repair.