OT specs and what the mean

[Ed_Chambley]

I have an output transformer which says 4900 ohms primary and has a single 8 ohm tap.  What could this transformer be used for?  How do you determine that?

[RicharD]

That is the impedance ratio.  It is calculated by turns ratio squared times the load.  Turns ratio equals voltage ratio which can be measured by injecting a small ac signal.  You also need to know the va or power rating to determine what it can safely be used for.

[Ed_Chambley]

the other info on it

Class B
E1205868(S)
130 CW

[Ed_Chambley]

I found out where it came from.  It came ou of a Supro Thunderbolt, 2. 6L6 or 5881.  I guess 40 watts or so.  My question is can you use a larger OT for smaller tube.  Would it be ok to use this in a 2 6v6 or a 2 el84 build?  It si a nice transformer as it is a Mercury Magnetics, the model tag is scraped where you cannot read it anymore.

[punkykatt]

I don`t see why not. Just connect a 16 ohm load to the 8 ohm secondary for a better Z match.

[RicharD]

There's an excellent thread from a few months ago where PRR explains designing output stages.  Pester me later on and I'll see if I can help locate.

That transformer could be used with other the tubes you mentioned but it's not really ideal.  There are tricks to change the reflected impedance or you can bias for a heavier load.  A lower power output tube may not saturate the transformer satisfactorily.  Start exploring tube data sheets.  If you look at the cut sheet for the 6L6GC http://www.mif.pg.gda.pl/homepages/frank/sheets/093/6/6L6GC.pdf on page 2 at the bottom, Push Pull class AB1,  you'll note 5k is right in line with the listed effective load resistance plate to plate.  Now look at the 6V6 cut sheet.  http://www.mif.pg.gda.pl/homepages/frank/sheets/135/6/6V6GTA.pdf  Rl is roughly double but the given B+ is much less.  That should be enough information to seriously confuse you. :P  Lemme look for that thread.  

[DummyLoad]

boilerhousing... about 4-6W per pound of weight for push-pull types up to around 100W then closer to 10W per pound beyond that. around half that for SE types.

guitar amps don't need the low frequency response that HI-FI or bass guitar does, so they'll typically weigh in less for the same wattage rating as HI-FI or bass OT.

a pic for reference - one is 100W bass (left) OT the other is 100W guitar (right) amp OT.

--DL

[HotBluePlates]

My question is can you use a larger OT for smaller tube.

You can, but why waste a big lump of iron on a few watts?

That question matters more if you're buying, vs already have the OT on hand.

[Ed_Chambley]

My question is can you use a larger OT for smaller tube.

You can, but why waste a big lump of iron on a few watts?

That question matters more if you're buying, vs already have the OT on hand.

I have it already.  What I have is a Hammond 270FX PT (270FX, 138VA, 115 VAC, 60 Hz, 550V C.T. @ 173ma., 5V @ 3A, 6.3V C.T. @ 5A) and this OT which is a SUP-TH-O Mercury Magnetics.   I emailed them and they sent back It is a 4900 primary and 8 ohm secondary.  I have no money invested in either of these.  I am building a Bassman currently, so I am planning my next build.

Stuckey and Doug have helped me with a AB763 lite turrent board (no verb or trem).  I would like to make an el84 amp since I have many 6L6's and EL-34's and 6V6.  I was wondering if I could use this iron to do it since I have no money invested.  Also since the PT has no bias tap, I would like to make it cathode bias.  So now I am trying to learn about OT's and also PT's and I will have a lot of questions.  Like the PT's Secondary stated 550v, does that mean I will have 275-0-275 ACV on each which to some of what I have read is good for el84's.  I am probably waaay off base here, but I gotta start somewhere.  Also, reading tube datasheets some of the thing I do not understand.  A Phillips el-84 has a Zout of 5,200 Class A, SE.  I am assuming that is the impedance?  If you use 2 tubes, does the impedance double or stay the same?  I see it can be wasteful as this OT could probably run 4, EL-84's in Push-Pull for much more wattage as in an AC-30.

I am sure I am confusing lots of things here, but any explanation would be appreciated.

[sluckey]

Stuckey and Doug

It's not Stuckey! That's a nik-nak store on the interstate system in the south. It's Sluckey, short for Steve Luckey (first initial, last name).

I gave you lots of options for that PT and EL84 amps a couple weeks ago. Just because it doesn't have a bias tap does not mean you can't use it in a fixed bias amp. Please revisit that thread.

I personally would not use that OT on a EL84 amp, but it will certainly work. You may not get a maximum power transfer but so what. These days most builders are trying to figure out how to build a quieter amp anyway.

Quit thinking about SE design with that OT.

[Ed_Chambley]

Stuckey and Doug

It's not Stuckey! That's a nik-nak store on the interstate system in the south. It's Sluckey, short for Steve Luckey (first initial, last name).

I gave you lots of options for that PT and EL84 amps a couple weeks ago. Just because it doesn't have a bias tap does not mean you can't use it in a fixed bias amp. Please revisit that thread.

I personally would not use that OT on a EL84 amp, but it will certainly work. You may not get a maximum power transfer but so what. These days most builders are trying to figure out how to build a quieter amp anyway.

Quit thinking about SE design with that OT.

I did not forget about the suggestions for the PT.  Sorry I got your name wrong.  I am trying to understand the OT and what impedance has to do with anything.  It is easy to build a kit or to be spoon-fed.  You told me the PT was about perfect for a PP el-84.  Then you mentioned a Stout, November, matchless etc.

Now Sluckey (they have great pecan rolls as well) why would you not use the OT for a single ended amp?  I could simply order the 18 watt transformer Doug sells, but I would not know why you would not use the transformer I already have.  So I have learned to order something, but I still know nothing about the differences between the 2 and why one is better suited to EL-84's and why I should quit thinkijng about that OT for a single ended amp.

[sluckey]

I've spent a lot of time in Stuckey's. My oldest daughter preferred Stuckey's to Disney when she was young.

I would not know why you would not use the transformer I already have

I personally would not use it because the impedance ratio is not optimum to match EL84s to common speaker impedances. It'll work, but someone designed that OT with 6L6s in mind. I can afford to buy a better suited OT for EL84s and just tuck that one away for another amp.

why I should quit thinkijng about that OT for a single ended amp.

Because it was manufactured for a push pull amp. It's not a matter of different tubes, but different circuits. There's a big difference between the construction and physical requirements of P/P OTs and SE OTs.

http://www.freewebs.com/valvewizard/index.html

[Ed_Chambley]

I've spent a lot of time in Stuckey's. My oldest daughter preferred Stuckey's to Disney when she was young.

I would not know why you would not use the transformer I already have

I personally would not use it because the impedance ratio is not optimum to match EL84s to common speaker impedances. It'll work, but someone designed that OT with 6L6s in mind. I can afford to buy a better suited OT for EL84s and just tuck that one away for another amp.

why I should quit thinkijng about that OT for a single ended amp.

Because it was manufactured for a push pull amp. It's not a matter of different tubes, but different circuits. There's a big difference between the construction and physical requirements of P/P OTs and SE OTs.

http://www.freewebs.com/valvewizard/index.html

Truthfully, I can afford to buy whatever parts I want.  Money is not the reason for my questions.  I have been reading the valve wizard many times.  Looking at tube data sheets, they give listings for impedance per usage.  PP, SE, A, AB, AB1 and whatnot.  How can you tell by the specs that the OT is designed for 6L6's.  The tube datasheet for 6l6's states 5000ohms at 275 volts.  Is that why.  Also on the PT the secondary states 550VAC, where does the other readings I see like 300-0-300VAC come from?

[tubeswell]

That 5k PrZ OT is good for 2 x 6L6 cathode biased, just like the Supro T-bolt (of any one of several Supro cathode-biased 6L6 PP amps), or a Fender 5D4 Super, or 5D5 Pro, etc

[sluckey]

Money is not the reason for my questions.

I know that. I was not implying that you are broke. But you asked why I would not use it and money is part of the reason that I would not use that OT for a EL84 amp. If I had no money I probably would use it, especially since it would never be used outside my house.

How can you tell by the specs that the OT is designed for 6L6's.

I didn't look at any spec sheets. I went strictly by what you said, "this OT which is a SUP-TH-O Mercury Magnetics.   I emailed them and they sent back It is a 4900 primary and 8 ohm secondary.". That Supro Thunderbolt is a popular 6L6 amp. Mercury Magnetics makes quality (but pricey) stuff. I trust they got it right. Also, from my cyber experience, I've learned that a lot of 6L6 amps use 4300 ohm OTs. 4900 is close enough to say it's good for 6L6s.

Go to Hammonds website and look at their OTs for tube amps. Look at their specs. After a while, you'll just remember some of these specs. I'm a practical, fixer type person and don't mind plagerizing.

Also on the PT the secondary states 550VAC, where does the other readings I see like 300-0-300VAC come from?

550VAC is the voltage across the entire secondary (measuring end to end). But that PT has a center tap. If you measure voltage between either end and the center tap, you'll get half of 550VAC, or 275VAC. So, you may see that PT listed as 550VAC w/CT, or you may see it listed as 275-0-275. It's all the same.

[Ed_Chambley]

Read Valve Wizard again on PP and SE.  It is beginning to make sense.  It all begins at tube selection and then the proper power to drive the tubes.  That is why you said the PT I have is good for EL-34's. as it is 275-0-275.  Now the OT I have is going to be underdriven.  Kind of like thinking if you put a bigger carburetor on a car it will run faster when in fact it will do the opposite.  So the OT is too much for EL-34's and they will not be able to provide enough voltage to get the transformer responding as it was designed.  Therefore lower output.

[PRR]

> el-84 has a Zout of 5,200 Class A, SE.  I am assuming that is the impedance?

It is not the TUBE impedance. It is a happy LOAD impedance, FOR the specified supply voltage and current. If you have higher voltage and lower current, you would use a higher load impedance.

SE is fairly easy. Assume G2 voltage will be similar to plate voltage. Find the tube's "triode plate resistance", double that, this is about the lowest load impedance it will work well at. To make the most of the tube, you want to run 100% of rated plate dissipation. Use Pdiss and supply voltage to get proper current. Divide voltage by current, that's roughly a good load impedance. Note that higher voltage does not mean higher power; stay above the minimum happy load (2*Rp{triode}) then just hit your Pdiss limit, that's as good as it gets for Power Output. Pout will approach 40% of Pdiss.

Push-Pull self-bias is a little harder. Again you want 100% Pdiss, use supply voltage to get current. V/I is the load on the power supply. Double that for a happy load impedance. Pout can exceed 50% of Pdiss.

Push-Pull fixed-bias opens MANY more variables.

[PRR]

> why would you not use the OT for a single ended amp?

Bicycles are made for 2-legged riders.

I have seen a 1-legged bicycle rider. There is enough momentum to carry the bike through the missing stroke, on the level.... but ramps were tough.

It might be better with a heavy flywheel on the crank. The first OOMPH would be hard work, but the stored energy would carry-over the missing leg-stoke better.

Audio swings both ways. One tube alone can only swing one way.

SE transformers "must" be built with extra iron for extra energy storage, to carry-over the "other way" half-cycle. When you first turn-on, the first 40mA of current charges-up the iron. Then the tube swings up to 80mA and down to zero. The result is +/-40mA output.

[Ed_Chambley]

What is rthe biggest watt SE amp you ever heard.  Amps like the old champs sound so good, I have always been interested in what a high watt SE would sound like.

[HotBluePlates]

Amps like the Champ sound good because you're cranking the snot out of them, and your ears don't hurt.

The gap between SE and push-pull narrows when you compare smallish push-pull to big SE. The gap is narrowed even further if you leave negative feedback off the push-pull amp, and have some way to slightly unbalance the phase inverter output.

[sluckey]

That is why you said the PT I have is good for EL-34's. as it is 275-0-275.

I never said that in this thread or your other thread about this PT.

So the OT is too much for EL-34's

Probably work better with EL34s than EL84s.

[RicharD]

http://www.el34world.com/Forum/index.php?topic=12495.msg116468#msg116468

In this thread, PRR explains in some detail designing an output stage.  Output stage designing is more difficult than preamp designing.  I would suggest grasping that first..... well power supply designs before that.  Richard Kuehnel has written several excellent books.  I highly recommend the reading.

[Ed_Chambley]

That is why you said the PT I have is good for EL-34's. as it is 275-0-275.

I never said that in this thread or your other thread about this PT.

So the OT is too much for EL-34's

Probably work better with EL34s than EL84s.

Stated the EL-34 thinking El-84.  I am confusing my 84's with 34's.  What I meant to write is the OT is too much for EL-84's.  Also, I know you never stated exactly what I wrote, I am confusing 34's and 84's.  What you did say is the PT is good for EL-84's.  My mistake.  I knew what I meant, don't know why you didn't.   So basically what I have is a PT good for PP EL84 and an OT for 6L6. I acquired this stuff in a box along with other parts from a guy who was planning a build with all the parts in the box.  Now I am wondering what he was planning since these 2 transformers don't seem to work together unless you wanted to build a low voltage 6L6 of some sort.  It had the tubes, JJ 6l6 and a 5Ar4 and 2, 7199's.

[John]

He mighta been a guy like me, collecting cheap parts with no idea of what he was gonna do. 

[sluckey]

Now that you're getting the points I was so poorly trying to make, I'll throw in some mud.  

That PT could be used with a variety of different tubes. It would work well for 6V6s or even a pair of 6L6s if you keep the power down to about 25-30 watts. And there's a ton of SE amps that would like that PT.

And the OT has an impedance ratio of 4900:8. That's the same as 2450:4, or 9800:16. You really need to stick with a push pull amp with this OT, but there are many possible applications IF you are not concerned with maximum power transfer.

And the PT and OT might be a good combination for that Supro Thunderbolt.

[Ed_Chambley]

He mighta been a guy like me, collecting cheap parts with no idea of what he was gonna do. 

It would make much more sense to have 5881's and GZ34 and sovtek 12ax7-wa.  Better use for the lower wattage.

[Ed_Chambley]

Now that you're getting the points I was so poorly trying to make, I'll throw in some mud.  

That PT could be used with a variety of different tubes. It would work well for 6V6s or even a pair of 6L6s if you keep the power down to about 25-30 watts. And there's a ton of SE amps that would like that PT.

And the OT has an impedance ratio of 4900:8. That's the same as 2450:4, or 9800:16. You really need to stick with a push pull amp with this OT, but there are many possible applications IF you are not concerned with maximum power transfer.

And the PT and OT might be a good combination for that Supro Thunderbolt.

Tou know way more about this stuff than me, but I think you are grasping at straws with this comment.  Maybe with an extremely efficient 15 inch speaker, but getting any high seem like it would be impossible.  When I saw the reply from Mercury, that is where my mind went as it is a very cool amp, but I think you would have to feed it with an eq maxed out o the highs.  Icepick from hell as fmy calculations come up with.  Am I missing something?  A Thunderbolt is a great amp as I have played one before  I don't think this setup would get the zepplin 1 sound.