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UTC output transformers LS-63

141.0.8.155

Posted on April 14, 2015 at 07:11:45
genelex
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Posts: 95
Joined: October 16, 2005



Hello , I have a pair of utc ls-63 opt and they were just tested in a pp 6v6 amp and are working at 300v b+
Do you think these old transformers:
1.Are still as good as new production stuff
2. Have you ever heard of UTC potted transformers failing given they are 60 years old
3. The data sheet says you could uses them for single ended 2a3
is this worth trying?
thanks

 

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RE: UTC output transformers LS-63, posted on April 14, 2015 at 09:00:24
Eli Duttman
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I would worry about new "iron" matching the old stuff's quality, not the other way around.

I certainly would try the UTC LS-63s with 2A3s. Given what seems to be good power handling capability, the comparatively higher power Sovtek 2A3s yield could make them an excellent purchase.

BTW, you can "breadboard" things at modest expense by using triode wired 6AV5s as your initial "finals". Remember, Sylvania internally trioded 6AV5s to fill a U.S. Govt. order for 6B4Gs. The 2A3 and 6B4G are electrically equivalent, except for filament voltage.


Eli D.

 

RE: UTC output transformers LS-63, posted on April 14, 2015 at 12:44:21
dave slagle
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I'll just address #3 because I find it very interesting. It is my understanding that the LS-63's are minimally gapped designs and this is the first time I have seen reference to a transformer manufacturer suggesting unbalanced DC current in what is traditionally considered a PP design.

This brings back to the surface the "john hogan" designs of years past where he took much abuse for daring to use those webster PP outputs for SE amplifiers and anyone who enjoyed the sound of those amps was lectured that they just liked the sound of distortion.

dave

 

RE: UTC output transformers LS-63, posted on April 14, 2015 at 13:17:32
Tre'
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Didn't you do some tests or simulations that showed a marked reduction in inductance?

And doesn't a lack of inductance leave the tube playing into a beach ball shaped load line?

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: UTC output transformers LS-63, posted on April 14, 2015 at 14:19:46
dave slagle
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A while back I measured a LS-63 at various amounts of end to end DC current and once you get past the initial hit it becomes interestingly linear. I have also noticed that the sudden reduction of Q is a precursor to saturation so interestingly enough, as you saturate the minimally gapped areas of the core the Q increases and becomes fairly linear.

As for the limited amount of inductance, I think a 2A3 @ 50ma can sound wonderful with 15ma of inductance.

dave

 

RE: UTC output transformers LS-63, posted on April 14, 2015 at 16:07:55
genelex
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Its sounds like I have 2 votes for giving them a try with se 2a3's
So I will let you know how it sounds. I have some good magnequest iron to compare them with.

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 07:27:27
Tre'
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"...so interestingly enough, as you saturate the minimally gapped areas of the core the Q increases and becomes fairly linear."

Because I really don't understand I have to ask, are you saying that the load line will not be a beach ball, only a slightly "rotated to the vertical" ellipse, because the inductance stays more or less the same as the current changes around the idle point?

And it's the changing reactance that causes the beach ball shaped load line shown by VoltSecond and if the inductance stays more or less the same (even though it's low) the load line doesn't turn to a nasty beach ball shape?

VoltSecond doesn't indicate a changing inductance as being the cause of the mis-shaped load line, just a low inductance.

I'm really ignorant here, please help me understand.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 08:32:00
mqracing
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Tre:

As the ratio of primary L to reflected R changes with frequency so does not the phase angle of the load line.

When L becomes significantly larger than the reflected R it has less and less effect on the load line.

When the impedance of the inductance equals the reflected R you will have a 45 degree phase angle. Just one of the sub-optimal results of this is that half of the power developed by the tube is sunk in the hidden reactive arm in parallel with the primary's reflected R.

MSL



Builder of MagneQuest & Peerless transformers since 1989

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 09:03:28
Tre'
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Yeah, I got all that but does the load line become a beach ball because the inductance is changing as the current is changing or because "...the magnetization current of the 27 H (fixed value of inductance) is driving the tube into cutoff"

I don't think "changing inductance" were part of VoltSecond's simulations.

"As the ratio of primary L to reflected R changes with frequency..."

VoltSecond only shows the load line at 31Hz.

I think the problems caused by both "changing reactance of the inductance because of changing frequency" and "changing inductance because of changing current levels" are "in addition to" the issue VoltSecond is showing.

Tre'


Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 10:22:32
hifipaul
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Using it for a SE 10 is interesting.

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 10:23:23
mqracing
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Trre:

Remember... even if the L stays steady... it is the impedance of the L in parallel with the reflected R that will determine the magnitude of the load that the tube sees...

and since the inductive reactance changes with frequency... the loadline is forever changing in terms of it's magnitude and therefore is NOT a line but is as you surmised in your earlier post is curved...

as the effective impedance changes so doesn't the phase angle... again, due to the complex impedances of the L in // the reflected R.

You want the impedance of the L to swamp (i.e., be much larger than) the reflected impedance from the secondary...

The url below shows how to calculate load impedances and phase angles.

MSL





Builder of MagneQuest & Peerless transformers since 1989

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 10:34:58
dave slagle
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The ellipse of the loadline opens up as the ratio of the two loads increases. See the attached pictures and explain to me how it is possible that a plate choke could possibly sound good at low or high frequencies?












 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 11:08:52
mqracing
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Hi David:

It would be interesting to calculate the AC and DC fluxes using the operating conditions you tested under.

Also would be interesting to see some square waves and to do some harmonic distortion tests of the transformer itself under the proposed operating points.

MSL



Builder of MagneQuest & Peerless transformers since 1989

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 11:28:44
Tre'
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Location: So. Cal.
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" If VS graph's only captured a single frequency it would have been represented as a "point"... the line is made by connecting the many points across a wider bandwidth."

No, VoltSecond's graph DOES capture a single frequency.

"Grid Drive +/- 50 volts 31.25Hz"

An AC input signal just changes the bias. The plate current and plate voltage then change following the load line. A single frequency is sufficient to represent the entire load line for that frequency.

My read of VoltSecond's article is that low inductance alone will cause a elliptical or beach ball shaped load line.

And the issue of the reactance changing with frequency, and the issue of the inductance changing with current are both "in addition to" the issue that VS is addressing.

Tre'


Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 12:03:24
mqracing
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Tre:

My error as re: the "single point"... that's why I had removed that text from an earlier post in a subsequent edit.

you wrote:

"My read of VoltSecond's article is that low inductance alone will cause a elliptical or beach ball shaped load line."

agreed if we add that it is the amounts of L relative to the reflected R that determines the shape of the load line.

Again... see the link I provided for "load lines and phase angles" in an earlier post.

It's not really that difficult... and if you think about it... it makes sense that the higher your nominal (reflected) primary impedance the more L you will need to support it.


you wrote:

"And the issue of the reactance changing with frequency, and the issue of the inductance changing with current are both "in addition to" the issue that VS is addressing."

reactance does change with frequency as in (two times pi times F times L).
Any change in frequency (while others remain constant) will yield a different inductive reactance. That's why it a reactance... the impedance changes with frequency if the L remains constant.

the "inductance changing with current"... yes, L will to a greater or lesser extent (depending on other more complex variables)change with drive level across the primary. But one of the keys is to make L so large (even at smaller drive levels) that it still swamps the reflected R in terms of magnitude.


MSL






Builder of MagneQuest & Peerless transformers since 1989

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 12:06:45
Tre'
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" See the attached pictures and explain to me how it is possible that a plate choke could possibly sound good at low.."

That was where I was going.

A gaped transformer (or plate choke) can't have near enough inductance (practically speaking) to allow for good performance at low frequencies.

My conclusion is to use SET amplifiers only for mid and high frequencies.

As for the high frequencies, can the shunt capacitance be held low, by the winder, if the transformer is not meant for LF duties?

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 12:59:12
Tre'
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OK Mike, I'm with you on all points.


"...are both "in addition to" the issue that VS is addressing."

But no one has addressed the issue that VS's article is about.

My read is that VS is talking about something separate from reactance changing with frequency and inductance change with current.

But all three lead me to believe that a gaped transformer is unfit for LF duties. There's just no way to get sufficient inductance with a gap.

Thank you for your input.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 13:37:50
mqracing
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Tre:

Here's two examples (assuming no math errors on my part) to reconsider your viewpoint.

If you have a 2500 ohm primary (this example is for series feed conventional airgapped single ended output)and 40 henries of pri L your power response will be down 3db at 10 hz.

If you have a 2500 ohm primary (this example is for series feed conventional airgapped single ended output) and 20 henries of pri L your power response will be down 3db at 20 hz.


Power response is -3db when the inductive reactance equals the reflected pri impedance.


And here's a parafeed example I just did using VoltSec's parafeed calculator.

Rp 800 ohms
Rload 2500 ohms
pri DCR 125 ohms
pri L 250H
Cparafeed 5uf
L plate choke 40H
R plate choke 325 ohms

No output ringing/peaking

-3db large signal @ 5.8 hz





Builder of MagneQuest & Peerless transformers since 1989

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 14:09:39
Tre'
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"Power response is -3db when the inductive reactance equals the reflected pri impedance."

Yes, but how elliptical is the load line and what does that do in terms of the distortion?


Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 14:14:20
mqracing
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when the large signal (power response)is -3db the phase angle of the composite load impedance will be 45 degrees.

But keep in mind that the -3db is at 20 hz, 10 hz or 6 hz. How much program material do you have that dip down that low?

What would be the distortion from your speakers at the stated half power at these low frequencies?

MSL



Builder of MagneQuest & Peerless transformers since 1989

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 14:57:27
Tre'
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"It does not matter if your speaker does not go down to 31.25 Hz or not. If you are sending low frequency information to the amplifier, the amplifier will make the plate voltage move. If the plate voltage moves, the tube must spend bias current to charge and discharge the primary inductance as well as the actual primary load impedance. If the plate voltage or current "clips" because of low frequency plate excursions, [all] the sound will suffer."

I already bi-amp at 200Hz. My mid speaker doesn't play very well below 200Hz. After reading VS's article I placed a cap (a high pass filter) in series with the input to the SET amp. The sound, all the sound, got much better.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 15:05:29
mqracing
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Tre.

I largely agree with you as regards taking steps to exclude frequencies that an amp is not designed nor capable of handling well.

I remember back in the eighties Frank Van Alstine designed such an input for his ST-70 mods... to my ears the amp sounded better with the filter than without. But that may not have been due to power handling issues either alone or in concert with other performance issues...

I just read about a week ago... his newly produced ST-70 offerings still use an input filter... and if I recall correctly the -3db points are 5 hz and 50khz.

But in terms of low freq cutoff point for the large signal model... the -3db frequencies demonstrated are pretty darn low...

again... what source material is going to have recorded data at these frequencies?

Seems like we are chasing ghosts a bit here...

MSL



Builder of MagneQuest & Peerless transformers since 1989

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 15:09:57
Tre'
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"Seems like we are chasing ghosts a bit here..."

That could be but limiting the LF of my SET made a huge subjective improvement.

I think VS answers why in the section of his article "How does the low frequency load line affect the high frequencies?"

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

and you know what is weird in it's own way?, posted on April 15, 2015 at 15:12:09
mqracing
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you were saying your prefer solid state amps for low end duties...

but what strikes me is that many solid state amps have the functional characteristic of delivering less power as the secondary's load impedance increases...

how many times do you see Sand State M10,000 delivers X number of watts into four ohms but only half of X into eight ohms...

just goes to show that after a 100 years of tubes and sixty plus years of sand... we've still not achieved technical nirvana.

But things can sound damn, damn good and I still enjoy listening to music.

MSL



Builder of MagneQuest & Peerless transformers since 1989

 

RE: and you know what is weird in it's own way?, posted on April 15, 2015 at 15:48:42
Tre'
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".......I still enjoy listening to music."

So do I.

From the old TV commercial, "Nothing's perfect Ma'am"

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: and you know what is weird in it's own way?, posted on April 15, 2015 at 17:46:08
Triode_Kingdom
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"how many times do you see Sand State M10,000 delivers X number of watts into four ohms but only half of X into eight ohms..."

Mikey, that's just Ohm's Law. A solid state amp is a voltage source, and it's maximum output swing is strictly limited by the power supply. Apply an identical voltage to two resistors, and the larger value resistor draws less current. Less current - for the same voltage - dissipates less power in the load.

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 20:18:12
dave slagle
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Lets look at the case of 100hz with a reasonable (50hy) amount of inductance. Granted the 5K load is a bit harsh for a 211 but it does have the narrowest ellipse and the 1Meg load (ie a plate choke) has the widest which makes me wonder if the width of the ellipse actually matters?

It is interesting to note that the Red does have the lowest current swing at 40ma, the Blue roughly double that at 80ma and the green swings 120ma of current.

I'll run some transients and see what the FFT says...

dave

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 20:43:00
Caucasian Blackplate
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It's SUPER hard to make a gapped SET output transformer with sufficient inductance, while at the same time not throwing in the towel on everything else (bandwidth issues at the other end). (See the thread a month or two ago regarding the $$ Hashimoto 2.5K OPT's with 13H of primary inductance)

Parallel feed really eases up these tensions, and is something good to consider for bass duties. If your wallet is pliable, you can realistically achieve 50H for your 2.5K output, so you're really only left with damping considerations.

Unfortunately, the only good SET gapped output transformers that I have (DS-025 naturally) are built into a stereo SET that required a bit of global feedback, so measurements there won't be helpful.

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 20:47:32
dave slagle
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OK... here is the transient behavior for the loadlines above...





as expected, the lightest load shows the most gain and interestingly enough, it also has the lowest distortion. Now for the FFT...





I'm not sure why we have a color shift between the 5K and 16K in the FFT but here are the data points..


Direct Newton iteration for .op point succeeded.
Fourier components of V(out_16k)
DC component:0.000594292

Harmonic Normalized
Number Component
1 1.000e+00
2 1.100e-02
3 1.283e-03
4 1.987e-04
5 3.711e-05
6 6.282e-06
7 2.107e-06
8 3.145e-07
9 6.095e-07
Total Harmonic Distortion: 1.107250%


Fourier components of V(out_5k)
DC component:0.000168459

Harmonic Normalized
Number Component
1 1.000e+00
2 4.851e-02
3 1.028e-02
4 3.092e-03
5 1.113e-03
6 4.449e-04
7 1.920e-04
8 8.767e-05
9 4.107e-05
Total Harmonic Distortion: 4.970236%


Fourier components of V(out_1meg)
DC component:0.0011142

Harmonic Normalized
Number Component
1 1.000e+00
2 3.483e-03
3 2.584e-04
4 2.581e-05
5 4.752e-06
6 5.223e-07
7 7.718e-07
8 6.762e-07
9 5.302e-07
Total Harmonic Distortion: 0.349257%


Date: Wed Apr 15 23:30:12 2015
Total elapsed time: 13.688 seconds.

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 20:55:25
dave slagle
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to keep things in perspective here is the FFT lowering the input on the 16K and 1 meg versions to normalize the fundamental.

 

RE: UTC output transformers LS-63, posted on April 15, 2015 at 21:01:45
dave slagle
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finally, dropping the frequency down to 25hz nets the following distortions...

Circuit: * C:\Documents and Settings\Administrator\Desktop\LTspice\distortion 211.asc

Direct Newton iteration for .op point succeeded.
Fourier components of V(out_16k)
DC component:0.00186278

Harmonic Normalized
Number Component
1 1.000e+00
2 3.012e-02
3 4.780e-03
4 1.021e-03
5 2.522e-04
6 6.747e-05
7 1.962e-05
8 5.763e-06
9 1.720e-06
Total Harmonic Distortion: 3.051666%


Fourier components of V(out_5k)
DC component:0.00130548

Harmonic Normalized
Number Component
1 1.000e+00
2 7.082e-02
3 1.922e-02
4 7.692e-03
5 3.789e-03
6 2.130e-03
7 1.315e-03
8 8.702e-04
9 6.071e-04
Total Harmonic Distortion: 7.392847%


Fourier components of V(out_1meg)
DC component:0.00186514

Harmonic Normalized
Number Component
1 1.000e+00
2 2.851e-02
3 4.465e-03
4 9.272e-04
5 2.188e-04
6 5.791e-05
7 1.497e-05
8 4.934e-06
9 1.482e-06
Total Harmonic Distortion: 2.887076%


Date: Wed Apr 15 23:59:57 2015
Total elapsed time: 3.969 seconds.

tnom = 27
temp = 27
method = modified trap
totiter = 109323
traniter = 109319
tranpoints = 25692
accept = 19265
rejected = 6427
trancuriters = 0
matrix size = 33
fillins = 6
solver = Normal

 

and the tube amp..., posted on April 16, 2015 at 04:14:25
PakProtector
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Posts: 12356
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with its multi-tap secondary applies more voltage to the larger load...:)

The other side of that SS example is that when the load is halved power doubles( assuming its PS can deliver the current ). So, n Kw into 8R leaves you with 2n into 4R, and 4n into 2r...and of course n/2 into 2R.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: UTC output transformers LS-63, posted on April 16, 2015 at 07:46:05
Tre'
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That's interesting.

Isn't the width of the ellipse the indicator of the ratio, reflected//reactance, with the power into the reactance not going to the intended load, not only wasted but causing harm?


Can you do the same for a 2a3 at 15Hy and 2500 ohms and 31Hz for the LS-63 wired for 2500 ohms?

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: UTC output transformers LS-63, posted on April 16, 2015 at 09:16:00
dave slagle
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There seems to be some confusion on what the inductance does. A pure inductance does not consume power, it merely draws it at a different point in time and then releases it back into the load (viewed by the opening of the ellipse). This becomes an issue when the current required by the inductance / load combo puts the source into current clipping / current cutoff. Like any other load line it also becomes problematic when it enters the nonlinear area of the tube curves but in the case of a fixed inductance and decreased load, the total current swing goes down keeping you further away from the non-linear areas.

Putting it another way, I believe the load provided by the inductance to the source is fixed and by decreasing the reflected load you actually allow the source more available current to better deal with the reactive nature of the inductance.

dave

 

RE: UTC output transformers LS-63, posted on April 16, 2015 at 09:38:19
mqracing
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the primary inductance (self inductance) of the output transformer is in parallel with the reflected primary impedance which is the product of the turns ratio squared times the load resistance on the secondary winding.

the current consumed by the primary inductance does not contribute to power reaching the secondary. It is a shunt arm.

that's why your power response (large signal response) will be down -3db when the inductive impedance of the primary equals the reflected impedance. One half of the power is diverted from the secondary load.

in the output stage the only generator we have available is the anode of the tube. It must be capable of providing the vector sum of the necessary AC signal current as well as the current consumed by the shunt arm i.e. the inductive reactance.


the exciting current can be calculated from;

Iex = Ep divided by (two times pi times F times L)


MSL





Builder of MagneQuest & Peerless transformers since 1989

 

RE: UTC output transformers LS-63, posted on April 16, 2015 at 09:50:42
mqracing
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Tre:

Here's some quick calcs for the quantities you listed;

15H
2500 ohms
31 hz

the phase angle is 40.55 degrees


the -3db large signal (power response) will be at 26.5 hertz

your actual signal losses will be greater than -3db as we've not included any copper losses nor any core losses.

MSL


MSL






Builder of MagneQuest & Peerless transformers since 1989

 

RE: UTC output transformers LS-63, posted on April 16, 2015 at 10:07:30
dave slagle
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Requested Sim... I'm not totally offended by this since in order to get a full scale signal at 30hz, the levels at higher frequencies will surely be much more of an issue.

Ultimately If I had the LS-63's I'd give it a shot but I don't think I would go on an ebay hunt to try it out.





 

some current calculations using your example..., posted on April 16, 2015 at 11:40:38
mqracing
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Assume use of 2A3 tube which develops 3 watts of output power per published ideal design parameters.

pri impedance 2500 ohms

AC signal volts (full power) will be 86.6 vrms

AC signal current .0346 Arms


now let's calculate and then add in vectorially the currents wrought by the inductive reactance of the primary;

using the 15 henries that you spec'd @ 31 hz and full power (86.6 vrms) we would have;

Iex .0296 Arms

Itot .0458 Arms (vector sum)

notice that our total current draw is 132% greater than the signal current.


Now let's keep all the same parameters but reduce the freq to 26.5 hz.
this is the -3db large signal point. It is where the inductive reactance equals the reflected impedance.

Heres the resulting current draws;

Iex .0346 arms

I total .049 (142% greater than the signal current)

also note that the Iex equals the Iac signal current. This is because we are delivering half of our power into the shunt arm (the inductive reactance) hence the currents btwn the two "circuits" are the same value.

but now the 2A3 must work (from the current standpoint) 142% harder to drive the complex reactive loadline that the anode of the tube is looking into.

And, again, real world losses will be even greater than shown above since we are not accounting for any copper losses (remember we are now shoving 142% more current through the copper circuit) or core losses.

Not an entirely pretty picture.

MSL





Builder of MagneQuest & Peerless transformers since 1989

 

RE: UTC output transformers LS-63, posted on April 16, 2015 at 11:48:59
mqracing
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It would be interesting and instructive to see the same graphs but with the inductance doubled and tripled....

and see how quickly the ellipses collapse...

L is your friend....

MSL



Builder of MagneQuest & Peerless transformers since 1989

 

RE: UTC output transformers LS-63, posted on April 16, 2015 at 12:09:45
mqracing
Manufacturer

Posts: 4323
Joined: June 29, 2000

Dave wrote:

"Ultimately If I had the LS-63's I'd give it a shot but I don't think I would go on an ebay hunt to try it out."


this trans is just begging to be parafed. It would excel at least in terms of it's magnetic curcuit behaviour.

You'd have the full complement of the (as advertised) 275H not the diminished 15 or 20 henries after applying the dc (unbal) plate current
as per your graph.

From the vantage point of flux density... with the AC flux and dc flux added together I would guess that this unit is probably getting close to the "redline"...

now remove the dc flux component and we have 86.6 volts across the primary... we will have tons and tons of magnetic headroom... the core will be loafing....

I did a quickie sim (posted earlier) using VoltSec's parafeed caculator;

Rp 800 ohms
Rload 2500 ohms
pri DCR 125 ohms
pri L 250H
Cparafeed 5uf
L plate choke 40H
R plate choke 325 ohms

No output ringing/peaking

-3db large signal @ 5.8 hz

compare that to the -3db point of 26.5 hz using Tre's series fed example. The parafeed will go two plus octaves lower (for -3db point) than the series fed example.

And even if we're not in need of a low freq power response down to six or so hertz... the advantage is that one, two, three and so on octaves above the six hertz will benefit from lower stress and less work for the output tube... it's a win, win.


my only caveat is that push-pull transformers are designed (the better ones anyway) with the push and pull halves of the primary being mirror images of each other in terms of coil geometry...

if you use a PP trans single ended you "upset" the voltage and capacitive gradients that the trans was designed for...

designing a single ended output as a dedicated SE trans... your coil design and the variables of that process can be moreso optimized for this type of operation.

But I'd go parafeed in a heartbeat vis-a-vis using this PP trans in a conventional series fed circuit.

MSL




Builder of MagneQuest & Peerless transformers since 1989

 

RE: UTC output transformers LS-63, posted on April 16, 2015 at 13:29:54
dave slagle
Manufacturer

Posts: 5429
Location: NYC
Joined: April 27, 2001



OK...
Green 15hy
Blue 30hy
Red 60hy.

Of course L is your friend... however it doesn't come for free and I find the baggage that comes with obtaining lots of it is often not a good tradeoff.

 

RE: UTC output transformers LS-63, posted on April 16, 2015 at 13:52:51
Tre'
Industry Professional

Posts: 17263
Location: So. Cal.
Joined: February 9, 2002
But we can accomplish the same by limiting the LF we ask the transformer to handle.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: UTC output transformers LS-63, posted on April 16, 2015 at 14:49:08
mqracing
Manufacturer

Posts: 4323
Joined: June 29, 2000
Hi Tre:

Even with use of an input filter to limit low freq response... say you use a filter for 50 hertz... you may have dug yourself out of the worse of the misbehaviour but...

none-the-less at frequencies above this... say at 100 hertz or 200 hertz... the larger inductances are going to have narrower ellipsis (i.e., a less reactive load line) than the smaller inductances...

so there is still benefit to having more as opposed to less L.

Go back and read VoltSec's article... doing this a bit from memory.... but one of the things VoltSec showed was that even two decades above the lowest frequency shown (31.25 hz) there were still discernible differences in the loadlines at 3125 hertz due to the lower primary inductances (27H IIRC).

MSL




Builder of MagneQuest & Peerless transformers since 1989

 

Thank you Dave!!!, posted on April 16, 2015 at 14:49:56
mqracing
Manufacturer

Posts: 4323
Joined: June 29, 2000
nt



Builder of MagneQuest & Peerless transformers since 1989

 

quick question...., posted on April 16, 2015 at 14:59:10
mqracing
Manufacturer

Posts: 4323
Joined: June 29, 2000
why are there multiple traces\loops for each color/example?

MSL



Builder of MagneQuest & Peerless transformers since 1989

 

RE: quick question...., posted on April 16, 2015 at 15:30:21
dave slagle
Manufacturer

Posts: 5429
Location: NYC
Joined: April 27, 2001
They were done using a LT spice simulation by Stephie Bench and I have it set to run 20 cycles for it to stabilize. I'm sure if you configured it to run 20 cycles then sample one it would be much "cleaner"

dave

 

RE: UTC output transformers LS-63, posted on April 16, 2015 at 15:49:29
Tre'
Industry Professional

Posts: 17263
Location: So. Cal.
Joined: February 9, 2002
I think you missed VS's point.

He was running 31.25Hz and 3125Hz at the same time and then filtering out the 31.25Hz at the output to show the IMD at 3125Hz.

If you filter out the 31.25Hz before the OPT then the IMD never happens.

"How does the low frequency load line affect the high frequencies?

As the load line varies, the tube characteristics (gain) will vary. This variation causes intermodulation distortion (IMD). To keep this example reasonable, the grid drive was set to be +/ - 25V at 31.25 Hz and +/ - 25 V at 3125 Hz. This results in a +/ - 50 V waveform at the grid of the 2A3 which is the same as what we had at just 31.25 Hz.

To see the effects of the variation in tube gain I put a buffered filter on the load to strip out the 31.25 Hz.

With 27 H, the 3125 Hz waveform is modulated by the 31.25 Hz signal. The 3125 Hz signal varies from 246.6 V peak to 225.9 V peak or 20.7 V peak to peak modulation"

BTW I use a simple 6db per octave high pass filter at 130Hz at the input of my SET amps. The idea is to keep the tube from ever traversing the nasty LF load line.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: UTC output transformers LS-63, posted on April 17, 2015 at 13:20:07
hennfarm
Audiophile

Posts: 535
Location: Oregon
Joined: October 8, 2008
Very informative thread. Thanks guys.

 

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