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In Reply to: RE: UTC output transformers LS-63 posted by Tre' on April 16, 2015 at 07:46:05
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.
Follow Ups:
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 ohmsNo 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
Edits: 04/16/15 04/16/15 04/16/15 04/16/15 04/16/15
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
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.
why are there multiple traces\loops for each color/example?
MSL
Builder of MagneQuest & Peerless transformers since 1989
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
nt
Builder of MagneQuest & Peerless transformers since 1989
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"
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
Edits: 04/16/15
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"
Edits: 04/16/15
Very informative thread. Thanks guys.
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