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Old 25th November 2008, 07:32 PM   #1
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Default Utc Ls-33

Folks,

Does anyone have the max primary current spec for the UTC LS-33 matching transformer?

TIA,

-- josť k.
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Old 25th November 2008, 07:55 PM   #2
kmaier is offline kmaier  United States
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The LS-33 is for high-level line matching... not intended for a DC current in the primary but has a 20-watt rating. Here's a link to the spec sheet:

http://www.bunkerofdoom.com/xfm/UTC_1970_WEB/023.jpg

Regards, KM
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Old 25th November 2008, 08:06 PM   #3
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According to two catalogs I have (TRW/UTC & an old Radio Master) this is a high level line matching transformer with multiple low impedance primary and secondary. (600 ohm max) No primary DC current is specified either balanced or unbalanced. I think it is designed for AC only and assumed there will be no DC componet. With a 20 watt max level perhaps a few well balanced milliamps could be tolerated.

Victor
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Old 26th November 2008, 01:10 AM   #4
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The LS-33 is designed for matching a 50-500 ohm PA line
to another line or down to voice coil. The primary was intended
to be connected to another transformer, so there's no intentional
DC tolerance built in as far as I know.

I have one on the bench now for measurement because I thought
it might be useful as an interstage transformer. What I've concluded
is that it needs to be driven by 200 ohms or less impedance. The
primary inductance is only about 18H. Less than 100 ohms would be
ideal. The DCR with the 500 ohm connection is 46.5 ohms.

Since it's built for 20 watts, the primary will take some current,
heat-wise. 20 watts is 100V RMS into 500 ohms, which gives
200mA RMS signal current in the primary. Maybe if the DC is
balanced perfectly you could get away with some kind of push-pull.

I've decided to use mine either as matching transformers to run
600 ohms to tweeters, or as outputs in a parafeed amplifier with
some low plate impedance tubes and big parafeed caps. It
would probably take about 40-50 uF which isn't too bad.

How are you thinking of using them?

Michael
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Old 26th November 2008, 01:45 AM   #5
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Quote:
Originally posted by Michael Koster
I've decided to use mine ... as outputs in a parafeed amplifier with some low plate impedance tubes and big parafeed caps. It
would probably take about 40-50 uF which isn't too bad.

How are you thinking of using them?

Michael
Bingo!

I am toying with the idea of a monster headphone amp, afterall, these transformers already support multiple secondary taps from 600 down to 1.25 omhs.

-- josť k.
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Old 26th November 2008, 02:45 AM   #6
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Hey Jose, want a monster headphone amp? CCS loaded parafeed.

http://www.tubelab.com/Active%20load...E%20output.htm

The OPT is an LS-33 both 600 ohm windings in series for 2400 ohms. Feed it with a 2A3. CCS load - EL34.

I did do a P-P amp with a single 6AS7 tube as a cathode follower using the LS-33. It was another clip lead monster like the amp in the picture, but I wasn't smart enough to write anything down.
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Old 26th November 2008, 06:20 AM   #7
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Quote:
Originally posted by tubelab.com
Hey Jose, want a monster headphone amp? CCS loaded parafeed.

http://www.tubelab.com/Active%20load...E%20output.htm

The OPT is an LS-33 both 600 ohm windings in series for 2400 ohms. Feed it with a 2A3. CCS load - EL34.

I did do a P-P amp with a single 6AS7 tube as a cathode follower using the LS-33. It was another clip lead monster like the amp in the picture, but I wasn't smart enough to write anything down.

Hi George,

Sure enough, the LS-33 has separate 600 ohm windings from the
voice coil winding. I didn't think about using them in series. Still a
little low on primary inductance but now workable with a range of
tubes. Sounds like you were OK on the low end...

I'm also playing with active load parafeed; nice to see it's been
hashed out in the past.

Thanks!

Michael

PS I figured out how to use the active load to drive along with the
tube, cut the load seen by the tube in half and nearly double the
output power. With this I can avoid wasting the B+ dissipated in
the active load.
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Old 26th November 2008, 07:15 AM   #8
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Look like about 55H primary inductance with the 500 ohm windings
in series. Less than a good parafeed OPT at 2K4 Zpri but more than
a lot of gapped SE OPTs. Certainly enough for a 2A3 or 300B. I just
found the 2K5 parafeed OPT I was seeking for a certain project...

Michael
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Old 26th November 2008, 12:08 PM   #9
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Quote:
Originally posted by tubelab.com
Hey Jose, want a monster headphone amp? CCS loaded parafeed.

http://www.tubelab.com/Active%20load...E%20output.htm

The OPT is an LS-33 both 600 ohm windings in series for 2400 ohms. Feed it with a 2A3. CCS load - EL34.

I did do a P-P amp with a single 6AS7 tube as a cathode follower using the LS-33. It was another clip lead monster like the amp in the picture, but I wasn't smart enough to write anything down.
George,

I know I can always count on you for high-power stuff...

I need a CCS that can handle 200-250ma. Any ideas?

-- josť k.
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Old 28th November 2008, 01:35 AM   #10
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Here are my tube choices for the hybrid tube/sand CCS:

6KG6 - 500mA
GU50 - 230 mA
EL509/519 - 500 mA

Let me know if I've overlooked any.
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