Looking to trade transformers. / Sale and Trade / Forums

Forums

4hv.org :: Forums :: Sale and Trade

« Previous topic | Next topic »

Looking to trade transformers.

Move Thread

LAN_403

steve516

Sat Jul 16 2011, 08:20PM

Registered Member #3832 Joined: Thu Apr 14 2011, 11:57PM
Location: Downtown Chicago, IL
Posts: 37

So it looks like I need a higher voltage than I originally thought for my transmitter.

I'm seeking a 1800VCT (900-0-900) plate tranny at AT LEAST 120ma. and a 120v primary. doesn't need filament windings.

In exchange, I have a large 1160VCT @ 160ma, with a 150V winding, dual primary with 120/240 support, and several filament windings. It has at least 10 amps at 6.3v, and I believe it's also 10 amps with a couple 5v windings.

PM and we'll chat.

Steve

steve516

Mon Jul 18 2011, 01:05AM

Registered Member #3832 Joined: Thu Apr 14 2011, 11:57PM
Location: Downtown Chicago, IL
Posts: 37

I would be interested in simply buying one as well...

Patrick

Mon Jul 18 2011, 01:45AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

1800V CT, at least 120 mA, 120 primary? sounds like a MOT? right?

Arcstarter

Mon Jul 18 2011, 02:01AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

I would be willing to trade a MOT for that transformer indeed

Herr Zapp

Mon Jul 18 2011, 02:19AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Patrick wrote:

"1800V CT, at least 120 mA, 120 primary? sounds like a MOT? right?

Well no, not at all.

1. Construction-wise, MOTs are about the most cheaply-made transformers you'll ever encounter. Commercial plate transformers are built to a much higher standard.

2. Design-wise, most MOTs are on the edge of core saturation at nominal line voltage, and are designed for low duty cycle, intermittant use. Commercial plate transformers are made for continuous operation at high ambient temperature, and generally have a large reserve capability to handle intermittant overload without damage. Plate transformers will delivery their rated secondary current 24/7.

3. MOT HV secondaries are never center-tapped, while plate transformers almost always have a center tapped secondary. It's also very common for plate transformers to have multiple secondaries to allow 120 or 240 VAC input, and multiple secondary taps to provide multiple choices for the output voltage.

Because of these factors, MOTs are essentially free, while good quality used plate transformers from the classic American manufacturers still command high prices, regardless of age.

Herr Zapp

steve516

Tue Jul 19 2011, 12:04AM

Registered Member #3832 Joined: Thu Apr 14 2011, 11:57PM
Location: Downtown Chicago, IL
Posts: 37

Herr Zapp wrote ...

Patrick wrote:

"1800V CT, at least 120 mA, 120 primary? sounds like a MOT? right?

Well no, not at all.

1. Construction-wise, MOTs are about the most cheaply-made transformers you'll ever encounter. Commercial plate transformers are built to a much higher standard.

2. Design-wise, most MOTs are on the edge of core saturation at nominal line voltage, and are designed for low duty cycle, intermittant use. Commercial plate transformers are made for continuous operation at high ambient temperature, and generally have a large reserve capability to handle intermittant overload without damage. Plate transformers will delivery their rated secondary current 24/7.

3. MOT HV secondaries are never center-tapped, while plate transformers almost always have a center tapped secondary. It's also very common for plate transformers to have multiple secondaries to allow 120 or 240 VAC input, and multiple secondary taps to provide multiple choices for the output voltage.

Because of these factors, MOTs are essentially free, while good quality used plate transformers from the classic American manufacturers still command high prices, regardless of age.

Herr Zapp

You are correct. A MOT would not work in these circumstances. I've got a pair of identical 2200V MOTs I'm saving to create a CT transformer for an 813 rig I plan to build.

Right now the old transformer is putting out about 750V after 866a FW rectification and filtering. Seeing as I need 1100V for this 807 series mod rig and that this was my first experience with FW rectification as opposed to bridge, I was not aware that you only get the peak voltage (so 1.414xRMS) of each side of the CT. Hence how I ended up needed a bigger transformer.

hmm.
Steve
So 860-0-860 is what I'm aiming for right now. I figure someone has to have one...

Sulaiman

Tue Jul 19 2011, 12:18AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

If you use two MOTs each with the magnetic shunt removed;
with primaries in series and secondaries in series
you would get approximately the desired result.

Putting the primaries in series halves the voltage
... well below saturation

Removing the shunts would remove the large output impedance.

The primaries would of course have to be connected so that the secondaries are 180 degrees out of phase.

You can use the existing heater windings in series or parallel.

You could remove the heater windings and wind your own.

Patrick

Tue Jul 19 2011, 04:34AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Herr Zapp wrote ...

3. MOT HV secondaries are never center-tapped, while plate transformers almost always have a center tapped secondary. It's also very common for plate transformers to have multiple secondaries to allow 120 or 240 VAC input, and multiple secondary taps to provide multiple choices for the output voltage.

Herr Zapp

well every MOT ive seen has two poles out of the HV secondary, with the core being attached to the midpoint of the secondary, thus a defacto CT... but you do what ever you "tube people" want.

Herr Zapp

Tue Jul 19 2011, 05:15AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Patrick wrote:

"well every MOT ive seen has two poles out of the HV secondary, with the core being attached to the midpoint of the secondary, thus a defacto CT..."

Not so, at least not for a conventional magnetron driven oven. Look carefully at any MOT. You'll see that there is only one HV terminal, from one end of the secondary. The other end of the secondary is connected directly to the transformer core.

Or, look at any of the scores of microwave oven schematics on the web; they will clearly show the non-center-tapped secondary. The standard voltage doubler circuit, with one HV capacitor and one HV rectifier, would not work with a center-tapped secondary.

(Don't confuse the two ends of the heavy-gage, heavily-insulated filament winding for the single HV output winding.)

Herr Zapp

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob