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4hv.org :: Forums :: General Science and Electronics
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building a modulation transformer with a mot?

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803
Wed May 12 2010, 04:14PM Print
803 Registered Member #2807 Joined: Fri Apr 16 2010, 08:10PM
Location:
Posts: 191
 		Hi has anyone tried to build a mod. transformer? Could you build one with a mot? A mod. tras. is just a current mod, right? Anyone try using a magnetic amplifier as one?

Thanks,

Paul
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radiotech
Wed May 12 2010, 05:32PM
radiotech Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
 		Can you be more specific: What is the transformer modulating and what is driving it and what frequency response will the modulation have?

Magnetic amplifiers are modulators; Some modulate /50/60 Hz
(carrier) with a frequency response from DC to a few Hz.

This is a mag amp transformer that I grabbed when a old battery charging system was upgraded to solid state controls. Notice the big outer coil- (AC load winding) and the two differentially connected
DC control windings. Two cores are used
1273685573 2463 FT89046 Bampxfm
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803
Wed May 12 2010, 05:49PM
803 Registered Member #2807 Joined: Fri Apr 16 2010, 08:10PM
Location:
Posts: 191
 		the transformer is modulating a 1100 watt vttc. It's driving nothng, just liminting the current based on the audio unput to the mag amps cuntrol input. freq, few kiloherz-50 khz
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Arcstarter
Wed May 12 2010, 06:37PM
Arcstarter Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
 		Why not buy an audio transformer? They are readily available and have a fairly large bandwidth.
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803
Wed May 12 2010, 07:06PM
803 Registered Member #2807 Joined: Fri Apr 16 2010, 08:10PM
Location:
Posts: 191
 		don't they cost a buldle? anywho, how you cheacked to tag to a 550 watt tras? Over a 1000! ( from stores)
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Proud Mary
Wed May 12 2010, 07:27PM
Proud Mary Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
 		If this is for use with your 803 pentode, you could use screen grid modulation which requires less power and is more economical with parts than anode modulation.
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803
Wed May 12 2010, 07:35PM
803 Registered Member #2807 Joined: Fri Apr 16 2010, 08:10PM
Location:
Posts: 191
 		thank you

but do you have a example of screen modulation that I could use?

PS why does one of the members always call you Harry?
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radiotech
Wed May 12 2010, 07:59PM
radiotech Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
 		Screen modulation cannot fully modulate the carrier.

To try a MOT connect the filament winding to the output of 100 watt or so audio amp. Connect the HV secondary in series with the bottom end , (DC feed) of the TC) Connect a 1000 uufd/3000 volt cap across the HV secondary too.

screen modulation using a tube : >


1273694370 2463 FT89046 Scan0004
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803
Wed May 12 2010, 08:02PM
803 Registered Member #2807 Joined: Fri Apr 16 2010, 08:10PM
Location:
Posts: 191
 		but why only 100 watts? don't you need 1/2 the wattage input for 100% mod? how would the number of turns on the mot affect mod?
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Proud Mary
Wed May 12 2010, 08:12PM
Proud Mary Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
803 wrote ...

but do you have a example of screen modulation that I could use?

just Google "screen grid modulation"



803 wrote ...

PS why does one of the members always call you Harry?

That's funny, I was just about to ask you why people kept on calling you Susan.
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