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Author Topic: Eico 730 Modulator  (Read 2196 times)
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k5ygc
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« on: January 20, 2022, 02:07:55 PM »
Thinking of having Heyboer build a modulation transformer to match up with Eico 720. 5k primary with feedback tap and center tap.  10k secondary is this correct? Mark K5YGC
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DMOD
AC0OB - A Place where Thermionic Emitters Rule!
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« Reply #1 on: January 20, 2022, 10:20:31 PM »
Quote from: k5ygc on January 20, 2022, 02:07:55 PM
Thinking of having Heyboer build a modulation transformer to match up with Eico 720. 5k primary with feedback tap and center tap.  10k secondary is this correct? Mark K5YGC

Page 1 of the Eico 730 Modulator Driver Manual says:

Output Transformer Matching Impedance: 500 ohm and 10,000 ohms.

https://bama.edebris.com/manuals/eico/

Phil - AC0OB
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k5ygc
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« Reply #2 on: January 21, 2022, 11:04:35 AM »
Secondary connection is pin 4 which is 5k to the Eico 720. So what is the primary impedance?
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DMOD
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« Reply #3 on: January 21, 2022, 03:27:27 PM »
Quote from: k5ygc on January 21, 2022, 11:04:35 AM
Secondary connection is pin 4 which is 5k to the Eico 720. So what is the primary impedance?

Plate-to-Plate primary load impedance is 6.5k for the Vp operating voltage of the 730.

For an Impedance ratio of 1.3 (6.5k/5k), the turns ratio from Primary to Secondary is 1.14:1.

I would have thought that Hayboer would have this information.

Phil
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DMOD
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« Reply #4 on: January 21, 2022, 04:55:54 PM »
Quote from: k5ygc on January 21, 2022, 11:04:35 AM
Secondary connection is pin 4 which is 5k to the Eico 720. So what is the primary impedance?

Are you sure of the 5k figure?

I just calculated a load impedance of 2550 ohms for the 720's 6146's final and that is the impedance the 730 will be working into.

It appears the 2.5k impedance winding would be the better secondary winding.

Correction:

This would result in a turns ratio of ~ 1.2:1, for an impedance ratio of 1.4:1, primary to secondary.
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Charlie Eppes: Dad would be so happy if we married a doctor.
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k5ygc
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« Reply #5 on: January 22, 2022, 07:13:11 AM »
Quote from: DMOD on January 21, 2022, 04:55:54 PM
Quote from: k5ygc on January 21, 2022, 11:04:35 AM
Secondary connection is pin 4 which is 5k to the Eico 720. So what is the primary impedance?

Are you sure of the 5k figure?

I just calculated a load impedance of 2550 ohms for the 720's 6146's final and that is the impedance the 730 will be working into.

It appears the 2.5k impedance winding would be the better secondary winding.

This would result in a turns ratio of 1.6:1, for an impedance ratio of 2.6:1.
Pin 4 is going to the 6AQ5 and then to the grid of the 6146.
I wished they had the info life would be easier.
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