Drake 784-139 history?

AndyD

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Could someone please enlighten me as to its history? How long was this transformer produced and how did it change over the years? Were earlier ones "better"?
 

TAZIN

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I'm unaware of any major revisions to the 784-139; therefore, the early units should be electrically equivalent to the later ones.
 

AndyD

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According to someone I used to correspond with at Drake 20 years ago the 784-139 was released June of 1967. It was sectionally round alternating between secondary and primary.

I'm unaware of any major revisions to the 784-139; therefore, the early units should be electrically equivalent to the later ones.
That's very helpful, thank you. So when did Drake stop making the -139?
 

TAZIN

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That's very helpful, thank you. So when did Drake stop making the -139?
I would guess that the 784-139 was used into the 1980s for some of the JCM800 stuff. By 1993 the 784-139 was used again in the 1987X reissue. I assume they are Drake units and not manufactured by another company just using the same reference number...
 

StingRay85

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Do you know the difference between Drake 784-139 and 784-213? It was used in Carlsbro 50W EL34 amps, but to me it seems a different reference code for the same OT.
 

AndyD

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Do you know the difference between Drake 784-139 and 784-213? It was used in Carlsbro 50W EL34 amps, but to me it seems a different reference code for the same OT.
I would love to know the answer to this as well !!! @neikeel any thoughts?
 

TAZIN

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Do you know the difference between Drake 784-139 and 784-213? It was used in Carlsbro 50W EL34 amps, but to me it seems a different reference code for the same OT.
I remember reading somewhere that the 784-213 has a slightly high primary impedance...
 

neikeel

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AFAIK the -139 is 3.4k primary and the -213 is more like 4k. I've had a couple but not measured them , n fact just remembered - I may have one in a 50w PA in a cupboard so can scope it/measure when I get chance.
 

StingRay85

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I had to figure out the color of the leads, but this should be correct:

Primary is black & yellow with red center tap
Secondary is black center tap brown 4 ohm yellow 8 ohm green 16 ohm

According to my voltage measurements, resulting in primary impedance of 3.83K (16 ohm) 4.07K (8 ohm) and 4.15K (4 ohms). On the schematic they are given as 15, 7.5 and 3.75 taps.

So I guess indeed a bit higher than 784-139
 

Ned B

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I recall that Dave from Drake said that there was a difference with the sectional order between the Marshall models and off the shelf. like P/S/P/S/P/S/P or S/P/S/P/S/P/S. I can't remember which was which.
 

StingRay85

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Since the 213 has 3 primary leads, and 4 secondary, it would make sense to have S-P-S-P-S-P-S
 

AndyD

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I had to figure out the color of the leads, but this should be correct:

Primary is black & yellow with red center tap
Secondary is black center tap brown 4 ohm yellow 8 ohm green 16 ohm

According to my voltage measurements, resulting in primary impedance of 3.83K (16 ohm) 4.07K (8 ohm) and 4.15K (4 ohms). On the schematic they are given as 15, 7.5 and 3.75 taps.

So I guess indeed a bit higher than 784-139
So presumably one could run the -213 on the 16ohm tap (3.83K) with a 8 ohm speaker load to get it closer to the 3.4K impedance of the -139?
 

StingRay85

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In that case it would be a lot further off. There difference between 4K and 3.4K seems marginal.
 


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