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