Hey guys, figured I'd ask here as I'm building an 18-watter project from a vintage set of PT and OT from an old Hi-Fi. I've managed to get the specs of the power-transformer but the specs for the output-transformer are unknown. I've googled around but having a hard time figuring out how to get the primary (HV) and secondary (impedance) values as I have no idea what speaker/speakers were used?
It was used with 2x el84 running ultra-linear (won't be using those screen-taps in new project, however). Power supply was 5v heater-tap for 5y3 rectifier, 6.3v tap for 2xel84 and one 12au7. HV was, if I recall, just over 400v. Filtering was rated 4x 20uf at 450v? If that helps.
Once you figure out the turns ratio, just assume that those EL84's were run into an OT with a primary impedance of 8,000 ohms. Using that, see if the number you get for the speaker side (secondary) makes sense. If you are somewhere near, but in between 4, 8 or 16 ohms recompute using 6.6K and 10K as your assumptions. Soon, you'll get an idea of it. First, though, read that article and figure out the turns ratio.
awesome guys! very informative. so variac on primary until secondary reads 1 volt, then take variac reading "x":1 as your turns ratio, and go from there.
Next in my quest is to figure out who the heck might've made these things. Was surprised at how big the OT is considering just a couple of el84's. Probably something to do with the screen-taps, I guess. That's why I sorta didn't wanna assume 8k on the primary but yes, given the layout, seems likely. I've attached a picture with one bell removed from each. These are from 1956-57. PT and OT look identical. There are, seemingly, a useless string of numbers stamped in the bell. Maybe you guys might have a hint as to where to start researching. I don't figure you could tell just by looking at them but............worth a try.
Thanks for the help!
You do not have the required permissions to view the files attached to this post.
The 412648 on the bell is likely telling you that the transformer was made by General Transformer (EIA code 412), in the 48th week of a year ending in 6... 1966 maybe?
