tweed output transformer

[abro163]

Hi, does anyone know what the primary resistance(not impedances) was on the 5e3s OT?

Also if anyone has one; the OT which was shared by bandmaster/super/pro?

Perhaps if anyone has an accurate clone (mercury?) that would be great too.

Thanks

[tubeswell]

Hi Abro, welcome to the forum. FYI I was having this exact discussion under the 5E3 forum. :-)

5E3 OT Load Resistance

8k load resistance is the traditional value. Seems that 6k6 is worthwhile in the pursuit of happiness too.

[abro163]

Thanks for the reply , although that isnt what I am after. I would like to know the resistance of the primary for a 5e3 transformer, (you can just measure with a multimeter). 6k6 - 8k is the impedance.

[tubeswell]

Ah - my apologies. (Have you edited your original post? I see you are also asking about bandmaster etc) Not sure about the resistance on a 5E3 although I imagine it could differ depending on who wound it and how many thousand windings they put into the primary. In any event it will be different on both side of the CT because as the windings are put on the bobbin the layers increase in diameter and you end up with a longer wire on one side of the CT than the other. I did a 5G9 a little while back with a custom made OT that had a 5k primary. That won't be too different from a bandmaster OT (which I think is 4k?) It measured 47 ohms on one side and 60 on the other. I have a 5E3 OT arriving in a day or so. I will measure it and let you know

[tubeswell]

Hi Abro 163

FWIW the pp OT arrived to today for my 5E3 build and it measures 47.9R on either side of the primary CT. But who knows how 'standard' that is?

[abro163]

Thats pretty low resistance, most 15watt are at least 180ohm from plate to plate. I know the old marshall 18watt is 450-650ohm.

The low resistance means either there are low amount of turns or (more likely) that high current / thick wire is used

[tubeswell]

I'd say it's more like thick wire. I got an SE and a PP done at the same time. The pic shows them side by side with a 'conventional' 15W SE OT on the left hand side. (I ordeedr an 18-20Wer for the PP Ot and when I took it out of the box I had to ask the winder about their ratings, and he said 'I reckon the PP OT is probably about 35W" and the SE one is about the same!)

I got the PP OT wound for a traditional 5E3 8k load resistance (should have plenty of smooth bass), but I wonder maybe whether I could get away with a pair of EL34s running them off a 4k load resistance(there are a range of secondary taps to fiddle with). I don't think power handling is gonna be a problem!

The PT for this build (not in picture) is even bigger. 325-0-325@180mA, 6.3V@4A (in case i want to build it with on-board twin-style reverb), and 5V@3A to run a variety of tube rectifiers.

I got the SE OT wound for a 6V6 driven stand-alone reverb build, but I think its maybe overkill (whaddaya reckon?).

[tweed5259]

I'd go for Mojo's Heyboer OT, in my opinion they're the best tweed copies, having tried others myself. I think they're more exact than the mercury.
just my .02.