Tweed 5E7 bandmaster primary Z, please check my math ;)

[azatplayer]

Just trying to work out what OT values i need for a build.
Been listening to some bandmaster tone, and its all good. Im not gonna go down the path of 3 x 10, sadly, not yet anyways, as im stuck on the portability of a 1x12.
Therefor the primary Z is what im trying to figure out, math not being my strong suit..
The bandmaster had a 6K primary and 4ohm output, but saw a 2.7ohm load from the 3 x 10's.
I get a turns ratio of 1 to 1500 from the 4ohm to 6K, so multiplying the ratio by 2.7 gives me 4050 primary Z.
i have 3 OT's on hand, a 4, 5.2 and 6.6. Just wanna nail the amps character, circuit wise, as alltho its the same circuit as the bassman and super and pro apart from rectifiers and fb values, its the impedance adding to its character.
Can someone please check my math?

[tubeswell]

The bandmaster had a 6K primary and 4ohm output, but saw a 2.7ohm load from the 3 x 10's.

Yup assuming an impedance ratio of 1500:1 and a load of 2.7R on the secondary, 2.7R x 1500 = 4050R

[Blind Lemon]

Most Fender 2 6L6 amps run @ about 4.2K, but what is also important in the character of these amps is the size and wattage rating of the transformer. For a Tweed amp like the BandMaster I'd be looking for a smaller rather than larger OPT. When these old Tweed amps are driven I believe OPT saturation is part of their tone. Yes Leo was going mostly for clean tone, but thankfully he didn't achieve that in some of his early amps.

Just may 2 cents.

BL

[marcoloco961]

Just trying to work out what OT values i need for a build.
Been listening to some bandmaster tone, and its all good. Im not gonna go down the path of 3 x 10, sadly, not yet anyways, as im stuck on the portability of a 1x12.
Therefor the primary Z is what im trying to figure out, math not being my strong suit..
The bandmaster had a 6K primary and 4ohm output, but saw a 2.7ohm load from the 3 x 10's.
I get a turns ratio of 1 to 1500 from the 4ohm to 6K, so multiplying the ratio by 2.7 gives me 4050 primary Z.
i have 3 OT's on hand, a 4, 5.2 and 6.6. Just wanna nail the amps character, circuit wise, as alltho its the same circuit as the bassman and super and pro apart from rectifiers and fb values, its the impedance adding to its character.
Can someone please check my math?

What is the ohm rating of the single 12" speaker you are going to use?
From what I see of your data, the original primary would have been 4050 as you stated. So the 4K OT you have should be closest to original spec. as long as you have the proper speaker load to the proper secondary winding.

[azatplayer]

Yes good point about the size, thats pretty important for sure, tho ive also read that a lot of them shat themselves and had OT replacements done.
I might get Heyboer to wind me something yet.
I will be using either a single speaker or a pair, so will have need ofthe three output taps.
I was reading a post by Bruce at mission amps, regards the early stuff, he states the OT's used were 6Kish, before changing to 4Kish later on, he also says its pretty subtle stuff, but the primary change with those 3 speakers is part of that particular amps magic, oddly enough reflecting the 4K of the later models, tho not as clean. Great sounding tweed. Ive done a couple of 5E3's and theyre a solid little amp, but i just have a need for those bigger bottles running less efficiently, about 28 watts could be perfect!

[greenbottle]

If you look closely, at enough Fender ccts, you start to see the simularity in different models in the same era. eg look at the Bandmaster,the Pro and the Super. As an other example look at Circuit AB763 ( Black Face era), You will find it in models rangeing from Delux Reverbs all the way up to Twins. Some will only have treble and bass controls in one channel. some will have 6V6 outputs, some will have 2 x 6l6 outputs some will have 4 x 6l6 in the output.

The only reason that Leo put 3 speakers in bandmasters was possibly to have an amp at a particular price break that came in between
two other Fender amps and to heck with the impeadence mismatch. All of the large amp manufacturers are very COST conscious. They endeavor to produce an acceptable amp at the lowest cost. One dollar a unit doesn't sound much but over 10,000 units it becomes signifignant. How many Fender Twins are there in the world?

So the world is your oyster. You can have 1 or 2 or 4 speakers. Find a Fender cct of the appropiate era with the same output configuration and choose the appropiate OT. I bet you will find that Mojo will have your OT in 4,8,16 ohm.

Alan