Fisher X 100-3 Output Transformer

revisit of an old hack we did, this time with more stuff,

this is an output transformer for a pair of 7189 tubes, but also works well with 6BQ5 tubes,

1960's integrated amp from the Fisher 100 series which had many variations, X-100-A,B,C, 3, X 101, on and on.

there were many different outputs used also, this one sounds real good in a guitar amp driving Amperex 6BQ5's

here is the chassis

Service Manual

shows the p/n for this iron,  T1109-114

here are some open secondary sq wave shots of the secondary

this transformer exhibits many different wave forms as we move up to 1 M Hz sine wave induced generation

Primary Inductance  vs Frequency

this is done with a signal generator,  so we are usung a lower voltage than might be encountered with the transformer in circuit cranking away,

but we should be on the linear side of the B-H curve (not low in the initial perm zone and not too high as to be in the saturated zone, so we can expect these values to hold with an increase in voltage,

here is a graph showing Henries vs Frequency only concentrating on higher frequencies,

pretty good performance, partly due to using .014" grain oriented silicon rather than .019" no grain which will have less perm and more eddy currents due to the increased thickness,

let's  see what happens to the inductance (perm) at 20 Hz as we get off the initial perm floor, (low primary voltage)

let's raise the input voltage level at 20 Hz and see what happens,

looks pretty linear after about 5 volts,

slope of tangent line to curve would be permeabillity.

now let's jack that core up with the Variac at 60 Hz ans see where the smoke comes out,

looks pretty good, not saturation even at 130 VAC,

you would see a slight drop in inductance when we get into saturation.

here is the unloaded upper frequency response curve

print>

Really interesting thread ..  Fisher, 6BQ5 finals, excellent output transformers and sensible circuits.

Whats not to love ? 

I personally like really hefty output traffos for 6BQ5 hifi ...  love some of these Fisher X100-3  real deals!

I have only some poor imitations in the form of 60s Japan versions, which are not bad by any means, but just a bit too 'unmassive' for me, compared to the greats.

My 'local units' Trimax here in Aust are closer in mass to the  American types, just right for the bigger 7591a octal (19W max - beam power type - not 'true pentode' like 6BQ5 et al].

they do have a weird cathode bias scheme that uses tube heaters,

some folks are not too fond of this circuit,

this transformer is a bit smaller than a lot of other 100 series amps , which might be why it sounds so good in a guitar amp,

look at the kilogauss spec on the top left of the first print and you will see what i mean

found a small gaff in the winding print, forgot to erase a "rev wind" text, fixed it

here ya go>

And mee too here [corrected] - I was thinking of the larger op traffos from the Fisher line. of historical note.  It seems these are a little not as large as I was picturing.  ... 

My own japan 60s opt [usual mass]  are then *more like*  these X 100-3, being somewhat  less heaviosity than some of the other great Fisher  classics. 

In my  example, the Japan made and Australia distributed [Melbourne city]    'Encel 6BQ5 Stereo'    ....   

- it does include the whacky [but perfectly calculated] finals'    cathode-current  -  to  heater supply current -  for  the 'low noise' preamp sections  [phono, xtal etc ]

I knew I liked them [and still do] especially as an    'e-gtr with small hi-fi stereo tube amp and pair of 2-way hi-fi speakers'    kind of guy.

Still, the bigger  ..  'slightly beyond 6BQ5'  output transformers of the greats like Fisher  ...  rivet my interest to this day. Dang the cost!

here are the sq wave shots for the original and the rewind, this is before varnish on the rewind,

also, the 0.006" wire that we used, 35 AWG, ohmed out at a higher DCR, so the original wire was probably 34 AWG, but finding #34 with a 0.006" dia could be difficult, maybe a single build from some old Essex might fit, but otherwise the 2600 turns might make the coil to big. such is life when using new wire to replace old wire.

Thanks for all the 'magnetica  CJ'  - they look mostly similar ? maybe less ringing on the rewind ?

bought a Fisher 600 opt, 250 smackers, going to use it for a vox ac 15,

thought to piggyback it onto the other fisher opt i hacked,

not gonna hack this one, but did some measurements, looks like the same coil structure with the bi-fi sec wind in the middle, has a bigger core at 1.5 inches, fisher x-100 is about 1 1/8 inches,

sq wave shots look a bit different, can't wait to hear it!

fisher x-100 on left, fisher 600 on right, unloaded sec sq waveforms