What to do with a 70.7 VRms:4 Ohm transformer

[Demonkleaner]

Circlotron.....

 

[Francois G]

Circlotron.....

Ahah,

 

[Francois G]

In the early wild and wooley days of hifi, some free-thinking folks would try to make amplifiers without any output transformer. (There was even a commercially made one, called a Futterman). These had lots of problems for obvious reasons, but would have been improved greatly with a low impedance, low ratio matching transformer like your pair. The original idea was a little shakey, but might give you some ideas down the road.


All good fortune,
Chris

Haha, funny about the “wild and wooley days”. When did we get beyond that?

However, I had hoped for some definitive suggestions for these trannies as “helper transformers” for OTLs, like the Futtermans.

 

[Ketje]

With 50W and 70V means 100Vtop and 1Atop.
The rus tube 6C33C needs 60V to be able to draw 1A, the two triode parallel.
A circlotron with 2x 160V (½A each) supply and two tubes can drive the transformer up to 50W.
The heater alone need 80W already, ot very economical.And 2x 100Vtop to drive the grids.
But, it could be done.
Mona

 

[Chris Hornbeck]

With 50W and 70V means 100Vtop and 1Atop.

So, if we're confident that design center is for 50 Watts (this really should be measured first, for a turns ratio of square root 100/4 = 5) then an 8 Ohm nominal speaker load will give the valves a 200 Ohm nominal load. As you say, can be done, but seems almost a solution in search of a problem. But, hey, that's hifi.



All good fortune,
Chris

 

[PRR]

So, if we're confident that design center is for 50 Watts ... then an 8 Ohm nominal speaker load will give the valves a 200 Ohm nominal load....

I thought the link had been posted, but apparently not.
http://greatplainsaudio.com/wp-content/uploads/2016/06/9441A-01.pdf
15170 is the accessory to the 9441A 2x100W@4r amplifier to give transformed outputs. While not on this sheet, Francois reports they say 70.7V on them.

So the nominal spec is 20V:70.7V (1:3.5) or 4r:50r 100W. Or off-spec, 8r:100r at 50 Watts.

Yes, it could work as a transformer for a transformerless tube amp. (Does that even make sense?) Futtermans etc can do well at 50-100 Ohms without a boat-load of bottles.

Yes, they are nice cores and you can find out how many turns Altec thought best for a 4r winding, figure other windings from there.

 

[U130421]

I doubt distributed speaker system requires high quality transformer, as the receivers use low quality autotransformer . Measure first the frequency response by injecting in 70v and load the 4 ohm . If it is a quality sectorized winding then if you open the covers you may find the 70v center tap . You can then use a low impedance output as push-pull cathode follower.
It is not because it hasn't air gap that few milliamps dc it will saturate . You can try out with an emitter follower with 4 & 8 ohms load and see up to how much watt it sounds good bass . To my experience, as I always use power supply transformers while dimensioning a tube circuit , you should get 1/4th of the power in single ended , that is 12w is possible.

 

[Francois G]

Thank you all, gentlemen, for the good input. The Greatplainsaudio link is especially useful, thank you PRR. Your discussions will be a valuable guide when I start experimenting with these transformers.

On the other hand, the cores look excellent, perhaps I will use them for my first attempt to wind my own coils.

Thanks again!

 

[odilon_df]

Thanks for your assessment. It has a single coil on both primary and secondary side, like most distribution transformers I have heard of (no experience with them - that why I’m asking the experts). I don’t know if it is gapped or not. So, does that mean I can’t use this transformer for tube anything? Maybe transistor output? Or how about the Phillips EL86 cascade output stage meant for their OTL 800 ohm speakers (while driving 8ohm speakers)?

Has you think about use as an output with 8 triode sections (4 x 6as7) Output impdance is only 250ohms per secion , divide per 8).... almost an OTL ... i guess you gan get 40w p/channel and a good impedance ? google for audiomirror...
or DIY Loudspeaker Projects Troels Gravesen › AudioMirror a lot of information....