wires of output transformer are too thin!

[zxx123]

hi,
I bought a pair of used output transformers.

I've found that wires of primary stage are so thin
as pig hair, however, secondary ones are thick.

Is this size normal? Does it affect quality of sound?

[Bill Fitzpatrick]

Primary wires are thin in order to get windings on the order of 5K ohms. The current through them is small so the the wire gauge can be small. Not to worry.

[AndyN]

http://www.alphawire.com/pages/383.cfm

According to a quick Googling of AWG tables, hair-fine 30 Gauge will carry ~2 Amperes. Derate that by 50% for bundled wires - so say 1 Amp. The plate current of a really cookin' 300B amp is 75 mA = 0.075A. So that's quite a safety margin.

As for the difference in gauge between primary and secondary:

Without going to the bookshelf, the voltage and current are doing inverse things across the windings. An output transformer is a step-down device - say 5000:8, . But in this context, "step down" is referring to voltage, not current. Current does the inverse - it's magnified, so to speak.

So small fluctuations in that 0.075A current is going to be turned into large current fluctuations in the secondary. Cone speakers, being horribly ineffecient devices (on the order of less than 5% ?) need that current to move.

All in all, it sounds as though you have a properly designed transformer.

[Sch3mat1c]

Originally posted by AndyN
http://www.alphawire.com/pages/383.cfm

According to a quick Googling of AWG tables, hair-fine 30 Gauge will carry ~2 Amperes.

Uhhhhhhhhhhhhhhhhhh.........





Holy cr@p!

Derate that by 50% for bundled wires - so say 1 Amp.

Like using your OPTs as expensive fuses, eh?

Come on... even not-so- common sense tells you no ordinary OPT will handle half that without melting. 1 or 2A will melt the copper wire itself, fusing it (literally, using the 30ga wire as a fuse).

Tim

[contaxchen]

Holy cr@p!

How about 2cm wide of coper foil on PC board can carry 1A current? This is what I read from a standard textbook.
Lhchen

[Layberinthius]

Originally posted by AndyN
http://www.alphawire.com/pages/383.cfm

According to a quick Googling of AWG tables, hair-fine 30 Gauge will carry ~2 Amperes. Derate that by 50% for bundled wires - so say 1 Amp. The plate current of a really cookin' 300B amp is 75 mA = 0.075A. So that's quite a safety margin.

As for the difference in gauge between primary and secondary:

Without going to the bookshelf, the voltage and current are doing inverse things across the windings. An output transformer is a step-down device - say 5000:8, . But in this context, "step down" is referring to voltage, not current. Current does the inverse - it's magnified, so to speak.

So small fluctuations in that 0.075A current is going to be turned into large current fluctuations in the secondary. Cone speakers, being horribly ineffecient devices (on the order of less than 5% ?) need that current to move.

All in all, it sounds as though you have a properly designed transformer.

I'm going to stick my head out here and exclaim that the derating factor which is present on that website is determined only for wires which are bundled/insulated for use in interconnecting purposes and not coil winding for use in situations where eddy currents require consideration.

If you take a look at an ordinary wire which you use inside your amplifier (and any other project) you will notice that there is not just one wire connecting point A to point B, if there were, it'd be incredibly hard to solder one to a point (within reason) and to bend the wire around a corner or whatnot, I think this is what that website is mainly used for.

I personally have no knowledge of proper cable ratings for transformers or interconnection wires but what I just said "sounds about right" to me anyway.

If you can get the jist of it =).