filament transformer vs plate transformer

[contaxchen]

Hi all,
Does anybody know the funadamental difference between filament and plate transformer? Does filament transformer got more regulation than plate transformer, given the same output voltage?
Any expert?

LungHui Chen

 

[SY]

A filament transformer will be wound to give a voltage appropriate for filaments (or heaters), most commonly 2.5, 6.3, or 12.6V. A plate transformer will generally be wound to give an appropriate voltage for tube plates, typically in the hundreds of volts.

 

[contaxchen]

Ok,
I have some filament transformers with 80v ac... That's quiet high, isn't it? After doubling the voltage, what's the difference between a regular plate transformer?
Lchhen

 

[SY]

At 80vac, they're unlikely to be filament transformers. But with a voltage doubler, there's no reason you couldn't use tham for plate supplies.

There have been tubes made with high-ish filament voltage requirements, but they're nearly all intended for transformerless use (once common in TVs and radios, but abandoned as FAR too dangerous).

 

[ray_moth]

SY already said it. The other important difference is that filament transformer secondary windings have thick wire to supply several amps, wheareas plate transformers are wound with quite thin wire because they need to supply only a fraction of an amp (typically 50 mA - 500 mA).

 

[Shoog]

Will the filament transformer have a poor frequency response.
I am using a filament transformer of 6.3V ac to drive some speaker line transformers in order to get 70V ac. Is the filament transformer likely to be constricting the frequency response of the line transformers ?

Shoog

 

[contaxchen]

Hi,
I know filament transformer got bigger wire and supplies a few amps...
Shoog's question is really meaningful.
Anybody else?

 

[audiousername]

Shoog, the transformer should not have an effect on the frequency response. It is there to provide a voltage. In any case, the transformer is effectively shorted out by the last cap in the power supply (for audio signals).

The drawback of connecting two transformers in series (i.e. stepping the voltage down, then up again) is increased losses - since you are using two transformers. As such it is possible (though not very likely) that the power supply will have such poor regulation that it will sag on demanding passages of music (especially containing bass), but this is the effect of reduced power, not compromised frequency response.

In any case, I don't quite get what you mean by 'constricting the frequency response of line transfomers' - they are being used as power transformers aren't they?

Jason

 

[Shoog]

What I mean by restricting the frequency response is -

Torodial power transformers have a different sound to EI's, so they are effecting the power delivery at certain frequencies. The same question is relivent to filament transformers is it not?

Shoog

 

[audiousername]

Shoog,

The EI type of transformer tends to have a narrower bandwidth than toroids, so more of the HF noise and other rubbish is attenuated. Is that what you mean?

Jason

 

[SY]

With filament (or even HV) transformers, frequency response is quite variable from one construction to the next- it's not a variable that the units are designed for. In fact, the best units have pretty terrible response- you don't want to couple all the HF garbage from the line into your amp. That's one reason that some designers eschew the use of toroids for power transformers.

In any case, there's no general answer- you have to check it on a case by case basis.