Toroid Power Transformer as Output Transformer ???

[Kagliostro]

Hi all

In an Italian forum I've read that is possible to use a Toroidal Power Transformer as Output Transformer

the author of the article experimented it for HiFi use (not guitar)

he build a SE 3W (EL34) amp using a 220v/12v 100W transformer

he specified is important to have a big transformer as to reach good low frequency response

here the site

http://www.audiocostruzioni.com/

on the left of the screen look to:

AUTOCOSTRUZIONE DIY

than

Elettroniche

there look for "Valvolozzo"

or look to the site of the author

http://www.diegobarone.it/Valvolozzo.htm


He say that results were very good

Have you experimented something like that for guitar amp use ?

in guitar amp use do you think that the transformer must be "oversized" at a high level or it will be possible to use a 100/150w transformer for a 50/60w amp ?

I've a pair of EL504 that woud like to have a load around 2.600ohm ..........

and a 115v-115v/12v 100W transformer with an 8ohm speaker seems to be good for that use (on the paper is a 2.939Ohm primary with 8ohm load)

Curious to read your opinions and/or experiences

Kagliostro

[soma_hero]

https://tubeamparchive.com/viewtopic.php?t=7148

[Kagliostro]

Thanks for the link

Sometime ago a friend experimented with Power Transformers

not Toroidal

as Output Transformers but results wasn't encouraging

(he had also some measurements with oscilloscope and signal generator)

Kagliostro

[David Root]

I don't see the point. Power transformers are not designed to be used as output transformers. Toroidal OTs are available and would work better.

[Kagliostro]

I don't see the point

New Toroidal Power Transformers has price very very lower than official Output Toroidal Transformers

Used Toroidal Power Transformers can be find at really VERY low price at flea markets

Kagliostro

[ToneMerc]

I don't see the point

New Toroidal Power Transformers has price very very lower than official Output Toroidal Transformers

Used Toroidal Power Transformers can be find at really VERY low price at flea markets

Kagliostro

In general the appropriate OT transformer can be found, so 99% of us have no need to ever want to attempt this. Therefore, you shouldn't be surprised if the majority of the replies on this forum are, "what's the point", of which I concur.

I certainly don't have a problem wanting to saving money. However, at the same time, I won't jump over a dollar just to pick up 15 cents either.

Sometimes only a rich man can afford to buy flea market cheap.

TM

[Structo]

For whatever reason, the toroid transformers seem to be used mostly by our European brothers.

I'll have to confess to never trying one or knowing much about them.

I see it as a neat technology but the larger footprint can cause some problems.
I like how it is not very tall so in many cases it could fit inside a chassis.

[rdjones]

Thanks for the link

Sometime ago a friend experimented with Power Transformers

not Toroidal

as Output Transformers but results wasn't encouraging

(he had also some measurements with oscilloscope and signal generator)

Kagliostro

Many moons ago I tried the same thing. (not toroidal)

Large TV power transformer with the center tapped HV as the primary and
various combinations of the 5V and 6.3V filament windings (alone or in series) for the secondary.
It "worked". I assumed that the large eddy strap effected the response and efficiency.
The amp was originally UL, though, and I eventually found a proper OT from a similar unit (Bell Pacemaker PM75)

I still have said power tranny waiting to be used in another project if needed.

rd

[Merlinb]

The trouble with using power transformers as output transformers are manyfold. There are the obvious issues of poor linearity and HF response, but for guitar use the following are the main concerns:

Firstly, there is a lack of primary inductance. The keep the primary impedance at the desired level down to low freq's, you need plenty of primary inductance, usually 20 to 100 Henrys. An EI transformer may have a primary inductance of a few Henrys, and a toroidal may barely reach one Henry! Major bandwidth limitation...


The second is saturation. A PT is designed for mains frequency and voltage. If you apply a lower frequency, or a higher AC voltage (or both!), then the transformer will saturate and get hot, as well as distort with plenty of odd harmonics. In a guitar amp you might get away with frequency, since you are unlikely to be amplifying anything below 50Hz, but typically you will have AC voltages well in excess of 230Vac, which will cause saturation.

I have used PTs in very small (sub 1W) amplifiers, but the lack of primary inductance always makes them sound a bit weedy to my ears. To really get it to work you would need an application that required a fairly low-impedance primary, and low AC voltage swings. To me that implies a sub-250V, class AB, high current triode amp.

[Cliff Schecht]

To really get it to work you would need an application that required a fairly low-impedance primary, and low AC voltage swings. To me that implies a sub-250V, class AB, high current triode amp.

Or a solid state output section .

[Kagliostro]

MANY THANKS TO ALL

Kagliostro