Recovered Transformer from 80W SS amp 40v-0-40v - available current ?

[kagliostro]

I recovered a 40v-0-40v Power Transformer from a dismanted SS 80W amp

the label on the amp says 235W consumption

Is correct if I assume an efficiency of near 80% and an available current of 2.3A at 80v or 4.6A at 40v ?

Thanks

K

[eleventeen]

Sounds reasonable.


Let me issue you one caution: Very often, such transformers for SS gear will have TWO secondaries, or at least they LOOK like they have 2 secondaries. For example, 40-0-40 and 15-0-15. That would not do you much good in the tube world. I have several such transformers obviously from SS gear with a 80 volt secondary and a 160 volt secondary. Although powering heaters will always be a problem (need a separate heater transformer) the mental wheels start turning and I start thinking "Hmm, if I placed those secondaries in series and ran a voltage doubler I should be able to get 425-450 volts."


In every case, however, the secondaries are "nested". In other words, they look like this:





And so the secondaries cannot be placed in series. (without sparks and smoke)
 

[kagliostro]

Thanks Eleventeen

This particular transformer has only a 0-220v-240v primary and a 40v-0-40v secondary

I was thinking to something like 80v AC (CT disconnected) and a quadrupler

to obtain near 450v @ ~500mA (of which I think to use only 1/2)

as you say the problem is I must use a separated heater transformer

Franco

[jjasilli]

You've got tons of amperage on the secondary side.  With a voltage quadrupler, you'd net say 300V or so, and still have 1/4 the amperage, or over 1A available.  That could power, say, a quad or more of power tubes.  As you go from voltage doubling to tripling, quadrupling, etc., noise & hum go up.  But what the heck depending on the application. 

[PRR]

> dismanted SS 80W amp
> the label on the amp says 235W consumption

80W total? Or 80 watts per side, twice for stereo?

80+80= 160W total output. 235W input and 160W sine-wave audio rating is fairly close to right.

Since the PT is clearly all or most of the 235W input, you can work out the rating.

> 40v-0-40v

So 80 Volts AC total. 235W = 235 VA. 235VA/80V= 2.9 Amperes AC.

Efficiency may be better than 80%, but I will agree with your 2.3 Amp AC rating.

Now try some sanity checks.

The 80V into a rectifier capacitor DC supply will give about 113V DC (40-0-40V implies +/-56VDC). A perfect amplifier, fed 113V, can give up to 40V Sine RMS output. In 8 Ohms this is *200* Watts sine output.

Are you sure of the "40v-0-40v"?

Was the amp maybe wired with the 2-rectifier plan, to give a single 56V supply? This would give 49W in 8 Ohms, which might be 80W in 4 Ohms. That does make sense.

As a Quadrupler, it may not quite make 450V 500mA; but that would be a BIG tube amp (over 100W) and you can make plenty of sound even if it comes out a little shy of 450V.

[kagliostro]

Thanks PRR

The amp was the Roland DAC 80D 80W guitar amp I recovered, so, no stereo

The transformer has a primary with 0-220v-240v and the secondary is only 40v-0-40v

if it is useful I can weigh and measure

Attached, in the .pdf file, the spech of the amp (EDIT: the speaker is an 8ohm)

Franco