• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

What kills an opt tranny?

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#21
poobah said:
You don't really want to change the impedance... at least not without a well thought out reason. The impedance of the OPT should be matched to the tubes (and loads) used in the circuit.

🙂
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You obviously don't play quitars......nearly all guitarists in my circle tamper with the o/p configuration on my tube amp (i.e 8ohm on 4 ohm and 4 ohm on 15 ohm tap) because the variation sounds better on particular strings. It so happens the o/p tranny is generously rated.
The story is different on hi-fi.
A secondary short circuit just slams the output tubes harder.

O/P trannies which are large implies more lower freq extention. Bass guitar o/p trannies usually have cutoff around 40Hz and need not go lower. A hi-fi version going down to 20Hz is roughly double the size and weight. So don't expect much power out of a bass guitar tube o/p tranny used to reproduce the lower end of an organ pedal. But one does come across tube MI amps used for hi-fi applications.
Using parallel push pull is an excellent way of reducing the winding and leakage parasitics because Z is halved. That means less copper and less layers and better HF and phase response and o/p tranny manufacturers like winding'em.

richj
 
#22
Now... all other things being equal (impedance for one); a smaller transformer means less inductance and does mean less bass. So... a larger transformer can mean more bass. This is a very general statement; with lots of exceptions.
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this is because fewer windings can be put in a smaller transformer than a bigger one.😀
 
#23
Tony said:


this is because fewer windings can be put in a smaller transformer than a bigger one.😀
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No..... Youv'e forgotton the number of turns which implies inductance plus smaller gauge wire can be used whereas a larger core can have less turns for same inductance than a smalller one has..
The Ae (cross sectional area) is important for assessing how much throughput power the core can handle before saturating. A smaller core obviously less.

So the 40Hz cutoff output tranny has a smaller core simply because it has a lower inductance and the core cannot handle lower frequencies at the same power before magnetically saturating.

In practice a core which has fewer turns for the same inductance must be more reliable than a smaller one with many more turns.

Magnetics needn't be a magic art!
richj
 
#26
RDH4 had a comprehensive section on this... that would be a good place to start.

It is not impossible, but it ain't easy...

The "art" comes into the picture because everything must be comprimised, many of the governing equations are nonlinear, and materials have finite limits. Don't expect to get 20Hz - 200kHz on your first try.

Go for it though... you'll learn a ton.

🙂
 
#27
richwalters said:


No..... Youv'e forgotton the number of turns which implies inductance plus smaller gauge wire can be used whereas a larger core can have less turns for same inductance than a smalller one has..
The Ae (cross sectional area) is important for assessing how much throughput power the core can handle before saturating. A smaller core obviously less.

So the 40Hz cutoff output tranny has a smaller core simply because it has a lower inductance and the core cannot handle lower frequencies at the same power before magnetically saturating.

In practice a core which has fewer turns for the same inductance must be more reliable than a smaller one with many more turns.

Magnetics needn't be a magic art!
richj
Click to expand...

yes, this is exactly what i meant, guess i'm a sucker for one liners, sorry..


😀 😀
 
#29
4) I have seen people connect zener strings and even VR tubes across the OPT primary.
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Simple rectifier diodes to ground work. When flyback causes the primary to go below ground it's clipped by the diode. Two or three *4007 in series is plenty. Those and a 200 ohm resistor across the secondary will save most amps if the speaker becomes disconnected.

I saved from a dumpster a box of 15 ohm 50W power resistors. I have installed them in guitar amps so that they get connected when the speaker is unplugged.

-- Dave
 
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