Maxed out power tubes then an output volume?

mrjones2004x

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This is probably already a thing with current amp designs so if I’m thinking outside the box and wrong let me know.

why don’t companies make amps that are low wattage so to speak so you can crank them up or even max them so power tubes are in saturation and have a secondary power side which can just raise the total output volume? I guess kinda like going to a pa? But built into say a head or combo as one?

tell me to shut if if this already the case :2c:

So say a 1 watter can sound beautiful at a home level or also be turned up to a gig level with output volume circuit.
 

mrjones2004x

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It already exist. They use ecc83 for that

that’s a preamp tube tho?
All the fizz no warmth and thickness till the power tubes start to saturate.

my 2501 sounds terrible down really low but as soon as the power tubes get pushed some it’s a different beast.

I guess my post thinking now I’ve woken up is basically a built in attenuater ?

only amp I remember trying this on was an orange tv50 which sounded amazing at talking volume.
Think attenuater answers my question to be fair :rolleyes:
 

Matthews Guitars

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A few things to know are that part of power stage saturation and THAT sound is due to the output transformer reaching magnetic saturation, which clips the waveform in a unique way of its own. Usually that's described as "grind" because it sounds like a grinding noise. And, most amps use a push-pull ouput stage using pairs of tubes, one of which handles the positive half of the waveform, and the other handles the negative half. This creates a natural "common mode rejection" phase cancellation, which results in the suppression of even order harmonics, leaving only odd order harmonics.

Thus, the harmonics of these stages when overdriven are characteristic of both the circuit and what components are being overdriven.

Single ended output stages (one output tube) have the same distortion characteristic as a preamp tube being overdriven.

Push-pull output stages have a different sound and different harmonics.

And if the transformer is in saturation, that adds its own harmonic tonality.

Trying to duplicate these sounds requires you to first determine which of them you want to duplicate.
 

mrjones2004x

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A few things to know are that part of power stage saturation and THAT sound is due to the output transformer reaching magnetic saturation, which clips the waveform in a unique way of its own. Usually that's described as "grind" because it sounds like a grinding noise. And, most amps use a push-pull ouput stage using pairs of tubes, one of which handles the positive half of the waveform, and the other handles the negative half. This creates a natural "common mode rejection" phase cancellation, which results in the suppression of even order harmonics, leaving only odd order harmonics.

Thus, the harmonics of these stages when overdriven are characteristic of both the circuit and what components are being overdriven.

Single ended output stages (one output tube) have the same distortion characteristic as a preamp tube being overdriven.

Push-pull output stages have a different sound and different harmonics.

And if the transformer is in saturation, that adds its own harmonic tonality.

Trying to duplicate these sounds requires you to first determine which of them you want to duplicate.
I never knew a transformer working hard was part of the sound honestly. I always thought just the tubes and transformer just for power requirements.
 

Pete Farrington

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the output transformer reaching magnetic saturation
My experience is that actual OT saturation is very unusual, much more mentioned than ever occurring in valve guitar amps. Ive only ever observed it in a vintage Gibson amp that had a ridiculously miniscule OT. It got hot when overdriven, and the amp sounded pretty ratty.
A saturated magnetic circuit will lose its ability to support the inductance of the coil, ie the primary impedance of the OT collapes to equal its resistance.
Anode / cathode current in the output valves will shoot up significantly for the parts of the waveform where the OT saturates.
Are you sure the behaviour you’re referring to is OT saturation?
A vintage type OT’s BH curve will start rounding off well before saturation; that’s one of the differences between old school (eg M6) and modern (eg M28) silicon steels, which have a sharper ’knee’.

I think that milder non linearity is the effect most people mean regarding this. Saturation per se is different, much more extreme, and pretty stressful on everything.

Even then, saturation is only really a low frequency thing; as frequency increases, so does a magnetic circuit’s saturation threshold.

If your scope can display 10-20Hz signals, try running your amp at the onset of clipping into a resistive load at say 200Hz, and then at 10 to 20Hz. The differences (big bites out of the waveform) are probably due to the OT magnetic circuit saturating.
Leave it running like that for a while and the OT will probably tend to heat up, but bear in mind that also means the valve anodes will be getting pushed.
Also try monitoring the waveform across a 1ohm cathode resistor.

I acknowledge that it’s just a terminology thing and I’m probably being nitpicky, but that’s my bag :) :rolleyes:
 
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Matthews Guitars

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One of my amps is a Fender Tremolux, which is a Pro Reverb circuit with a very undersized output transformer. If you run 6L6 power tubes in it, it will definitely saturate the OT. Not surprisingly, this amp sounds best when pushed, but not when cranked all the way. It gets ugly at 10, but is pretty magical at 7.
 

Pete Farrington

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But ugly overdrive in black panel Fenders is typically due to bias shift leading to blocking distortion.
Even that little OT might only actually saturate on a full power low E, if at all.
Whereas all frequencies will cause and be affected by bias shift (though reducing the bias excursion time will help to make it less apparent).
What’s the reason you’re ascribing it to OT saturation?
 
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william vogel

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The output transformer doesn’t saturate in anything we’re doing except possibly what Pete is talking about. The only chance of saturating the transformer would be by sending it a much lower frequency. Guitar and bass instruments are what our amplifiers are designed to play and if you do some testing, you’ll prove to yourself that saturation isn’t occurring.
When it occurs voltage will stop rising, current will rise quickly and heat will build quickly.
 

william vogel

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If one wanted to experience output transformer saturation, the use of an inferior very low wattage rated transformer such as a Hammond 1760F with a quad of el34’s while loading the 16 ohm secondary tap with 4 ohms. I don’t think the sound would be entertaining. The lower frequencies would simply reach a maximum volume and higher frequencies would continue to play louder. If the duty wasn’t conservative, failure would result.
 


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