Headroom Questions

[Jeff_H]

I'm not a big clean headroom guy, but there is something I don't understand. I don't need the NASA explaination, just the Readers Digest one.

I have it in my head that amps with 6L6's and similar tubes have the most "clean headroom", with EL34's in the middle, EL84's next down the line, then 6v6's. That may not be the exact order, but I generally think of 6L6's as having the most "headroom", and others as having "less".

Hiwatts are generally thought of as monster clean headroom amps (at least that's how I've heard them described), yet they are EL34 and 12AX7 based, like a Marshall...which I generally DO NOT think of as a clean headroom beast.

Is this "headroom" thing more a function of the ciruit design, the tube employed in the power stage, or something else I just don't understand. Again, just the "headroom for dummies" version is fine for me.

Thanks in advance.

 

[the guy who invented fire]

Re: Headroom Questions

It has less to do with the tube and more to do with the circut...that said the tube does come into play...

 

[Vasshu the humanoid typhoon]

Re: Headroom Questions

The transformers are huge on a Hiwatt!
Plus they are setup for a clean sound, so not much clipping going on.
They are coupled for clear clean sound.

 

[Jeff_H]

Re: Headroom Questions

Ok, so the majority of it has to do with circuit design and power trannies. So in theory, you could design an EL84 amp with more headroom than one with 6L6's or EL34's, or am I over simplifying it?

 

[PUCKBOY99]

Re: Headroom Questions

Ok, so the majority of it has to do with circuit design and power trannies. So in theory, you could design an EL84 amp with more headroom than one with 6L6's or EL34's, or am I over simplifying it?

Correct......the DST U-84 I had was 1 side Hiwatt & 1 side Marshall Super Lead running 2 EL84s & 4 preamp tubes.

Circuit + tubes + speakers = overall design

And don't even get started with the KT s

 

[Jeff_H]

Re: Headroom Questions

I left the KT's out on purpose Terry, because they confuse me so much. :lmao:

Due to my apparent ignorance on the subject, I have purposly stayed away from or outright disliked amps that are 6L6 or 6550 based because I have always felt they lacked the type of distortion and breakup I like so much, due to my perception of the type of headroom they have. Now that I have a little better understanding, and know that the ciruit has more to do with it than tubes, perhaps I'll not be such a biased pig.

Well, probably not.

Thanks for the info guys!

 

[kmcguitars]

Re: Headroom Questions

Ok, so the majority of it has to do with circuit design and power trannies. So in theory, you could design an EL84 amp with more headroom than one with 6L6's or EL34's, or am I over simplifying it?

In theory you could, But it would be impractical. The circuit would have to be very sterile to keep the EL84 from clipping. The physical size of the tube itself plays into the factor. Example, It would take much more voltage current to send a 6550 into clipping than a EL84.

 

[Quencho092]

Re: Headroom Questions

is this why fender twins are the stuff?

 

[some_dude]

Re: Headroom Questions

Hiwatts are generally thought of as monster clean headroom amps (at least that's how I've heard them described), yet they are EL34 and 12AX7 based, like a Marshall...which I generally DO NOT think of as a clean headroom beast.

See Rid's post....


....then swap the Hiwatt's EL34s for 6L6s.....or KT88s.

 

[frankfalbo]

Re: Headroom Questions

I would be more likely to say it's the circuit + other components than the tubes. A tube only has so much power it can take before it clips. It's up to the amp designer to decide how much they'll allow through. Take a non-master volume head, and put a governor in there that only allows the volume pot to go from 1-3. Now, that amp has all the clean headroom in the world within it's operating range, right?

Pre and post CBS Fenders are a good example. They have the same basic tube quantities and types, but the older ones broke up earlier. CBS downed the gains and cleaned up the circuits. The only time the tube type correlates directly with clean headroom is when you have a minimum volume requirement. So if you need a 50 watt half stack, EL84's probably won't give you enough "clean headroom" even if you're using four of them. But a 6L6 pair can either be designed to clip at 50 watts, or remain clean, whatever the amp maker is trying to achieve.