Question on headroom and wattage

[giodata]

Hello everyone!
I have looked through some forums looking for answer to a question but it seems none have really answered it.

What exactly does headroom and wattage depend on in a tube amplifier? Assuming I have a 50 watt amplifier whose clean tones I love and saturated tones I love, but I wanted to increase the headroom while keeping the same tone coloration was something I was interested in. Would it be as “simple” as installing bigger PT’s and OT’s and higher wattage rated tubes? Or should I be looking at something else?

Any help would be appreciated, thanks.

[xtian]

Welcome to TAG.

Tube amps have a limit to how much clean output power they can deliver, based on PT voltage and current, power tubes used, OT capability, etc. "Headroom" is a difficult term to interpret for guitar amps. I know "headroom" from the digital recording world. Like, "How much more amplitude can I capture to disk before I start to digitally clip the signal?" I guess you are asking, "I like the sound of my amp, but wish it could get louder." True? If so, let's hear what amp it is, what tubes, what voltages and bias, what speakers are you using? If not true, please reframe your question.

[giodata]

Hey!
Your definition of headroom is pretty much spot on for what I was intending to say. In a sense “My clean signal starts to clip when the volume knob turns past 4, how do I make it so it doesn’t do that until the volume knob turns past 6” .
I’m aware that volume is logarithmic, and I guess from what I’ve read about it and with my current understanding at the moment is that it highly depends on the speakers.
The amp in question here is a 5E3 deluxe, modded to the specification of a dumble tweedle dee as seen on Rob robinette’s page (https://robrobinette.com/5e3_Modificati ... e_Dee_Mods). It uses a pair of 6v6’s and a pair of 12ax7s. I have incorporated a solid state rectifier. This amp uses 3 10 inch speakers by Jupiter Condenser, rated at 25watts, they have a sensitivity of 96.5 dB. The power transformer is a classic tone #40-18078 and the output transformer is a CT #40-18090. I don’t have the voltages or bias on hand as I built this amplifier at school, and now I am home, 250 miles away.

[xtian]

Changing to SS rectifier (and therefore getting higher B+), as you've done, is one way to increase power.

Regarding the volume knob, you are sending a clean signal to the PI and power tubes, and when this signal gets to a certain amplitude, the signal distorts (in this circuit, the PI distorts first, I believe). It doesn't matter if the volume knob reads is "4" at that point, or "6" or "11", the effect is the same--you have exceeded your headroom! So, you could put in a lower gain tube in V1 like 12AT7, but again, you're not going to increase the clean output power of the amp this way.

Your best bet is more efficient speakers. 96dB sensitivity is inefficient, compared to alternatives. Look at Eminence EM12: 101.1 dB! That's a significant difference.

Another alternative is a device like Bad Cat's Unleashed, which runs your amp's signal through a solid state power amp.

[giodata]

Thank you for your help and suggestions. A speaker swap is most likely what I see in the near future. And as a side note, other then an SS rectifier and more efficient speakers, what else could be done to increase clean output of an amp?

[martin manning]

And as a side note, other then an SS rectifier and more efficient speakers, what else could be done to increase clean output of an amp?

Consider switching to fixed bias on the output tubes. Such a mod is described on the site linked above, here: https://robrobinette.com/5e3_Modificati ... hable_Bias

[giodata]

Thanks for this, I will 100% be incorporating this into my build when I get back to it.

[norburybrook]

can you put 6L6's with your OT? I did that with my tweedle dee for more power, works very well in that amp. Also if you want to have a more blackface clean tone then experiment with the NFB by using different values on a switch also mentioned on Robs site. It's a simple mod but really useful, you can put it on a footswitch too. this amp has a LOT of bass so that can be an issue at times.



M

[giodata]

I originally hoped to remedy the Tweed Deluxe’s farting bass issue by implementing the mods + the 3 by 10 speakers , but the more and more I looked at the mods and read them, I realized that rob was absolutely right in saying it will no longer sound anything like a deluxe and in his words, it would be more “high strung”. I didn’t really care at that point, so I went ahead anyway with the mods. I have a hole drilled for the NFB and have a 56k ohm resistor for it as well. I thought about putting in 6L6’s but I don’t know if my output transformer could pair up with them. Where would be able to find out if my OT can handle a pair of 6L6’s? I have the specification sheet available as they all are on Classic tone’s website. Also how would the biasing work since the amp is originally for a pair of 6V6’s? Really appreciate the suggestions.


-gio

[xtian]

Please specify the OT for us.

[giodata]

The output transformer is a Classic Tone #40-18090

http://www.classictone.net/40-18090.html

Spec sheet: http://www.classictone.net/40-18090.pdf

[sluckey]

You can put 6L6s in the amp. No changes required. But... the yellow 4Ω tap becomes 2Ω, the green 8Ω tap becomes 4Ω, and the orange 16Ω tap becomes 8Ω. Don't expect any more power.

[giodata]

Would I be able to use the second speaker input jack that is available and wire in a way where I have an option between one jack being 8 ohms, for 6v6s and the other being 16 ohms for 6L6’s ?

[sluckey]

no

[roberto]

I have to say that often "headroom" is approached by increasing power, but I don't (always) agree.
Yes, on paper the higher the wattage, the highest the maximum volume, so the highest the difference between no signal and maximum signal, but... there's a but.

Headroom for guitar and bass players is often a feeling, and so the classic engineer's approach is not always the winning solution.
For example, you'll find alot of people feeling the Mesa Dynawatt as a very dynamic 20W power amp, while the Marshall 9200 with his 200W per side is not as much, and that is apparently a nonsense.
IMHO is the right compression and the right transition into saturation that give headroom to an (instrument) amp.

I've found this to be realistic with many normal players (guitars & bass mainly).