Tremolux 5G9 w/ NFB loop

[KenyonMI]

I am thinking of getting a tremolux 5G9 made for me and I just had a question, would the 5G9 benefit from a negative feedback loop? How is the clean headroom on the stock 5G9 which has no NFB loop? I don't really like the tweed deluxe which has no NFB loop but I like the other tweed amps like the 5F2a princeton that do have the NFB loop just because they will stay cleaner a little higher up the dial. I really like the tweed bassman which also has a NFB loop, I like how the bassman can go up to about 4.5 on the dial and remain relatively clean. Would the tremolux need a NFB loop in order to remain clean on up the dial like that bassman or is the tremolux pretty clean already even without a NFB loop? Is there any issues with the circuit in adding a NFB loop? Thanks

[The Dude]

Just thinking out loud: Since it's a build, why not make NFB switchable? It shouldn't cost much- a couple resistors and a switch. Or, add a pot and make it variable. This way, you could play with options and see what you like best.

[Enzo]

Or at the very least, put it in, knowing that if you prefer, all you have to do is disconnect the wire to it.

[pdf64]

I … I don't really like the tweed deluxe …

Lots of people fit 12AX7 in V1 of 5E3 tweed deluxe, which increases gain and perhaps muddiness / compression. How about those that you’ve tried, 12AX7 or 12AY7 in V1?
Plus the 5E3 output valves are cathode biased, idling at high anode current, so the stage gain will be high, whereas the 5G9 is fixed bias, so can be idled cooler, and so have a lower stage gain.

[loudthud]

An NFB loop will try to kill the Tremolo. Can anyone find a bias wiggle tremolo with NFB ?

[Chuck H]

An NFB loop will try to kill the Tremolo. Can anyone find a bias wiggle tremolo with NFB ?

6G16 Vibroverb

But I tried it with a build and I'm not convinced it's a good idea. The trem is "okay" but could be better. I'm probably going to change it.

[pdf64]

An NFB loop will try to kill the Tremolo. Can anyone find a bias wiggle tremolo with NFB ?

I think the regular black panel Princeton and Princeton Reverb has that combination, but the NFB ratio looks pretty small https://el34world.com/charts/Schemat..._schematic.pdf
If the bias is too hot, the trem effect depth is reported to be poor.

[guitman321]

I have 6g11 and 6g16 and the tremolo is fine. I do run cold bias, around 50%.

[KenyonMI]

I never thought about the NFB loop affecting the tremolo but that does make sense. If I did do it I would definitely make a switch to go on and off. I have been trying to read up on it and seems people say the 5G9 tremolux stays pretty clean almost half way up the dial and so it may not even need a NFB loop. What sparked my curiosity about a NFB loop in a 5G9 was in reference to a 5F11 which has a similar trem, similar wattage, and it does have a NFB loop. If anyone has any experience, does the stock 5G9 have at least as much clean headroom as a 5F11?

[Chuck H]

I have 6g11 and 6g16 and the tremolo is fine. I do run cold bias, around 50%.

I had poorer results running cold than hot in my build. But I may be asking too much of the effect. I DO want it vibrant and able to go full cut off, but I also want it smooth. I think one problem in my case is that the amp runs about 475Vp on modern El34's. I may just bias colder and reduce the oscillator swing influence. But this isn't a project that's a priority right now. Thanks for the report about NFB amps using bias wiggle.

[Helmholtz]

In the context of guitar amps clean headroom typically means available clean output (numbers on pot dials don't have a meaning by themselves).
NFB doesn't increase output power and will not noticably increase clean headroom.
Also NFB only affects the power section, most notably showing in less power stage gain. Means that you need more preamp signal/gain for the same output.
This in turns may cause increased preamp distortion depending on the circuit.

NFB does change the sound and "feel" of an amp, though.

[pdf64]

… What sparked my curiosity about a NFB loop in a 5G9 was in reference to a 5F11 which has a similar trem, similar wattage, and it does have a NFB loop. If anyone has any experience, does the stock 5G9 have at least as much clean headroom as a 5F11?

Bear in mind that the 5G9 was nearly 3 years after the 5F11. And Fender’s objective for the development of their amp models seems to be for the amps to be perceived as louder, cleaner. So it seems likely that if the Fender designers thought the 5G9 would benefit from a NFB loop, they’d have added it.

[KenyonMI]

Yea I agree, my intuition is telling me yes the 5G9 is cleaner than the 5F11 regardless of the NFB loop. I was just curious so thought I would ask. Thanks, if anyone has any more info all is welcome of coarse.

[Enzo]

Keep in mind, especially in that era - the amps are not consistent. All 5G9 amps didn't sound alike. They used low tolerance parts and tubes were luck of the draw.. It is really difficult to compare models based upon ONE factor and expect consistent meaningful results.

[Helmholtz]

Even 2 identical amps may appear to have different "headroom" as one of them starts distorting with volume at 3 and the other with volume at 5.

Simple explanation: Vol pots having different tapers.

Bottom line: Headroom only makes sense when related to a power measurement.