Other Amps

Adding Bias V tremolo to a 5F6A - Will it change the tone


Thinking of adding an extra valve for a simple bias vary trem to my home build 5f6a. Will it effect the tone when not engaged?

I remember Billy talking about his concert trem staying in the circuit off or on. (know it is dif trem circuit)

I'm aware that there are some great pedals (And know how much ppl here love the strymon) but not keen to add another one to the chain as i dont have/want a board and P/S.

At the moment i just have the Nocturne Atomic Brain (converted to take a 9v) and Boss DM3. Sometimes a 6G15 for verb. (I know the DM and Verb will change the tone but can be unplugged)

Keen to hear experiences or opinions on the 5f6a +trem idea


It will not effect the tone when it's off, unlike the Concert tremolo. It sounds like a good idea to me (you can pretty much copy the circuit from a Princeton Reverb), though you'll note that few 6L6 amps have the bias trem. My experience in tinkering with my Twin reverb is that it's very hard to avoid "ticking" and "heartbeat" sounds when varying the bias on these big tubes.

Luckily the oscillator circuit is identical for most tremolo designs, so you can build that and try a few different ways of applying it to the signal. A well tuned opto-trem is still very nice. I think they just get a bad rep because the incandescent lightbulbs in many old amps are worn out.


Thanks Otter. I have a 6g9b tremolux and was going to just copy the circuit on that. only other 6L6 with BV trem I've had was a dual channel Vadis. Trem on one channel and wiggled the preamp rather than output tubes.


A company called Area 51 used to make a little unit you could wire into your amp to add bias vary tremolo. I bought a couple and they work very well. They use a single 12ax7 and you screw it into the cab just below the chassis. I used a speaker out hole to run the wiring into the amp and it's all quite straightforward to install.

So, emboldened by this I then switched the tremolo in some AB763 style amps to bias vary, copied from the Vibroverb (I think) schematic.

So as long as you have somewhere to put the extra tube you should be fine adding tremolo to a 5F6-A circuit. The only issues may be making sure the extra tube doesn't tax the power tranny - shouldn't really be an issue with a 5F6-A. And sometimes you have to watch how much plate voltage you get on the tremolo tube, as too high will make it not oscillate. And make sure you do use the dual triode tremolo as the single triode version won't oscillate 6L6s.

As long as the P/T is happy pushing an extra tube the tremolo won't affect your tone at all and you will have IMO the best tremolo available.


Thanks Jimmy. That's exactly what I wanted to hear. I remember seeing those are51 kits as I was thinking of using it for my Supro. The Supro was a lil different though as it has a physicaly separate preamp and power amp.


The 6G11-A bias vary tremelo circuit is a good one. It works in 6L6 amps or 6V6s. I have it in a blackface vibrolux build and in a couple deluxes


The pedal looks great, Strummerson!


Thank you Toxophilite! It's all systems go now. will start the research.

The amp is perfect for a big hollow with a drummer in a practice room. I do think it may be way to loud for the kinda venues I play though.

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