• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube subwoofer amp

Hi all,

Well after getting my 6V6 PP stereo amp sounding real nice, (check my other threads) I am looking for a new project.

I have a 10"sub in a box sitting around, and access to a variety of big *** tubes (some smaller transmitting triodes and stuff) which I can get for free. I am wondering about using a single-ended triode amp with negative feedback, using one of these tubes. My question is: what kind of power/output transformers would I need?

I was thinking I would need a reasonable power tranny, however the amp would probably only have 2 tubes: an octal triode like the 6SN7 as a preamp (heck, maybe even a 6V6 as a preamp!) and a big coke bottle power tube. So maybe I could get away with a scrounged tranny from a big console radio... Maybe?

I am thinking around 30W RMS would be good enough for a fair bit of bass, could I use a toroidal power transformer as an opt? I only need a freq range of 20-120 Hz, and I am using NFB, so would that be good enough?

Any other crazy person thought about this (or done it :D)



2002-06-06 4:43 am
Tube sub amp

Why do you want to use a tube amp for the sub. A large tube amp capable of 20 Hz at full output must be very large and expensive.
On the other hand you could use a Hybrid amp with tube front end and transistor ( bipolar or Mosfet) output stage. This way you can go into the x100 watt range. They will also have better damping ( lower output impedance ) at the critical bass frequencies and have better low frequency response.
I like your ambition. This sub in a box.........speaker cabinet shaped like a box.........cardboard box, what are we looking at here?
As far as a reasonable amp for the sub the easiest and cheapest thing to do would to be getting your hands on an old piece of integrated SS gear and strapping it into mono.
For what your talking about which is a volume adjustable amp it would take a lot of work. For amps of that ilk what I have seen is a dual triode driving a power tube driving a transmitting tube. That much work deserves much more that subwoofer duty.

But I still want you to do it so we can find out about it! OK?


2002-01-07 6:02 pm
Unless you have some real horn subs, and can get the output iron would and optimised for low frequency performance, get a nice big SS unit. You'll be happier and have a fuller wallet.

Sure, if you want to build a big-mutha tube amp for your sub, look no further than the <a href="http://bulk.pearl-hifi.com/Misc_Downloads/Altec_260A_Instr.pdf">Altec 260A</a> , a 260W/ch beast. Only requires 2 x 6AU6 and 2 x 813 per channel (+rectifiers), and good Russian 813s are about $US12 each. A pair of 813's lit up at full power produces the most amazing light show, heat and creates almost a forcefield in the air around them. Very impressive for the neighbours and friends.

I have no idea where to get the parts like iron and PSU caps, but I would caution you to keep one hand behind your back at all times when building and working on it. It has a B+ of 1800V and the 813s have anode caps. I'd rather our DIYers didn't become charcoal prematurely, and I'd <i>strongly</i> advise not using it around children or pets you care about.:p

Seriously folks, unless you really know what you're doing, amps voltages this high should not be attempted unless you are <b>very</b> well versed in all the safety requirements. Even thinking about it should absolve diyaudio, Pearl and me from any liability. Link provided for educational and entertainment purposes only.

(being mean now :) )
did you consider and 845 PP? (or maybe 211 PP?)
You would need 1200V of B+ however but you would get 100W if you drive the babies a little bit into class-B.

Gintaras (ebay: kwtubes) sells the Russian equivalent to the 845, having 20V of heater voltage instead of 10 but else pretty much the same as the 845. Maybe he also has an idea where to get decent PP trannies?
I am using a Dynaco ST 70 with modifications to the front end. I have a 3 foot by 3 foot by 2 foot enclosure with 2 12 inch subwoofers in it. It is a bass reflex tunned to 20 HZ. Each speaker is driven by one of the channels of the ST 70 and the input comes from my Denon reciever sub preamp output and goes to a wye adaptor to the inputs of the 2 channel ST70 amp. I have a Mark III dynaco on the front left and another on the front right and these are all custom built all horn speakers. I have another Dynaco ST70 for the in wall rear surround speakers. They are JBL units. I have a Mono Block that puts out about 50 watts for the center channel that I custom built. It drives a custom speaker that I made for the center front audio. The system is very nice and sounds better than the Denon SS outputs. The Bass will shake the room.
I run my speakers (inclus a 10" sub) from a commercial sold Prima Luna Prologue 4 amp (35w) and easely hit 25Hz with it (i did run the 10" ported before tuned to 25Hz). But that is a very advanced PP amp with EL34 output tubes amp with good OPT's that can handle that. It's not impossible, but you need a good OPT and a well thought over amp circuit i think.

And a British guy i know called Paul Axis runs a retro reggae soundsystem (Axis Valv-A-Tron) with a self build 1500w tube amp on the bass section (tuned to 35Hz). It has a lot of 807 tubes. It's a huge monster, but it sounds wonderfull. Not easy to build and maintain altough, but he is a tube amp specialist who also sells (smaller) tube amps and more for a living. The photo attached is that amp next to his wife (for size reference like he said).

You can find more info about this soundsystem here: Axis Valv-a-tron Sound System. - Home | Facebook


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