small valve amp into power amp??

[15000volts]

I was wondering if having a small valve amp(15-20W, maybe? as low as it gets w/ good tone) connected to a separate power amp would work for smallish gigs. Having a small head spares the trouble of having to spend all my savings on one, and then breaking my back carrying it. It would also allow me to crank it up to break point, so I could have that nice warmth and fattiness off tubes, and then adjust the power amp to my needs. since the power amp stays after the valve amp, it maintains the od/break up point, but enables me to have it louder if I need.
Now, in my head, it seems reasonable, but is it really? also, how much do you reckon I'd have to spend on the power amp? the bass dedicated power amps I've seen are hardly what one could consider affordable(read: i'd have to sell one of my kidneys to afford one) well, the SWR Amplite is less than 600€, but for that price I'd rather buy a 300W SS head and stick with that.

[runmikeyrun]

you can't run a power amp into another power amp. You'll melt both amps. You could put an attenuator on the first amp and then if you're SURE it's a line level signal run that into the power amp's input, but then there's the argument about attenuators (power brake, etc) changing tone. A cranked power amp gives great distortion, but some of that tone comes from the speakers being pushed and moving a lot of air.

[15000volts]

I guess that's the end of it, then, thanks.

[BassmanPaul]

It's perfectly possible to do what you ask. Run the tube amp into a dummy load. Across the dummy load put a pot with a resistor in series. hot > resistor > top of pot. Bottom of pot > cold/ground. Slider of pot > power amp in. 10KΩ audio/log pot, 47KΩ resistor.

[pfschim]

I am no electrical/amp genius, but if the small tube(valve) amp had a line level out, or an FX send/out, you could run that signal into the power amp without any real risk.

So an example might be a Fender Bassman 100, which I think has a line out. You could use the Bassman 100 into a 1x15 (for example) for smallish gigs, then for larger gigs you could use its line out (it may be called "record out") into a much larger power amp (like a QSC PLX1802 - 1100w into 8ohms or 1800w into 4 ohms bridged mono) and drive a big set of cabs for brain crushing volume.

But the real question I would have is, why would you not just use a Tube pre into a nice power amp for all gigs (these are very light rigs), and just adjust the number of cabs and your power/volume level accordingly ? So, an Alembic F1X into a QSC PLX1802 briged mono into a nice TL606 1x15 cab .. with the power amp level adjusted down for small gigs, then for big gigs, the same pre/power amp set-up into a honking 8x10 or 4x12 (or whatever silly large cab arrangement you might like) and the power level cranked up to earth moving levels.

[quilttopjazz24]

Running a tube/valve amplifier without a speaker or other load connected to the speaker terminals is asking for trouble.

With respect, I would question Paul's advice too. Tube amps don't like open circuits and 47KΩ is darn close to open when the amp is expecting a 4, 8, or 16Ω load.

[christw]

There are a couple of attenuators I've seen with line outputs like a Weber MiniMass I used to run a Valve Junior into. It'll work, just be excessively careful about not running too much power into your big power amp.

[christw]

Originally Posted by quilttopjazz24

Running a tube/valve amplifier without a speaker or other load connected to the speaker terminals is asking for trouble.

With respect, I would question Paul's advice too. Tube amps don't like open circuits and 47KΩ is darn close to open when the amp is expecting a 4, 8, or 16Ω load.

Paul was saying to run it into a dummy load (like an attenuator) first.

[quilttopjazz24]

Originally Posted by christw

Paul was saying to run it into a dummy load (like an attenuator) first.

Thanks--I read Paul's post too quickly. My bad...

[BassmanPaul]

Originally Posted by quilttopjazz24

Thanks--I read Paul's post too quickly. My bad...

Some people say I know damn nothing! I tell them I know damn all!!!

Suitable dummy load resistors can be had from Parts Express. The resistor and the pot drop the available signal level 5:1. The pot acts as a master level.

[quilttopjazz24]

Originally Posted by BassmanPaul

Some people say I know damn nothing! I tell them I know damn all!!!

What a strange coincidence--I know damn's brother dick

[BassmanPaul]

Originally Posted by quilttopjazz24

What a strange coincidence--I know damn's brother dick

let's not forget Tom and Harry!

Funnily enough, in reality Tom WAS my dad and Harry his brother.

[MikeM]

That is pretty much how the Bass BATT works .. its a 5 watt amp that runs into a load so you can get power tube distortion at line level...I have one and it works great but it eats tubes, the bottom gets real mushy when the el84 needs changed.

[Munjibunga]

Originally Posted by BassmanPaul

It's perfectly possible to do what you ask. Run the tube amp into a dummy load. Across the dummy load put a pot with a resistor in series. hot > resistor > top of pot. Bottom of pot > cold/ground. Slider of pot > power amp in. 10KΩ audio/log pot, 47KΩ resistor.

That's simple enough.

[pharaohamps]

There are some amps that use this principle - the Guytron GT100 comes to mind. It's got a 15W EL84 power amp that is run through an output transformer and dummy load to a 100W EL34 power amp. The EL84 amp is just there for the tone, and the 100W power amp is pretty much clean.

The Garnet Herzog was basically a single-ended 6V6 amp similar to a Fender champ that was run into a dummy load and used as an overdrive effect, most famously on The Guess Who's "American Woman."

The Vox Valvetronix series uses a single preamp tube in a push-pull configuration into a simulated inductor to get some of the flavor of a bigger tube amp. The Vox design is very interesting in that it reconfigures the "Valve Reactor" tube section depending on what model is selected in the digital preamp section of the amp. The "output transformer" analog is a circuit called a gyrator, which acts like an inductor and has inductive resonance.

In my experience, a lot of the distortion character of an amp is created in the phase inverter section, which is why I prefer post phase inverter master volumes. I've built an amp with three different phase inverters that let me listen to the different characteristics of each, and the most popular phase inverters all have very different gain structures and sounds.

If you're using a dummy load on the output of your amplifier, please make sure that it is rated for the full wattage that you intend to apply to it. Most resistors will blow open if they exceed their rated power dissipation. A slightly safer method would be to use a commercial power attenuator. This may net a more pleasing tone, as most power attenuators provide some sort of inductance to simulate the back-current of a speaker.

Good luck!

[Munjibunga]

VT Bass into power amp. Now that's simple.

[NecroticImbecil]

"EXT AMP" jack, next to the "HUM CONTROL" on the right. I don't know how how affordable B-15s are where you live though.

[tombowlus]

Originally Posted by MikeM

That is pretty much how the Bass BATT works .. its a 5 watt amp that runs into a load so you can get power tube distortion at line level...I have one and it works great but it eats tubes, the bottom gets real mushy when the el84 needs changed.

The BATT does indeed work very well in this regard. But another option is to take a low power tube head (I like the Epiphone Valve, Jr., and it's cheap), or even a higher powered head, and send the output into the "Speaker In" on an Avalon U5 (or another DI box that accepts a speaker-level input - I think Countryman does?), and then send that signal on to the amplification rig of your choice. You may need to hook up a dummy load to your tube amp, though the Epiphone Valve, Jr. Hotrod has a built-in dummy load output (which was intended to allow it to be used as a reverb tank, but you don't need to use the reverb).

[BassmanPaul]

Originally Posted by NecroticImbecil

"EXT AMP" jack, next to the "HUM CONTROL" on the right.

All this does is allow the B15 pre-amp to drive another tube power amp. If you connect this to a modern SS power amp it'll load down the signal so much that the rest of the B15 pretty much stops working. There's also not enough signal level to push a SS power amp.

The who;e point of the exercise is to get the overdriven output tubes into the picture.

[pharaohamps]

Originally Posted by tombowlus

...or even a higher powered head, and send the output into the "Speaker In" on an Avalon U5 (or another DI box that accepts a speaker-level input - I think Countryman does?), and then send that signal on to the amplification rig of your choice.

It's no U5, but the Behringer DI100 and GI100 both accept speaker-level inputs. They do not have the ability to sink any kind of current, so you will need a dummy load or speaker as you mentioned.

If you're serious about the whole thing, a decent attenuator like the Weber MASS or Load Dump for around $100 would give you a range of choices. Why not run two different low-watt tube amps into a mixer and then into your big bass amp? The sky's the limit if you use your imagination (insert unicorns and rainbows here...)