tiny valve amps

bottledtone · 2010-12-06T09:51:05+00:00

Hi there guys. I'm a amp builder from nelspruit. I build custom amps, and been wondering if you think There is a market for small valve amps in the 1 watt range. I actually like playing a quarter watt I built. It uses the pentode section of a 6an8a valve. Having two young kids has made me look in the lower power amp range.

dt

Hi Bottledtone,
Please include me on the PM, am also looking but more in the smaller range as you mentioned. Some of the commercial ones allow one to toggle between 1w and 5w for example - do you do anything like this ?

bottledtone

dt wrote Hi Bottledtone,
Please include me on the PM, am also looking but more in the smaller range as you mentioned. Some of the commercial ones allow one to toggle between 1w and 5w for example - do you do anything like this ?

Wished I found this forum ages ago. ?
dt: Anything is possible in the realm of valveamps (almost everything) ? for eg. A 30 watt amp with 4 x EL84's..... a switch to run all in triode mode as 15watts, a switch to disconnect 2 x EL84, now 7 watts or switch back to pentode and now 15 watts agian, and then run as a self-split (mesa call this SE in their express 5:25 or 5:50 but it is actually a self-split output), to get you 5 watts, and then you guessed it, back as triode, and now you have 2 watts. (all plus/minus figures of course ?)

5 watts could be had from a SE design using EL84's, 6V6's or a PP using say.......2 x 12au7's which are 4 x triodes, that you could switch out.

Then....... a voltage control over the whole amp gives you control over wattage like a Master bigg daddy volume.

will get to prices.

69Thinline

Hey guys, new to the forum! Yah a small amp sounds AWESOME, unfortunately it does come down to cost-so an indication would be great to let u know how seriously intent I would be on it!
Bottledtone-you don't perhaps know roland and patti barnard do u? They told me they knew an amp builder in nelspruit??

bottledtone

69Thinline: Yeah, they planted the church I'm part of.
I believe the one guy I built an amp for is friends of the family.

Bad time of year to get exact prices.
Still settling on a circuit.

69Thinline

Yoh! Small world! My sister is married 2 their son, seth and my dad is friends with allen and daleen!
Keep me posted on the amps!

VellaJ

bottledtone: The idea of a small 1W or 5W tube amp is great. I experimented with building a 1W solid-state amp recently, and it works really well.

One question - how portable would it be? The solid state one I built runs off a 12V alarm battery, so you wouldn't need to always be plugged in to use it. Would this be possible for your valve amp as well?

bottledtone

VellaJ: With the power cuts that we get so much of I have looked into the battery option. Problem is that the little hot glass suckers suck lots of current to get their pretty glow and the voltage required to get power is normally pretty high. This results in a quick flat battery.
I have tryed to get space charge valves for experiments, but have not been able to get my hands on them. They run on 6v to 36v depending on which one. But that still only gives in milliwatts.
The Dc to Dc converter is also an option, but i really do like a chassis complete with a mains and output transformer.
Headphone valve amp with battery......yes.

I have ordered my transformers for my 1-2 watt amp. Gain,tone, volume. Push pull with a post PI volume. Really like the idea of calling it naartjie, since the orange tiny terror is the inspiration. The lil night train was only spotted by me later. Still considering if it should be handwired or on a printed board. I do want weight to be low and it to be small. Head and cab.

VellaJ

Yeah I had a feeling the valves would draw a lot of current. I guess if you want valves you have be be able to make do with only having the mains.

I like the idea of printed circuit boards, but they can be a bit of a monster to fix if they go wrong (depending on the complexity obviously). So I generally go for hand wired. But to keep size down, I think your board would be the best ?

bottledtone

Finally got my transformer for a little prototype. They work out to only R100 cheaper than 15 watt transformers. The idea has gone towards a blend of tiny terror and night train, to become "night terror".
Will have gain bass treble cut and volume. The boost will lift the bass treble and then the cut will be the master tone.

Kalcium

If the price is good enough I may be interested as well! ? I think everyone needs a low watt valve amp for home use, or at least, everyone should have one ?

69Thinline

I got my eye on this thread...

ratrap

Me too.

bottledtone

Prototype chassis is coming along, just working on the eyelet board at the moment. Been juggling between having a cathodyne PI or a LTP.

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Just a rough chassis for now.

Gearhead

??? Are those drilled holes? I just had everything lasered... Admittedly not all sockets were to spec so I did have to file and drill out a bit, but if you get all parts in before designing, laser is the way to go imho.

bottledtone

Like I said... A rough chassis for a prototype. I don't waste money on myself. My amps that are sold off are "water jet" cut and worked out completely before. Then bent and powder coated.
I'm building this one for myself and it is made from an already powdered coated aluminium rec tube.

Gearhead

bottledtone wrote Been juggling between having a cathodyne PI or a LTP.

The arguments for using a split load PI aren't that many. You do only use one triode, but for the lack of gain you do need a driver in front of it (especially if you want to add nfb). With this driver, you might wind up with too much gain. If you then start driving the splitter triode into clip, it has a tendency to fart out. Only when using output tubes with a low input current requirement, you can get away with the poor output power as well. Long tail pair it is imho.

bottledtone

That "farting out" sound can be fixed by just adding a nice big grid stopper of 470k to 1M to stop it from drawing to much current when it overdrives and that fixes that problem. The other thing is that the ouput is low and a 12au7 as and output valve doesn't need lots of drive, so thats why i haven't jumped at the LTP.
Was thinking of a bootstrapped master volume on the phase inverter too, but I've settled on a dual ganged PPIV.

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