EBC41 double-diode triode booster

[ppaappoo]

Hi, i build a booster with a EBC41 double-diode triode, only use the triode section. But i have a problem, when use a 100nF input cap the pedal don't work but when i jumper-ed it works fine.

I make this scheme, run with a 6+6v trafo, the plate voltage is 20VDC



Datasheet: http://www.r-type.org/pdfs/ebc41.pdf

[Derringer]

I believe you need a resistor from the grid to ground

try another 1 M

[jasperoosthoek]

Without the resistor suggested by Derringer the grid can float freely. What happens is that it charges to a value where the tube is outside its operating point.

But you don't need the input cap at all because the grid will be at 0V DC. Instead you could replace it with a resistor (68k is uses a lot) to limit the grid current when a large positive voltage is applied. Current will flow when the grid is more positive than the cathode. A resistor helps to limit that. Keep the 1M resistor in place. You will still need that one.

[ppaappoo]

OK, so on the eagle scheme change the C1 with a 68k resistor and R3 leave in 1M.  What resistor first?

[jasperoosthoek]

It does not matter at all to which side of the 68k resistor the 1M is connected. Both sides are ok. For the cap it does matter as it can float.

The problem with your schematic arose when you changed the order of the input cap and Rg. You learned a lot which is great. The input cap was there in the first place because the original circuit blocked DC. A guitar amp/booster generally does not need to do that so you can remove the input cap. But if you keep the cap in place you would you have to modify your nice finished PCB. I suggest to keep the PCB as it is.

So, if you remove the cap you might as well add something functional instead of a jumper wire.  The 68k resistor that I've seen in so many circuits is not absolutely critical. I searched a bit why they are there and it appears also to be a high frequency cutoff. It will not alter the sound at all and might improve your amps stability. http://www.regiscoyne.com/tech/68kinput/

Reading that links tells me I have to include it in a subminiature tube buffer amp that I've built last your and put to serious use a few weeks ago. It picks up radio signals and (I think) doesn't have the 68k cap... So another reason to include it in your build! 

[tubelectron]

Hi - simply remove C1, because your tube isn't biased (no grid reference to GND), or put it before the resistor (and you may lower it to 10n if you still choose 1M grid resistor value) - A+!

[ppaappoo]

Thank you all, replace the cap input through a resistance of 68k and seems to work well. Very quiet and zero hum thanks to the internal protective grid serves as a Faraday cage.
The final volume is not excessive considering that the EBC41 has an amplification factor of 70 but definitely boost the signal.

I recommend to you and this radio tubes are not expensive.

If some one wants the pcb, just let me know and i'll upload it.

[ppaappoo]

[markeebee]

Nice work Ppaappoo.

I've got a couple of EBC41, never thought about using them as a booster because it seemed a shame to NOT use the diode sections. But that's just silly.

Please could you upload or PM me your pcb, I'd like to make this.

Thanks!

[jasperoosthoek]

Great work man! But keep in mind that the amplification factor will not be 70 (thats 37dB!). As your anode voltage is only 20 volts it will be much lower.

[Renegadrian]

Great!!! 

[ppaappoo]

Great work man! But keep in mind that the amplification factor will not be 70 (thats 37dB!). As your anode voltage is only 20 volts it will be much lower.

Yes, I imagine that, it would be best to design a source of 110v or 150v and 6.3v for the filaments.
But the idea was to make a valve boost pedal super cheap and easy with recycled scrap. I'll do it later with a better power supply

Here is the PCB, you can use any 8-pin tube having a triode inside, just mod the PCB.

http://www.mediafire.com/?z2q9dw333y82klv

[jasperoosthoek]

Nothing wrong with a 20 volts anode voltage. My tube booster has an anode voltage of only 10 volts... If you increase the voltage of the tube you might consider a volume control if you don't have one already.

[ppaappoo]

Nothing wrong with a 20 volts anode voltage. My tube booster has an anode voltage of only 10 volts... If you increase the voltage of the tube you might consider a volume control if you don't have one already.

Do you know a way to make a 6v 110v power supply?

[tubelectron]

Hi ppaappoo,

Yes : assuming your 6V are AC, use a 6V / 120V (or 230V) 3VA transformer, full wave bridge rectifier, resistors and filter caps, and you should have something like 130-150VDC filtered. I use it regularly with success in my tube pedals . You can see the Xformer on the following innards views :






Here is a pic of the Xfo, it's Crovisa-made, 2x6V / 220V / 3VA :



And here is the convenient schematic for it. Perfectly reliable and hum-less - IF you place the transformer CORRECTLY and/or SHIELD it by a aluminium SCREEN, indeed.



There is also chips which can do the job, but I didn't experimented it. I'm sure other DIYers here have...

A+!

[jasperoosthoek]

frequencycentral posted a lot on step up chips on this and the ax84 forum.

[ppaappoo]

Thanks for the info.

[ppaappoo]

I would like a power supply that does not use transformers, which only becomes a 230vac to DC and then through a voltage divider to get 6.3 v and the plate voltage.

[tubelectron]

Hi again,

To my knowledge, there's no such "small compact all integrated" circuit which would be able to give you directly from the 230VAC say 250VDC 5mA and 6,3VDC 0,5A both filtered, but I may be wrong ! In addition, I am not sure it would complies with electric safety regulation, for insulation matters.

When I say directly, I mean no transformer indeed and no (or strict minimum) additional components... If you find such device, please let us know !

A+!

[ppaappoo]

Hi again,

To my knowledge, there's no such "small compact all integrated" circuit which would be able to give you directly from the 230VAC say 250VDC 5mA and 6,3VDC 0,5A both filtered, but I may be wrong ! In addition, I am not sure it would complies with electric safety regulation, for insulation matters.

When I say directly, I mean no transformer indeed and no (or strict minimum) additional components... If you find such device, please let us know !

A+!

I think the best would be a  transformer with 6v and 110v outlets.