Batteries to increase Anode voltage in LoV designs?

[bea]

Well, it is about low voltage (tube overdrive...) design. Traditionally run at 12V. Recent tubes, especially JJ ECC82, are fairly unusable at this anode voltage. To my experience they need at least 18V (to operate similarly well as NOS tubes).

My idea: stack one or even two 9V blocks on top of the 12V in order to raise the anode voltage into the working range. We'll still be somewhere in the microampere range - so a battery would las "forever". Is there anything to consier in such a design?
Especially: will it harm the tubes if there is that small 9 V voltage on the electrodes when the tubes are cold?

Thanks


Beate

[Enzo]

Batteries also have to run the tube heaters.

On the other hand, you could simply use higher voltage batteries. For example:

https://www.amazon.com/Exell-Battery.../dp/B00IDXP26S

[loudthud]

The battery idea is ok, but it's fairly trivial to make any Voltage you might need. One chip and an inductor the size of a 1W resistor, a cap or two and a couple of resistors. Another idea if you want to use 300V or so is the power supply from a disposable flash camera. Check the trash at your local photo processing store.

[Helmholtz]

There seems to be some confusion and a schematic of the device or a simple drawing of the intended wiring would help.

I understand that the unit is normally powered from an external 12VDC source.
The 12V are used for plate as well as heater supply.
As you only want to raise the plate supply voltage and not the heater voltage, the extra batteries will be wired in series with (on top of the) the heater supply.
Means they will be wired between the positive side of the heater and the plate supply, right?

[bea]

Yes, of course the batteryshall be wired in series with the heater supply for the anodes only. i.e, neg pole of batterie to +12V of the heater and pos. pole to the anode resistors. So we have 21V on the anode rail which is sufficent for ECC82 by JJ.

Background: this shall become a floor pedal where supplying more than one single voltage is not practicable.

There are of course alternatives like using a 12V AC supply for the heater and recitfying with a voltage doubler. or using a small internal transformer back to back to obtain high internal voltage (which is something i would like to avoid on such a simple device for my effects chain).

But i just want to be able to use some old 12V DC supply i already own.

[Helmholtz]

In short, I can't imagine a problem for the tubes with 9V between plates and heater. Any cold cathode turn-on current will be limited by the plate resistors.

[Dave H]

A little isolated DC-DC converter could be used, say 12V to 24V 1W. Connect its input to the 12V supply and stack its output on the 12V for a 36V plate supply.

[mozz]

I've built the valvecasters before and used ac on the filaments and rectified for the plate and got over 18v. With a 12AU7 it works fine.

[J M Fahey]

Not sure it will stay in the "microampere" range if raised .

Please post *actual* schematic.

In any case, have a look at B K Butler´s Real Tube design, including the US Patent.

He uses 2 triodes in different ways, one is the classic one, it does NOT pass current with meager 9V plate supply so in practice passes only the negative half wave, but the second triode is used with positive bias on grid, and can amplify signal in a linear way, even provide up to 3 Vpp clean.
Overdriving it will be equivalent to overdriving a normal triode, with normal (high) voltage supply.

You might experiment with building a conventional triode gain stage and applying positive bias with a trikmmer until you get reasonable results, then overdrive it as you wish.

[bea]

There seems to be some confusion and a schematic of the device or a simple drawing of the intended wiring would help.

I understand that the unit is normally powered from an external 12VDC source.
The 12V are used for plate as well as heater supply.
As you only want to raise the plate supply voltage and not the heater voltage, the extra batteries will be wired in series with (on top of the) the heater supply.
Means they will be wired between the positive side of the heater and the plate supply, right?

That is exactly what i had planned an meanwhile it works like a charm. Even a somewhat worn out 9V battery suffices - i am testing with 8.2V additional voltage. At 20.7V B+ the (EH) ECC82 apparently behaves pretty similar to the high voltage situation: a very nice warm clean tone, no chance to overdrive the 2nd stage ("sugar box" / "valvecaster" design - which is in strict contrast to the situation at 12.5V B+.

Not quite what i wanted, at least at present i need to drive it into distortion), but a nice result anyway.

[mozz]

Have you tried a old 12au7 to see what plate voltage works? They are fairly common so no need to buy a new 12au7 which probably doesn't come close to old quality. I think i had mine working well with a 12at7 also.

[bea]

No, I have not. I don't own old ECC82. And i actually do not see te need - just in order to be able to run te circuit at 12.5V. It looks as if i even can use older 9V batteries that had to be replaced in my basses to deliver the few microamperes the tubes can draw at these low voltages.

Anyway, one of my next steps will be trying out ECC83s in that settings (and here i even have a few old tubes to exepriment with) and see what happens.

A real world bass overdrive will probably more complex because it might be better to bypass the low frequencies without distortion. Which means a 2nd tube or one or two additional JFETs.

[mozz]

The reason i was saying to try a old tube, chances are the new production tubes may meet published specs, they are totally different manufacturer than older tubes and probably won't work when you are using them outside of what they were made for. 12AU7 are very common and low priced. A 12AX7 will not work in that circuit with low plate voltages. If you want to use new production you are gonna need more voltage so a different power supply will be needed.

[bea]

Here in Germany all the well known sources have increased their prices drastically. ANY old tube is a lot more expensive that the newer ones. The times of cheap, even affordable tubes are gone.

[bea]

Did a few tests with old, heavily used tubes - ECC83 and ECC81, both Telefunken, taken from old amps. The ECC83 somehow worked (!) but still was a bit silent. Obviously needs even larger B+ (It would be interesting to figure out the lowest B+ these tubes begin to work "reasonably"). The ECC81 worked nicely - good amplification and a nice overdrive could be achieved. It would be perfect if these tubes were not microphonic (which i hat previously they are - not usable in "V1" situations and loud surroundings).


So: the booster project is actually a success, but i learned that a real and adjustable tube booster and possible overdrive needs more effort.